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<img alt="Erlang logo" src="../../../doc/erlang-logo.png"><br><small><a href="users_guide.html">User's Guide</a><br><a href="index.html">Reference Manual</a><br><a href="release_notes.html">Release Notes</a><br><a href="../pdf/erts-5.9.3.1.pdf">PDF</a><br><a href="../../../doc/index.html">Top</a></small><p><strong>Erlang Run-Time System Application (ERTS)</strong><br><strong>Reference Manual</strong><br><small>Version 5.9.3.1</small></p>
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<li id="no" title="erl_prim_loader " expanded="false">erl_prim_loader<ul>
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<li title="start-3"><a href="erl_prim_loader.html#start-3">start/3</a></li>
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<li title="get_path-0"><a href="erl_prim_loader.html#get_path-0">get_path/0</a></li>
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<li title="adler32_combine-3"><a href="erlang.html#adler32_combine-3">adler32_combine/3</a></li>
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<li title="binary_to_list-3"><a href="erlang.html#binary_to_list-3">binary_to_list/3</a></li>
<li title="bitstring_to_list-1"><a href="erlang.html#bitstring_to_list-1">bitstring_to_list/1</a></li>
<li title="binary_to_term-1"><a href="erlang.html#binary_to_term-1">binary_to_term/1</a></li>
<li title="binary_to_term-2"><a href="erlang.html#binary_to_term-2">binary_to_term/2</a></li>
<li title="bit_size-1"><a href="erlang.html#bit_size-1">bit_size/1</a></li>
<li title="bump_reductions-1"><a href="erlang.html#bump_reductions-1">bump_reductions/1</a></li>
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<li title="check_old_code-1"><a href="erlang.html#check_old_code-1">check_old_code/1</a></li>
<li title="check_process_code-2"><a href="erlang.html#check_process_code-2">check_process_code/2</a></li>
<li title="crc32-1"><a href="erlang.html#crc32-1">crc32/1</a></li>
<li title="crc32-2"><a href="erlang.html#crc32-2">crc32/2</a></li>
<li title="crc32_combine-3"><a href="erlang.html#crc32_combine-3">crc32_combine/3</a></li>
<li title="date-0"><a href="erlang.html#date-0">date/0</a></li>
<li title="decode_packet-3"><a href="erlang.html#decode_packet-3">decode_packet/3</a></li>
<li title="delete_module-1"><a href="erlang.html#delete_module-1">delete_module/1</a></li>
<li title="demonitor-1"><a href="erlang.html#demonitor-1">demonitor/1</a></li>
<li title="demonitor-2"><a href="erlang.html#demonitor-2">demonitor/2</a></li>
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<li title="erase-0"><a href="erlang.html#erase-0">erase/0</a></li>
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<li title="exit-1"><a href="erlang.html#exit-1">exit/1</a></li>
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<li title="external_size-1"><a href="erlang.html#external_size-1">external_size/1</a></li>
<li title="external_size-2"><a href="erlang.html#external_size-2">external_size/2</a></li>
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<li title="fun_info-1"><a href="erlang.html#fun_info-1">fun_info/1</a></li>
<li title="fun_info-2"><a href="erlang.html#fun_info-2">fun_info/2</a></li>
<li title="fun_to_list-1"><a href="erlang.html#fun_to_list-1">fun_to_list/1</a></li>
<li title="function_exported-3"><a href="erlang.html#function_exported-3">function_exported/3</a></li>
<li title="garbage_collect-0"><a href="erlang.html#garbage_collect-0">garbage_collect/0</a></li>
<li title="garbage_collect-1"><a href="erlang.html#garbage_collect-1">garbage_collect/1</a></li>
<li title="get-0"><a href="erlang.html#get-0">get/0</a></li>
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<li title="get_keys-1"><a href="erlang.html#get_keys-1">get_keys/1</a></li>
<li title="get_stacktrace-0"><a href="erlang.html#get_stacktrace-0">get_stacktrace/0</a></li>
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<li title="hibernate-3"><a href="erlang.html#hibernate-3">hibernate/3</a></li>
<li title="integer_to_list-1"><a href="erlang.html#integer_to_list-1">integer_to_list/1</a></li>
<li title="integer_to_list-2"><a href="erlang.html#integer_to_list-2">integer_to_list/2</a></li>
<li title="iolist_to_binary-1"><a href="erlang.html#iolist_to_binary-1">iolist_to_binary/1</a></li>
<li title="iolist_size-1"><a href="erlang.html#iolist_size-1">iolist_size/1</a></li>
<li title="is_alive-0"><a href="erlang.html#is_alive-0">is_alive/0</a></li>
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<li title="is_binary-1"><a href="erlang.html#is_binary-1">is_binary/1</a></li>
<li title="is_bitstring-1"><a href="erlang.html#is_bitstring-1">is_bitstring/1</a></li>
<li title="is_boolean-1"><a href="erlang.html#is_boolean-1">is_boolean/1</a></li>
<li title="is_builtin-3"><a href="erlang.html#is_builtin-3">is_builtin/3</a></li>
<li title="is_float-1"><a href="erlang.html#is_float-1">is_float/1</a></li>
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<li title="is_function-2"><a href="erlang.html#is_function-2">is_function/2</a></li>
<li title="is_integer-1"><a href="erlang.html#is_integer-1">is_integer/1</a></li>
<li title="is_list-1"><a href="erlang.html#is_list-1">is_list/1</a></li>
<li title="is_number-1"><a href="erlang.html#is_number-1">is_number/1</a></li>
<li title="is_pid-1"><a href="erlang.html#is_pid-1">is_pid/1</a></li>
<li title="is_port-1"><a href="erlang.html#is_port-1">is_port/1</a></li>
<li title="is_process_alive-1"><a href="erlang.html#is_process_alive-1">is_process_alive/1</a></li>
<li title="is_record-2"><a href="erlang.html#is_record-2">is_record/2</a></li>
<li title="is_record-3"><a href="erlang.html#is_record-3">is_record/3</a></li>
<li title="is_reference-1"><a href="erlang.html#is_reference-1">is_reference/1</a></li>
<li title="is_tuple-1"><a href="erlang.html#is_tuple-1">is_tuple/1</a></li>
<li title="length-1"><a href="erlang.html#length-1">length/1</a></li>
<li title="link-1"><a href="erlang.html#link-1">link/1</a></li>
<li title="list_to_atom-1"><a href="erlang.html#list_to_atom-1">list_to_atom/1</a></li>
<li title="list_to_binary-1"><a href="erlang.html#list_to_binary-1">list_to_binary/1</a></li>
<li title="list_to_bitstring-1"><a href="erlang.html#list_to_bitstring-1">list_to_bitstring/1</a></li>
<li title="list_to_existing_atom-1"><a href="erlang.html#list_to_existing_atom-1">list_to_existing_atom/1</a></li>
<li title="list_to_float-1"><a href="erlang.html#list_to_float-1">list_to_float/1</a></li>
<li title="list_to_integer-1"><a href="erlang.html#list_to_integer-1">list_to_integer/1</a></li>
<li title="list_to_integer-2"><a href="erlang.html#list_to_integer-2">list_to_integer/2</a></li>
<li title="list_to_pid-1"><a href="erlang.html#list_to_pid-1">list_to_pid/1</a></li>
<li title="list_to_tuple-1"><a href="erlang.html#list_to_tuple-1">list_to_tuple/1</a></li>
<li title="load_module-2"><a href="erlang.html#load_module-2">load_module/2</a></li>
<li title="load_nif-2"><a href="erlang.html#load_nif-2">load_nif/2</a></li>
<li title="loaded-0"><a href="erlang.html#loaded-0">loaded/0</a></li>
<li title="localtime-0"><a href="erlang.html#localtime-0">localtime/0</a></li>
<li title="localtime_to_universaltime-1"><a href="erlang.html#localtime_to_universaltime-1">localtime_to_universaltime/1</a></li>
<li title="localtime_to_universaltime-2"><a href="erlang.html#localtime_to_universaltime-2">localtime_to_universaltime/2</a></li>
<li title="make_ref-0"><a href="erlang.html#make_ref-0">make_ref/0</a></li>
<li title="make_tuple-2"><a href="erlang.html#make_tuple-2">make_tuple/2</a></li>
<li title="make_tuple-3"><a href="erlang.html#make_tuple-3">make_tuple/3</a></li>
<li title="max-2"><a href="erlang.html#max-2">max/2</a></li>
<li title="md5-1"><a href="erlang.html#md5-1">md5/1</a></li>
<li title="md5_final-1"><a href="erlang.html#md5_final-1">md5_final/1</a></li>
<li title="md5_init-0"><a href="erlang.html#md5_init-0">md5_init/0</a></li>
<li title="md5_update-2"><a href="erlang.html#md5_update-2">md5_update/2</a></li>
<li title="memory-0"><a href="erlang.html#memory-0">memory/0</a></li>
<li title="memory-1"><a href="erlang.html#memory-1">memory/1</a></li>
<li title="min-2"><a href="erlang.html#min-2">min/2</a></li>
<li title="module_loaded-1"><a href="erlang.html#module_loaded-1">module_loaded/1</a></li>
<li title="monitor-2"><a href="erlang.html#monitor-2">monitor/2</a></li>
<li title="monitor_node-2"><a href="erlang.html#monitor_node-2">monitor_node/2</a></li>
<li title="monitor_node-3"><a href="erlang.html#monitor_node-3">monitor_node/3</a></li>
<li title="nif_error-1"><a href="erlang.html#nif_error-1">nif_error/1</a></li>
<li title="nif_error-2"><a href="erlang.html#nif_error-2">nif_error/2</a></li>
<li title="node-0"><a href="erlang.html#node-0">node/0</a></li>
<li title="node-1"><a href="erlang.html#node-1">node/1</a></li>
<li title="nodes-0"><a href="erlang.html#nodes-0">nodes/0</a></li>
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<li title="now-0"><a href="erlang.html#now-0">now/0</a></li>
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<li title="phash2-1"><a href="erlang.html#phash2-1">phash2/1</a></li>
<li title="pid_to_list-1"><a href="erlang.html#pid_to_list-1">pid_to_list/1</a></li>
<li title="port_close-1"><a href="erlang.html#port_close-1">port_close/1</a></li>
<li title="port_command-2"><a href="erlang.html#port_command-2">port_command/2</a></li>
<li title="port_command-3"><a href="erlang.html#port_command-3">port_command/3</a></li>
<li title="port_connect-2"><a href="erlang.html#port_connect-2">port_connect/2</a></li>
<li title="port_control-3"><a href="erlang.html#port_control-3">port_control/3</a></li>
<li title="port_call-3"><a href="erlang.html#port_call-3">port_call/3</a></li>
<li title="port_info-1"><a href="erlang.html#port_info-1">port_info/1</a></li>
<li title="port_info-2"><a href="erlang.html#port_info-2">port_info/2</a></li>
<li title="port_to_list-1"><a href="erlang.html#port_to_list-1">port_to_list/1</a></li>
<li title="ports-0"><a href="erlang.html#ports-0">ports/0</a></li>
<li title="pre_loaded-0"><a href="erlang.html#pre_loaded-0">pre_loaded/0</a></li>
<li title="process_display-2"><a href="erlang.html#process_display-2">process_display/2</a></li>
<li title="process_flag-2"><a href="erlang.html#process_flag-2">process_flag/2</a></li>
<li title="process_flag-3"><a href="erlang.html#process_flag-3">process_flag/3</a></li>
<li title="process_info-1"><a href="erlang.html#process_info-1">process_info/1</a></li>
<li title="process_info-2"><a href="erlang.html#process_info-2">process_info/2</a></li>
<li title="processes-0"><a href="erlang.html#processes-0">processes/0</a></li>
<li title="purge_module-1"><a href="erlang.html#purge_module-1">purge_module/1</a></li>
<li title="put-2"><a href="erlang.html#put-2">put/2</a></li>
<li title="raise-3"><a href="erlang.html#raise-3">raise/3</a></li>
<li title="read_timer-1"><a href="erlang.html#read_timer-1">read_timer/1</a></li>
<li title="ref_to_list-1"><a href="erlang.html#ref_to_list-1">ref_to_list/1</a></li>
<li title="register-2"><a href="erlang.html#register-2">register/2</a></li>
<li title="registered-0"><a href="erlang.html#registered-0">registered/0</a></li>
<li title="resume_process-1"><a href="erlang.html#resume_process-1">resume_process/1</a></li>
<li title="round-1"><a href="erlang.html#round-1">round/1</a></li>
<li title="self-0"><a href="erlang.html#self-0">self/0</a></li>
<li title="send-2"><a href="erlang.html#send-2">send/2</a></li>
<li title="send-3"><a href="erlang.html#send-3">send/3</a></li>
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<li title="setelement-3"><a href="erlang.html#setelement-3">setelement/3</a></li>
<li title="size-1"><a href="erlang.html#size-1">size/1</a></li>
<li title="spawn-1"><a href="erlang.html#spawn-1">spawn/1</a></li>
<li title="spawn-2"><a href="erlang.html#spawn-2">spawn/2</a></li>
<li title="spawn-3"><a href="erlang.html#spawn-3">spawn/3</a></li>
<li title="spawn-4"><a href="erlang.html#spawn-4">spawn/4</a></li>
<li title="spawn_link-1"><a href="erlang.html#spawn_link-1">spawn_link/1</a></li>
<li title="spawn_link-2"><a href="erlang.html#spawn_link-2">spawn_link/2</a></li>
<li title="spawn_link-3"><a href="erlang.html#spawn_link-3">spawn_link/3</a></li>
<li title="spawn_link-4"><a href="erlang.html#spawn_link-4">spawn_link/4</a></li>
<li title="spawn_monitor-1"><a href="erlang.html#spawn_monitor-1">spawn_monitor/1</a></li>
<li title="spawn_monitor-3"><a href="erlang.html#spawn_monitor-3">spawn_monitor/3</a></li>
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<li title="suspend_process-2"><a href="erlang.html#suspend_process-2">suspend_process/2</a></li>
<li title="suspend_process-1"><a href="erlang.html#suspend_process-1">suspend_process/1</a></li>
<li title="system_flag-2"><a href="erlang.html#system_flag-2">system_flag/2</a></li>
<li title="system_info-1"><a href="erlang.html#system_info-1">system_info/1</a></li>
<li title="system_monitor-0"><a href="erlang.html#system_monitor-0">system_monitor/0</a></li>
<li title="system_monitor-1"><a href="erlang.html#system_monitor-1">system_monitor/1</a></li>
<li title="system_monitor-2"><a href="erlang.html#system_monitor-2">system_monitor/2</a></li>
<li title="system_profile-0"><a href="erlang.html#system_profile-0">system_profile/0</a></li>
<li title="system_profile-2"><a href="erlang.html#system_profile-2">system_profile/2</a></li>
<li title="term_to_binary-1"><a href="erlang.html#term_to_binary-1">term_to_binary/1</a></li>
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<div id="content">
<div class="innertube">
<!-- refpage --><center><h1>erlang</h1></center>
<h3>MODULE</h3>
<div class="REFBODY">erlang</div>
<h3>MODULE SUMMARY</h3>
<div class="REFBODY">The Erlang BIFs</div>
<h3>DESCRIPTION</h3>
<div class="REFBODY"><p>
<p>By convention, most built-in functions (BIFs) are seen as being
in the module <span class="code">erlang</span>. A number of the BIFs are viewed more
or less as part of the Erlang programming language and are
<strong>auto-imported</strong>. Thus, it is not necessary to specify
the module name and both the calls <span class="code">atom_to_list(Erlang)</span> and
<span class="code">erlang:atom_to_list(Erlang)</span> are identical.</p>
<p>In the text, auto-imported BIFs are listed without module prefix.
BIFs listed with module prefix are not auto-imported.</p>
<p>BIFs may fail for a variety of reasons. All BIFs fail with
reason <span class="code">badarg</span> if they are called with arguments of an
incorrect type. The other reasons that may make BIFs fail are
described in connection with the description of each individual
BIF.</p>
<p>Some BIFs may be used in guard tests, these are marked with
"Allowed in guard tests".</p>
</p></div>
<h3>DATA TYPES</h3>
<p><span class="bold_code"><a name="type-ext_binary">ext_binary()</a></span></p>
<div class="REFBODY"><p>
<p>A binary data object, structured according to
the Erlang external term format.</p>
</p></div>
<p>
<span class="bold_code"><a name="type-timestamp">timestamp()</a> = <br> {MegaSecs :: integer() >= 0,<br> Secs :: integer() >= 0,<br> MicroSecs :: integer() >= 0}</span><br></p>
<div class="REFBODY"><p><p>See <span class="bold_code"><a href="#now-0">now/0</a></span>.</p>
</p></div>
<h3>EXPORTS</h3>
<p><a name="abs-1"><span class="bold_code">abs(Number) -> integer() | float()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Number = number()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer or float which is the arithmetical
absolute value of <span class="code">Number</span>.</p>
<div class="example"><pre>
> <span class="bold_code">abs(-3.33).</span>
3.33
> <span class="bold_code">abs(-3).</span>
3</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="adler32-1"><span class="bold_code">erlang:adler32(Data) -> integer()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Computes and returns the adler32 checksum for <span class="code">Data</span>.</p>
</p></div>
<p><a name="adler32-2"><span class="bold_code">erlang:adler32(OldAdler, Data) -> integer()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">OldAdler = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Continue computing the adler32 checksum by combining
the previous checksum, <span class="code">OldAdler</span>, with the checksum of
<span class="code">Data</span>.</p>
<p>The following code:</p>
<div class="example"><pre>
X = erlang:adler32(Data1),
Y = erlang:adler32(X,Data2).
</pre></div>
<p>- would assign the same value to <span class="code">Y</span> as this would:</p>
<div class="example"><pre>
Y = erlang:adler32([Data1,Data2]).
</pre></div>
</p></div>
<p><a name="adler32_combine-3"><span class="bold_code">erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) -> integer()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">FirstAdler = SecondAdler = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">SecondSize = integer()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Combines two previously computed adler32 checksums.
This computation requires the size of the data object for
the second checksum to be known.</p>
<p>The following code:</p>
<div class="example"><pre>
Y = erlang:adler32(Data1),
Z = erlang:adler32(Y,Data2).
</pre></div>
<p>- would assign the same value to <span class="code">Z</span> as this would:</p>
<div class="example"><pre>
X = erlang:adler32(Data1),
Y = erlang:adler32(Data2),
Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).
</pre></div>
</p></div>
<p><a name="append_element-2"><span class="bold_code">erlang:append_element(Tuple1, Term) -> Tuple2</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Tuple1 = Tuple2 = tuple()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a new tuple which has one element more than
<span class="code">Tuple1</span>, and contains the elements in <span class="code">Tuple1</span>
followed by <span class="code">Term</span> as the last element. Semantically
equivalent to
<span class="code">list_to_tuple(tuple_to_list(Tuple) ++ [Term])</span>, but much
faster.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:append_element({one, two}, three).</span>
{one,two,three}</pre></div>
</p></div>
<p><a name="apply-2"></a><span class="bold_code">apply(Fun, Args) -> term()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Call a fun, passing the elements in <span class="code">Args</span> as
arguments.</p>
<p>Note: If the number of elements in the arguments are known at
compile-time, the call is better written as
<span class="code">Fun(Arg1, Arg2, ... ArgN)</span>.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>Earlier, <span class="code">Fun</span> could also be given as
<span class="code">{Module, Function}</span>, equivalent to
<span class="code">apply(Module, Function, Args)</span>. This usage is
deprecated and will stop working in a future release of
Erlang/OTP.</p>
</p></div>
</div>
</p></div>
<p><a name="apply-3"></a><span class="bold_code">apply(Module, Function, Args) -> term()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Module = module()</span></div>
<div class="REFTYPES"><span class="bold_code">Function = atom()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the result of applying <span class="code">Function</span> in
<span class="code">Module</span> to <span class="code">Args</span>. The applied function must
be exported from <span class="code">Module</span>. The arity of the function is
the length of <span class="code">Args</span>.</p>
<div class="example"><pre>
> <span class="bold_code">apply(lists, reverse, [[a, b, c]]).</span>
[c,b,a]</pre></div>
<p><span class="code">apply</span> can be used to evaluate BIFs by using
the module name <span class="code">erlang</span>.</p>
<div class="example"><pre>
> <span class="bold_code">apply(erlang, atom_to_list, ['Erlang']).</span>
"Erlang"</pre></div>
<p>Note: If the number of arguments are known at compile-time,
the call is better written as
<span class="code">Module:Function(Arg1, Arg2, ..., ArgN)</span>.</p>
<p>Failure: <span class="code">error_handler:undefined_function/3</span> is called
if the applied function is not exported. The error handler
can be redefined (see
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>).
If the <span class="code">error_handler</span> is undefined, or if the user has
redefined the default <span class="code">error_handler</span> so the replacement
module is undefined, an error with the reason <span class="code">undef</span>
is generated.</p>
</p></div>
<p><a name="atom_to_binary-2"><span class="bold_code">atom_to_binary(Atom, Encoding) -> binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Atom = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Encoding = latin1 | utf8 | unicode</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a binary which corresponds to the text
representation of <span class="code">Atom</span>. If <span class="code">Encoding</span>
is <span class="code">latin1</span>, there will be one byte for each character
in the text representation. If <span class="code">Encoding</span> is <span class="code">utf8</span> or
<span class="code">unicode</span>, the characters will be encoded using UTF-8
(meaning that characters from 16#80 up to 0xFF will be
encoded in two bytes).</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p>Currently, <span class="code">atom_to_binary(Atom, latin1)</span> can
never fail because the text representation of an atom can only contain
characters from 0 to 16#FF. In a future release, the text representation
of atoms might be allowed to contain any Unicode character
and <span class="code">atom_to_binary(Atom, latin1)</span> will fail if the
text representation for the <span class="code">Atom</span> contains a Unicode
character greater than 16#FF.</p></p></div>
</div>
<div class="example"><pre>
> <span class="bold_code">atom_to_binary('Erlang', latin1).</span>
<<"Erlang">></pre></div>
</p></div>
<p><a name="atom_to_list-1"><span class="bold_code">atom_to_list(Atom) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Atom = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Atom</span>.</p>
<div class="example"><pre>
> <span class="bold_code">atom_to_list('Erlang').</span>
"Erlang"</pre></div>
</p></div>
<p><a name="binary_part-2"><span class="bold_code">binary_part(Subject, PosLen) -> binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Subject = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">PosLen = {Start,Length}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Start = integer() >= 0</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Length = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Extracts the part of the binary described by <span class="code">PosLen</span>.</p>
<p>Negative length can be used to extract bytes at the end of a binary:</p>
<div class="example"><pre>
1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
2> binary_part(Bin,{byte_size(Bin), -5)).
<<6,7,8,9,10>>
</pre></div>
<p>If <span class="code">PosLen</span> in any way references outside the binary, a <span class="code">badarg</span> exception is raised.</p>
<p><span class="code">Start</span> is zero-based, i.e.:</p>
<div class="example"><pre>
1> Bin = <<1,2,3>>
2> binary_part(Bin,{0,2}).
<<1,2>>
</pre></div>
<p>See the STDLIB module <span class="code">binary</span> for details about the <span class="code">PosLen</span> semantics.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="binary_part-3"><span class="bold_code">binary_part(Subject, Start, Length) -> binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Subject = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Start = integer() >= 0</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Length = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The same as <span class="code">binary_part(Subject, {Pos, Len})</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="binary_to_atom-2"><span class="bold_code">binary_to_atom(Binary, Encoding) -> atom()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Binary = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Encoding = latin1 | utf8 | unicode</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the atom whose text representation is
<span class="code">Binary</span>. If <span class="code">Encoding</span> is <span class="code">latin1</span>, no
translation of bytes in the binary is done. If <span class="code">Encoding</span>
is <span class="code">utf8</span> or <span class="code">unicode</span>, the binary must contain
valid UTF-8 sequences; furthermore, only Unicode characters up
to 0xFF are allowed.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p><span class="code">binary_to_atom(Binary, utf8)</span> will fail if
the binary contains Unicode characters greater than 16#FF.
In a future release, such Unicode characters might be allowed
and <span class="code">binary_to_atom(Binary, utf8)</span>
will not fail in that case.</p></p></div>
</div>
<div class="example"><pre>
> <span class="bold_code">binary_to_atom(<<"Erlang">>, latin1).</span>
'Erlang'
> <span class="bold_code">binary_to_atom(<<1024/utf8>>, utf8).</span>
** exception error: bad argument
in function binary_to_atom/2
called as binary_to_atom(<<208,128>>,utf8)</pre></div>
</p></div>
<p><a name="binary_to_existing_atom-2"><span class="bold_code">binary_to_existing_atom(Binary, Encoding) -> atom()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Binary = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Encoding = latin1 | utf8 | unicode</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Works like <span class="bold_code"><a href="#binary_to_atom-2">binary_to_atom/2</a></span>,
but the atom must already exist.</p>
<p>Failure: <span class="code">badarg</span> if the atom does not already exist.</p>
</p></div>
<p><a name="binary_to_list-1"><span class="bold_code">binary_to_list(Binary) -> [char()]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Binary = binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of integers which correspond to the bytes of
<span class="code">Binary</span>.</p>
</p></div>
<p><a name="binary_to_list-3"><span class="bold_code">binary_to_list(Binary, Start, Stop) -> [char()]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Binary = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Start = Stop = 1..byte_size(Binary)</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>As <span class="code">binary_to_list/1</span>, but returns a list of integers
corresponding to the bytes from position <span class="code">Start</span> to
position <span class="code">Stop</span> in <span class="code">Binary</span>. Positions in the
binary are numbered starting from 1.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p>This function's indexing style of using one-based indices for
binaries is deprecated. New code should use the functions in
the STDLIB module <span class="code">binary</span> instead. They consequently
use the same (zero-based) style of indexing.</p></p></div>
</div>
</p></div>
<p><a name="bitstring_to_list-1"><span class="bold_code">bitstring_to_list(Bitstring) -> [char()|bitstring()]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Bitstring = bitstring()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of integers which correspond to the bytes of
<span class="code">Bitstring</span>. If the number of bits in the binary is not
divisible by 8, the last element of the list will be a bitstring
containing the remaining bits (1 up to 7 bits).</p>
</p></div>
<p><a name="binary_to_term-1"><span class="bold_code">binary_to_term(Binary) -> term()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Binary = <span class="bold_code"><a href="#type-ext_binary">ext_binary()</a></span></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an Erlang term which is the result of decoding
the binary object <span class="code">Binary</span>, which must be encoded
according to the Erlang external term format.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>When decoding binaries from untrusted sources, consider using
<span class="code">binary_to_term/2</span> to prevent denial of service attacks.</p>
</p></div>
</div>
<p>See also
<span class="bold_code"><a href="#term_to_binary-1">term_to_binary/1</a></span>
and
<span class="bold_code"><a href="#binary_to_term-2">binary_to_term/2</a></span>.</p>
</p></div>
<p><a name="binary_to_term-2"><span class="bold_code">binary_to_term(Binary, Opts) -> term()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Opts = [safe]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Binary = <span class="bold_code"><a href="#type-ext_binary">ext_binary()</a></span></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>As <span class="code">binary_to_term/1</span>, but takes options that affect decoding
of the binary.</p>
<dl>
<dt><strong><span class="code">safe</span></strong></dt>
<dd>
<p>Use this option when receiving binaries from an untrusted
source.</p>
<p>When enabled, it prevents decoding data that may be used to
attack the Erlang system. In the event of receiving unsafe
data, decoding fails with a badarg error.</p>
<p>Currently, this prevents creation of new atoms directly,
creation of new atoms indirectly (as they are embedded in
certain structures like pids, refs, funs, etc.), and creation of
new external function references. None of those resources are
currently garbage collected, so unchecked creation of them can
exhaust available memory.</p>
</dd>
</dl>
<p>Failure: <span class="code">badarg</span> if <span class="code">safe</span> is specified and unsafe data
is decoded.</p>
<p>See also
<span class="bold_code"><a href="#term_to_binary-1">term_to_binary/1</a></span>,
<span class="bold_code"><a href="#binary_to_term-1">binary_to_term/1</a></span>,
and <span class="bold_code"><a href="#list_to_existing_atom-1">
list_to_existing_atom/1</a></span>.</p>
</p></div>
<p><a name="bit_size-1"><span class="bold_code">bit_size(Bitstring) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Bitstring = bitstring()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer which is the size in bits of <span class="code">Bitstring</span>.</p>
<div class="example"><pre>
> <span class="bold_code">bit_size(<<433:16,3:3>>).</span>
19
> <span class="bold_code">bit_size(<<1,2,3>>).</span>
24</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="bump_reductions-1"><span class="bold_code">erlang:bump_reductions(Reductions) -> void()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reductions = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>This implementation-dependent function increments
the reduction counter for the calling process. In the Beam
emulator, the reduction counter is normally incremented by
one for each function and BIF call, and a context switch is
forced when the counter reaches the maximum number of reductions
for a process (2000 reductions in R12B).</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF might be removed in a future version of the Beam
machine without prior warning. It is unlikely to be
implemented in other Erlang implementations.</p>
</p></div>
</div>
</p></div>
<p><a name="byte_size-1"><span class="bold_code">byte_size(Bitstring) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Bitstring = bitstring()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer which is the number of bytes needed to contain
<span class="code">Bitstring</span>. (That is, if the number of bits in <span class="code">Bitstring</span> is not
divisible by 8, the resulting number of bytes will be rounded <strong>up</strong>.)</p>
<div class="example"><pre>
> <span class="bold_code">byte_size(<<433:16,3:3>>).</span>
3
> <span class="bold_code">byte_size(<<1,2,3>>).</span>
3</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="cancel_timer-1"><span class="bold_code">erlang:cancel_timer(TimerRef) -> Time | false</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">TimerRef = reference()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Time = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Cancels a timer, where <span class="code">TimerRef</span> was returned by
either
<span class="bold_code"><a href="#send_after-3">erlang:send_after/3</a></span>
or
<span class="bold_code"><a href="#start_timer-3">erlang:start_timer/3</a></span>.
If the timer is there to be removed, the function returns
the time in milliseconds left until the timer would have expired,
otherwise <span class="code">false</span> (which means that <span class="code">TimerRef</span> was
never a timer, that it has already been cancelled, or that it
has already delivered its message).</p>
<p>See also
<span class="bold_code"><a href="#send_after-3">erlang:send_after/3</a></span>,
<span class="bold_code"><a href="#start_timer-3">erlang:start_timer/3</a></span>,
and
<span class="bold_code"><a href="#read_timer-1">erlang:read_timer/1</a></span>.</p>
<p>Note: Cancelling a timer does not guarantee that the message
has not already been delivered to the message queue.</p>
</p></div>
<p><a name="check_old_code-1"><span class="bold_code">check_old_code(Module) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if the <span class="code">Module</span> has old code,
and <span class="code">false</span> otherwise.</p>
<p>See also <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>.</p>
</p></div>
<p><a name="check_process_code-2"><span class="bold_code">check_process_code(Pid, Module) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if the process <span class="code">Pid</span> is executing
old code for <span class="code">Module</span>. That is, if the current call of
the process executes old code for this module, or if the
process has references to old code for this module, or if the
process contains funs that references old code for this
module. Otherwise, it returns <span class="code">false</span>.</p>
<div class="example"><pre>
> <span class="bold_code">check_process_code(Pid, lists).</span>
false</pre></div>
<p>See also <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>.</p>
</p></div>
<p><a name="crc32-1"><span class="bold_code">erlang:crc32(Data) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Computes and returns the crc32 (IEEE 802.3 style) checksum for <span class="code">Data</span>.</p>
</p></div>
<p><a name="crc32-2"><span class="bold_code">erlang:crc32(OldCrc, Data) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">OldCrc = integer() >= 0</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Continue computing the crc32 checksum by combining
the previous checksum, <span class="code">OldCrc</span>, with the checksum of
<span class="code">Data</span>.</p>
<p>The following code:</p>
<div class="example"><pre>
X = erlang:crc32(Data1),
Y = erlang:crc32(X,Data2).
</pre></div>
<p>- would assign the same value to <span class="code">Y</span> as this would:</p>
<div class="example"><pre>
Y = erlang:crc32([Data1,Data2]).
</pre></div>
</p></div>
<p><a name="crc32_combine-3"><span class="bold_code">erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">FirstCrc = SecondCrc = integer() >= 0</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">SecondSize = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Combines two previously computed crc32 checksums.
This computation requires the size of the data object for
the second checksum to be known.</p>
<p>The following code:</p>
<div class="example"><pre>
Y = erlang:crc32(Data1),
Z = erlang:crc32(Y,Data2).
</pre></div>
<p>- would assign the same value to <span class="code">Z</span> as this would:</p>
<div class="example"><pre>
X = erlang:crc32(Data1),
Y = erlang:crc32(Data2),
Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
</pre></div>
</p></div>
<p><a name="date-0"><span class="bold_code">date() -> Date</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Date = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-date');">calendar:date()</a></span></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the current date as <span class="code">{Year, Month, Day}</span>.</p>
<p>The time zone and daylight saving time correction depend on
the underlying OS.</p>
<div class="example"><pre>
> <span class="bold_code">date().</span>
{1995,2,19}</pre></div>
</p></div>
<p><a name="decode_packet-3"><span class="bold_code">erlang:decode_packet(Type,Bin,Options) -> {ok,Packet,Rest} | {more,Length} | {error,Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Bin = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Options = [Opt]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Packet = binary() | HttpPacket</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Rest = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Length = integer() > 0 | undefined</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Type, Opt -- see below</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"></span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpPacket = HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpResponse = {http_response, HttpVersion, integer(), HttpString}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpHeader = {http_header, integer(), HttpField, Reserved=term(), Value=HttpString}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpError = {http_error, HttpString}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpMethod = HttpMethodAtom | HttpString</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpMethodAtom = 'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' | 'TRACE'</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpUri = '*' | {absoluteURI, http|https, Host=HttpString, Port=integer()|undefined, Path=HttpString} |
{scheme, Scheme=HttpString, HttpString} | {abs_path, HttpString} | HttpString</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpVersion = {Major=integer(), Minor=integer()}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpString = string() | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpField = HttpFieldAtom | HttpString</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">HttpFieldAtom = 'Cache-Control' | 'Connection' | 'Date' | 'Pragma' | 'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' | 'Accept-Charset' | 'Accept-Encoding' | 'Accept-Language' | 'Authorization' | 'From' | 'Host' | 'If-Modified-Since' | 'If-Match' | 'If-None-Match' | 'If-Range' | 'If-Unmodified-Since' | 'Max-Forwards' | 'Proxy-Authorization' | 'Range' | 'Referer' | 'User-Agent' | 'Age' | 'Location' | 'Proxy-Authenticate' | 'Public' | 'Retry-After' | 'Server' | 'Vary' | 'Warning' | 'Www-Authenticate' | 'Allow' | 'Content-Base' | 'Content-Encoding' | 'Content-Language' | 'Content-Length' | 'Content-Location' | 'Content-Md5' | 'Content-Range' | 'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' | 'Accept-Ranges' | 'Set-Cookie' | 'Set-Cookie2' | 'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' | 'Proxy-Connection'</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Decodes the binary <span class="code">Bin</span> according to the packet
protocol specified by <span class="code">Type</span>. Very similar to the packet
handling done by sockets with the option {packet,Type}.</p>
<p>If an entire packet is contained in <span class="code">Bin</span> it is
returned together with the remainder of the binary as
<span class="code">{ok,Packet,Rest}</span>.</p>
<p>If <span class="code">Bin</span> does not contain the entire packet,
<span class="code">{more,Length}</span> is returned. <span class="code">Length</span> is either the
expected <strong>total size</strong> of the packet or <span class="code">undefined</span>
if the expected packet size is not known. <span class="code">decode_packet</span>
can then be called again with more data added.</p>
<p>If the packet does not conform to the protocol format
<span class="code">{error,Reason}</span> is returned.</p>
<p>The following values of <span class="code">Type</span> are valid:</p>
<dl>
<dt><strong><span class="code">raw | 0</span></strong></dt>
<dd>
<p>No packet handling is done. Entire binary is
returned unless it is empty.</p>
</dd>
<dt><strong><span class="code">1 | 2 | 4</span></strong></dt>
<dd>
<p>Packets consist of a header specifying the number of
bytes in the packet, followed by that number of bytes.
The length of header can be one, two, or four bytes;
the order of the bytes is big-endian. The header
will be stripped off when the packet is returned.</p>
</dd>
<dt><strong><span class="code">line</span></strong></dt>
<dd>
<p>A packet is a line terminated with newline. The
newline character is included in the returned packet
unless the line was truncated according to the option
<span class="code">line_length</span>.</p>
</dd>
<dt><strong><span class="code">asn1 | cdr | sunrm | fcgi | tpkt</span></strong></dt>
<dd>
<p>The header is <strong>not</strong> stripped off.</p>
<p>The meanings of the packet types are as follows:</p>
<dl>
<dt><strong><span class="code">asn1</span> - ASN.1 BER</strong></dt>
<dd></dd>
<dt><strong><span class="code">sunrm</span> - Sun's RPC encoding</strong></dt>
<dd></dd>
<dt><strong><span class="code">cdr</span> - CORBA (GIOP 1.1)</strong></dt>
<dd></dd>
<dt><strong><span class="code">fcgi</span> - Fast CGI</strong></dt>
<dd></dd>
<dt><strong><span class="code">tpkt</span> - TPKT format [RFC1006]</strong></dt>
<dd></dd>
</dl>
</dd>
<dt><strong><span class="code">http | httph | http_bin | httph_bin</span></strong></dt>
<dd>
<p>The Hypertext Transfer Protocol. The packets
are returned with the format according to
<span class="code">HttpPacket</span> described above. A packet is either a
request, a response, a header or an end of header
mark. Invalid lines are returned as <span class="code">HttpError</span>.</p>
<p>Recognized request methods and header fields are returned as atoms.
Others are returned as strings.</p>
<p>The protocol type <span class="code">http</span> should only be used for
the first line when a <span class="code">HttpRequest</span> or a
<span class="code">HttpResponse</span> is expected. The following calls
should use <span class="code">httph</span> to get <span class="code">HttpHeader</span>'s until
<span class="code">http_eoh</span> is returned that marks the end of the
headers and the beginning of any following message body.</p>
<p>The variants <span class="code">http_bin</span> and <span class="code">httph_bin</span> will return
strings (<span class="code">HttpString</span>) as binaries instead of lists.</p>
</dd>
</dl>
<p>The following options are available:</p>
<dl>
<dt><strong><span class="code">{packet_size, integer()}</span></strong></dt>
<dd>
<p>Sets the max allowed size of the packet body. If
the packet header indicates that the length of the
packet is longer than the max allowed length, the packet
is considered invalid. Default is 0 which means no
size limit.</p>
</dd>
<dt><strong><span class="code">{line_length, integer()}</span></strong></dt>
<dd>
<p>For packet type <span class="code">line</span>, truncate lines longer
than the indicated length.</p>
<p>Option <span class="code">line_length</span> also applies to <span class="code">http*</span>
packet types as an alias for option <span class="code">packet_size</span> in the
case when <span class="code">packet_size</span> itself is not set. This usage is
only intended for backward compatibility.</p>
</dd>
</dl>
<div class="example"><pre>
> <span class="bold_code">erlang:decode_packet(1,<<3,"abcd">>,[]).</span>
{ok,<<"abc">>,<<"d">>}
> <span class="bold_code">erlang:decode_packet(1,<<5,"abcd">>,[]).</span>
{more,6}</pre></div>
</p></div>
<p><a name="delete_module-1"><span class="bold_code">delete_module(Module) -> true | undefined</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Makes the current code for <span class="code">Module</span> become old code, and
deletes all references for this module from the export table.
Returns <span class="code">undefined</span> if the module does not exist,
otherwise <span class="code">true</span>.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for the code server (see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>) and should not be
used elsewhere.</p>
</p></div>
</div>
<p>Failure: <span class="code">badarg</span> if there is already an old version of
<span class="code">Module</span>.</p>
</p></div>
<p><a name="demonitor-1"><span class="bold_code">demonitor(MonitorRef) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">MonitorRef = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>If <span class="code">MonitorRef</span> is a reference which the calling process
obtained by calling
<span class="bold_code"><a href="#monitor-2">monitor/2</a></span>,
this monitoring is turned off. If the monitoring is already
turned off, nothing happens.</p>
<p>Once <span class="code">demonitor(MonitorRef)</span> has returned it is
guaranteed that no <span class="code">{'DOWN', MonitorRef, _, _, _}</span> message
due to the monitor will be placed in the caller's message queue
in the future. A <span class="code">{'DOWN', MonitorRef, _, _, _}</span> message
might have been placed in the caller's message queue prior to
the call, though. Therefore, in most cases, it is advisable
to remove such a <span class="code">'DOWN'</span> message from the message queue
after monitoring has been stopped.
<span class="bold_code"><a href="#demonitor-2">demonitor(MonitorRef, [flush])</a></span> can be used instead of
<span class="code">demonitor(MonitorRef)</span> if this cleanup is wanted.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Prior to OTP release R11B (erts version 5.5) <span class="code">demonitor/1</span>
behaved completely asynchronous, i.e., the monitor was active
until the "demonitor signal" reached the monitored entity. This
had one undesirable effect, though. You could never know when
you were guaranteed <strong>not</strong> to receive a <span class="code">DOWN</span> message
due to the monitor.</p>
<p>Current behavior can be viewed as two combined operations:
asynchronously send a "demonitor signal" to the monitored entity
and ignore any future results of the monitor. </p>
</p></div>
</div>
<p>Failure: It is an error if <span class="code">MonitorRef</span> refers to a
monitoring started by another process. Not all such cases are
cheap to check; if checking is cheap, the call fails with
<span class="code">badarg</span> (for example if <span class="code">MonitorRef</span> is a remote
reference).</p>
</p></div>
<p><a name="demonitor-2"><span class="bold_code">demonitor(MonitorRef, OptionList) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">MonitorRef = reference()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">OptionList = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Option = flush | info</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The returned value is <span class="code">true</span> unless <span class="code">info</span> is part
of <span class="code">OptionList</span>.
</p>
<p><span class="code">demonitor(MonitorRef, [])</span> is equivalent to
<span class="bold_code"><a href="#demonitor-1">demonitor(MonitorRef)</a></span>.</p>
<p>Currently the following <span class="code">Option</span>s are valid:</p>
<dl>
<dt><strong><span class="code">flush</span></strong></dt>
<dd>
<p>Remove (one) <span class="code">{_, MonitorRef, _, _, _}</span> message,
if there is one, from the caller's message queue after
monitoring has been stopped.</p>
<p>Calling <span class="code">demonitor(MonitorRef, [flush])</span>
is equivalent to the following, but more efficient:</p>
<div class="example"><pre>
demonitor(MonitorRef),
receive
{_, MonitorRef, _, _, _} ->
true
after 0 ->
true
end</pre></div>
</dd>
<dt><strong><span class="code">info</span></strong></dt>
<dd>
<p>The returned value is one of the following:</p>
<dl>
<dt><strong><span class="code">true</span></strong></dt>
<dd>
<p>The monitor was found and removed. In this case
no <span class="code">'DOWN'</span> message due to this monitor have
been nor will be placed in the message queue
of the caller.
</p>
</dd>
<dt><strong><span class="code">false</span></strong></dt>
<dd>
<p>The monitor was not found and could not be removed.
This probably because someone already has placed a
<span class="code">'DOWN'</span> message corresponding to this monitor
in the caller's message queue.
</p>
</dd>
</dl>
<p>If the <span class="code">info</span> option is combined with the <span class="code">flush</span>
option, <span class="code">false</span> will be returned if a flush was needed;
otherwise, <span class="code">true</span>.
</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>More options may be added in the future.</p>
</p></div>
</div>
<p>Failure: <span class="code">badarg</span> if <span class="code">OptionList</span> is not a list, or
if <span class="code">Option</span> is not a valid option, or the same failure as for
<span class="bold_code"><a href="#demonitor-1">demonitor/1</a></span></p>
</p></div>
<p><a name="disconnect_node-1"></a><span class="bold_code">disconnect_node(Node) -> boolean() | ignored</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Forces the disconnection of a node. This will appear to
the node <span class="code">Node</span> as if the local node has crashed. This
BIF is mainly used in the Erlang network authentication
protocols. Returns <span class="code">true</span> if disconnection succeeds,
otherwise <span class="code">false</span>. If the local node is not alive,
the function returns <span class="code">ignored</span>.</p>
</p></div>
<p><a name="display-1"><span class="bold_code">erlang:display(Term) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Prints a text representation of <span class="code">Term</span> on the standard
output.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging only.</p>
</p></div>
</div>
</p></div>
<p><a name="element-2"><span class="bold_code">element(N, Tuple) -> term()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">N = 1..tuple_size(Tuple)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Tuple = tuple()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the <span class="code">N</span>th element (numbering from 1) of
<span class="code">Tuple</span>.</p>
<div class="example"><pre>
> <span class="bold_code">element(2, {a, b, c}).</span>
b</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="erase-0"><span class="bold_code">erase() -> [{Key, Val}]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Key = Val = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the process dictionary and deletes it.</p>
<div class="example"><pre>
> <span class="bold_code">put(key1, {1, 2, 3}),</span>
<span class="bold_code">put(key2, [a, b, c]),</span>
<span class="bold_code">erase().</span>
[{key1,{1,2,3}},{key2,[a,b,c]}]</pre></div>
</p></div>
<p><a name="erase-1"><span class="bold_code">erase(Key) -> Val | undefined</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Key = Val = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the value <span class="code">Val</span> associated with <span class="code">Key</span> and
deletes it from the process dictionary. Returns
<span class="code">undefined</span> if no value is associated with <span class="code">Key</span>.</p>
<div class="example"><pre>
> <span class="bold_code">put(key1, {merry, lambs, are, playing}),</span>
<span class="bold_code">X = erase(key1),</span>
<span class="bold_code">{X, erase(key1)}.</span>
{{merry,lambs,are,playing},undefined}</pre></div>
</p></div>
<p><a name="error-1"><span class="bold_code">error(Reason)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Stops the execution of the calling process with the reason
<span class="code">Reason</span>, where <span class="code">Reason</span> is any term. The actual
exit reason will be <span class="code">{Reason, Where}</span>, where <span class="code">Where</span>
is a list of the functions most recently called (the current
function first). Since evaluating this function causes
the process to terminate, it has no return value.</p>
<div class="example"><pre>
> <span class="bold_code">catch error(foobar).</span>
{'EXIT',{foobar,[{erl_eval,do_apply,5},
{erl_eval,expr,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}</pre></div>
</p></div>
<p><a name="error-2"><span class="bold_code">error(Reason, Args)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Args = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Stops the execution of the calling process with the reason
<span class="code">Reason</span>, where <span class="code">Reason</span> is any term. The actual
exit reason will be <span class="code">{Reason, Where}</span>, where <span class="code">Where</span>
is a list of the functions most recently called (the current
function first). <span class="code">Args</span> is expected to be the list of
arguments for the current function; in Beam it will be used
to provide the actual arguments for the current function in
the <span class="code">Where</span> term. Since evaluating this function causes
the process to terminate, it has no return value.</p>
</p></div>
<p><a name="exit-1"><span class="bold_code">exit(Reason)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Stops the execution of the calling process with the exit
reason <span class="code">Reason</span>, where <span class="code">Reason</span> is any term. Since
evaluating this function causes the process to terminate, it
has no return value.</p>
<div class="example"><pre>
> <span class="bold_code">exit(foobar).</span>
** exception exit: foobar
> <span class="bold_code">catch exit(foobar).</span>
{'EXIT',foobar}</pre></div>
</p></div>
<p><a name="exit-2"><span class="bold_code">exit(Pid, Reason) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sends an exit signal with exit reason <span class="code">Reason</span> to
the process <span class="code">Pid</span>.</p>
<p>The following behavior apply if <span class="code">Reason</span> is any term
except <span class="code">normal</span> or <span class="code">kill</span>:</p>
<p>If <span class="code">Pid</span> is not trapping exits, <span class="code">Pid</span> itself will
exit with exit reason <span class="code">Reason</span>. If <span class="code">Pid</span> is trapping
exits, the exit signal is transformed into a message
<span class="code">{'EXIT', From, Reason}</span> and delivered to the message
queue of <span class="code">Pid</span>. <span class="code">From</span> is the pid of the process
which sent the exit signal. See also
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>.</p>
<p>If <span class="code">Reason</span> is the atom <span class="code">normal</span>, <span class="code">Pid</span> will
not exit. If it is trapping exits, the exit signal is
transformed into a message <span class="code">{'EXIT', From, normal}</span>
and delivered to its message queue.</p>
<p>If <span class="code">Reason</span> is the atom <span class="code">kill</span>, that is if
<span class="code">exit(Pid, kill)</span> is called, an untrappable exit signal
is sent to <span class="code">Pid</span> which will unconditionally exit with
exit reason <span class="code">killed</span>.</p>
</p></div>
<p><a name="external_size-1"><span class="bold_code">erlang:external_size(Term) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Calculates, without doing the encoding, the maximum byte size for
a term encoded in the Erlang external term format. The following
condition applies always:</p>
<p>
<div class="example"><pre>
> <span class="bold_code">Size1 = byte_size(term_to_binary(Term)),</span>
> <span class="bold_code">Size2 = erlang:external_size(Term),</span>
> <span class="bold_code">true = Size1 =< Size2.</span>
true
</pre></div>
</p>
<p>This is equivalent to a call to: <div class="example"><pre>erlang:external_size(Term, [])
</pre></div></p>
</p></div>
<p><a name="external_size-2"><span class="bold_code">erlang:external_size(Term, [Option]) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = {minor_version, Version}</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Calculates, without doing the encoding, the maximum byte size for
a term encoded in the Erlang external term format. The following
condition applies always:</p>
<p>
<div class="example"><pre>
> <span class="bold_code">Size1 = byte_size(term_to_binary(Term, Options)),</span>
> <span class="bold_code">Size2 = erlang:external_size(Term, Options),</span>
> <span class="bold_code">true = Size1 =< Size2.</span>
true
</pre></div>
</p>
<p>The option <span class="code">{minor_version, Version}</span> specifies how floats
are encoded. See
<span class="bold_code"><a href="#term_to_binary-2">term_to_binary/2</a></span> for
a more detailed description.
</p>
</p></div>
<p><a name="float-1"><span class="bold_code">float(Number) -> float()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Number = number()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a float by converting <span class="code">Number</span> to a float.</p>
<div class="example"><pre>
> <span class="bold_code">float(55).</span>
55.0</pre></div>
<p>Allowed in guard tests.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Note that if used on the top-level in a guard, it will
test whether the argument is a floating point number; for
clarity, use
<span class="bold_code"><a href="#is_float-1">is_float/1</a></span> instead.</p>
<p>When <span class="code">float/1</span> is used in an expression in a guard,
such as '<span class="code">float(A) == 4.0</span>', it converts a number as
described above.</p>
</p></div>
</div>
</p></div>
<p><a name="float_to_list-1"><span class="bold_code">float_to_list(Float) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Float = float()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Float</span>.</p>
<div class="example"><pre>
> <span class="bold_code">float_to_list(7.0).</span>
"7.00000000000000000000e+00"</pre></div>
</p></div>
<p><a name="fun_info-1"></a><span class="bold_code">erlang:fun_info(Fun) -> [{Item, Info}]</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
<div class="REFTYPES"><span class="bold_code">Item = arity<br> | env<br> | index<br> | name<br> | module<br> | new_index<br> | new_uniq<br> | pid<br> | type<br> | uniq</span></div>
<div class="REFTYPES"><span class="bold_code">Info = term()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns a list containing information about the fun
<span class="code">Fun</span>. Each element of the list is a tuple. The order of
the tuples is not defined, and more tuples may be added in a
future release.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is mainly intended for debugging, but it can
occasionally be useful in library functions that might need
to verify, for instance, the arity of a fun.</p>
</p></div>
</div>
<p>There are two types of funs with slightly different
semantics:</p>
<p>A fun created by <span class="code">fun M:F/A</span> is called an
<strong>external</strong> fun. Calling it will always call the
function <span class="code">F</span> with arity <span class="code">A</span> in the latest code for
module <span class="code">M</span>. Note that module <span class="code">M</span> does not even need
to be loaded when the fun <span class="code">fun M:F/A</span> is created.</p>
<p>All other funs are called <strong>local</strong>. When a local fun
is called, the same version of the code that created the fun
will be called (even if newer version of the module has been
loaded).</p>
<p>The following elements will always be present in the list
for both local and external funs:</p>
<dl>
<dt><strong><span class="code">{type, Type}</span></strong></dt>
<dd>
<p><span class="code">Type</span> is either <span class="code">local</span> or <span class="code">external</span>.</p>
</dd>
<dt><strong><span class="code">{module, Module}</span></strong></dt>
<dd>
<p><span class="code">Module</span> (an atom) is the module name.</p>
<p>If <span class="code">Fun</span> is a local fun, <span class="code">Module</span> is the module
in which the fun is defined.</p>
<p>If <span class="code">Fun</span> is an external fun, <span class="code">Module</span> is the
module that the fun refers to.</p>
</dd>
<dt><strong><span class="code">{name, Name}</span></strong></dt>
<dd>
<p><span class="code">Name</span> (an atom) is a function name.</p>
<p>If <span class="code">Fun</span> is a local fun, <span class="code">Name</span> is the name
of the local function that implements the fun.
(This name was generated by the compiler, and is generally
only of informational use. As it is a local function, it
is not possible to call it directly.)
If no code is currently loaded for the fun, <span class="code">[]</span>
will be returned instead of an atom.</p>
<p>If <span class="code">Fun</span> is an external fun, <span class="code">Name</span> is the name
of the exported function that the fun refers to.</p>
</dd>
<dt><strong><span class="code">{arity, Arity}</span></strong></dt>
<dd>
<p><span class="code">Arity</span> is the number of arguments that the fun
should be called with.</p>
</dd>
<dt><strong><span class="code">{env, Env}</span></strong></dt>
<dd>
<p><span class="code">Env</span> (a list) is the environment or free variables
for the fun. (For external funs, the returned list is
always empty.)</p>
</dd>
</dl>
<p>The following elements will only be present in the list if
<span class="code">Fun</span> is local:</p>
<dl>
<dt><strong><span class="code">{pid, Pid}</span></strong></dt>
<dd>
<p><span class="code">Pid</span> is the pid of the process that originally
created the fun.</p>
</dd>
<dt><strong><span class="code">{index, Index}</span></strong></dt>
<dd>
<p><span class="code">Index</span> (an integer) is an index into the module's
fun table.</p>
</dd>
<dt><strong><span class="code">{new_index, Index}</span></strong></dt>
<dd>
<p><span class="code">Index</span> (an integer) is an index into the module's
fun table.</p>
</dd>
<dt><strong><span class="code">{new_uniq, Uniq}</span></strong></dt>
<dd>
<p><span class="code">Uniq</span> (a binary) is a unique value for this fun.
It is calculated from the compiled code for the entire module.</p>
</dd>
<dt><strong><span class="code">{uniq, Uniq}</span></strong></dt>
<dd>
<p><span class="code">Uniq</span> (an integer) is a unique value for this fun.
Starting in the R15 release, this integer is calculated from
the compiled code for the entire module. Before R15, this
integer was based on only the body of the fun.
</p>
</dd>
</dl>
</p></div>
<p><a name="fun_info-2"><span class="bold_code">erlang:fun_info(Fun, Item) -> {Item, Info}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Fun = fun()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item, Info -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns information about <span class="code">Fun</span> as specified by
<span class="code">Item</span>, in the form <span class="code">{Item,Info}</span>.</p>
<p>For any fun, <span class="code">Item</span> can be any of the atoms
<span class="code">module</span>, <span class="code">name</span>, <span class="code">arity</span>, <span class="code">env</span>, or <span class="code">type</span>.</p>
<p>For a local fun, <span class="code">Item</span> can also be any of the atoms
<span class="code">index</span>, <span class="code">new_index</span>, <span class="code">new_uniq</span>,
<span class="code">uniq</span>, and <span class="code">pid</span>. For an external fun, the value
of any of these items is always the atom <span class="code">undefined</span>.</p>
<p>See
<span class="bold_code"><a href="#fun_info-1">erlang:fun_info/1</a></span>.</p>
</p></div>
<p><a name="fun_to_list-1"><span class="bold_code">erlang:fun_to_list(Fun) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Fun = fun()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Fun</span>.</p>
</p></div>
<p><a name="function_exported-3"><span class="bold_code">erlang:function_exported(Module, Function, Arity) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Arity = arity()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if the module <span class="code">Module</span> is loaded
and contains an exported function <span class="code">Function/Arity</span>;
otherwise <span class="code">false</span>.</p>
<p>Returns <span class="code">false</span> for any BIF (functions implemented in C
rather than in Erlang).</p>
</p></div>
<p><a name="garbage_collect-0"><span class="bold_code">garbage_collect() -> true</span></a><br></p>
<div class="REFBODY"><p>
<p>Forces an immediate garbage collection of the currently
executing process. The function should not be used, unless
it has been noticed -- or there are good reasons to suspect --
that the spontaneous garbage collection will occur too late
or not at all. Improper use may seriously degrade system
performance.</p>
<p>Compatibility note: In versions of OTP prior to R7,
the garbage collection took place at the next context switch,
not immediately. To force a context switch after a call to
<span class="code">erlang:garbage_collect()</span>, it was sufficient to make
any function call.</p>
</p></div>
<p><a name="garbage_collect-1"><span class="bold_code">garbage_collect(Pid) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Works like <span class="code">erlang:garbage_collect()</span> but on any
process. The same caveats apply. Returns <span class="code">false</span> if
<span class="code">Pid</span> refers to a dead process; <span class="code">true</span> otherwise.</p>
</p></div>
<p><a name="get-0"><span class="bold_code">get() -> [{Key, Val}]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Key = Val = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the process dictionary as a list of
<span class="code">{Key, Val}</span> tuples.</p>
<div class="example"><pre>
> <span class="bold_code">put(key1, merry),</span>
<span class="bold_code">put(key2, lambs),</span>
<span class="bold_code">put(key3, {are, playing}),</span>
<span class="bold_code">get().</span>
[{key1,merry},{key2,lambs},{key3,{are,playing}}]</pre></div>
</p></div>
<p><a name="get-1"><span class="bold_code">get(Key) -> Val | undefined</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Key = Val = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the value <span class="code">Val</span>associated with <span class="code">Key</span> in
the process dictionary, or <span class="code">undefined</span> if <span class="code">Key</span>
does not exist.</p>
<div class="example"><pre>
> <span class="bold_code">put(key1, merry),</span>
<span class="bold_code">put(key2, lambs),</span>
<span class="bold_code">put({any, [valid, term]}, {are, playing}),</span>
<span class="bold_code">get({any, [valid, term]}).</span>
{are,playing}</pre></div>
</p></div>
<p><a name="get_cookie-0"></a><span class="bold_code">erlang:get_cookie() -> Cookie | nocookie</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Cookie = atom()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the magic cookie of the local node, if the node is
alive; otherwise the atom <span class="code">nocookie</span>.</p>
</p></div>
<p><a name="get_keys-1"><span class="bold_code">get_keys(Val) -> [Key]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Val = Key = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of keys which are associated with the value
<span class="code">Val</span> in the process dictionary.</p>
<div class="example"><pre>
> <span class="bold_code">put(mary, {1, 2}),</span>
<span class="bold_code">put(had, {1, 2}),</span>
<span class="bold_code">put(a, {1, 2}),</span>
<span class="bold_code">put(little, {1, 2}),</span>
<span class="bold_code">put(dog, {1, 3}),</span>
<span class="bold_code">put(lamb, {1, 2}),</span>
<span class="bold_code">get_keys({1, 2}).</span>
[mary,had,a,little,lamb]</pre></div>
</p></div>
<p><a name="get_stacktrace-0"><span class="bold_code">erlang:get_stacktrace() -> [{Module, Function, Arity | Args, Location}]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Arity = arity()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Args = [term()]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Location = [{atom(),term()}]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Get the call stack back-trace (<strong>stacktrace</strong>) of the last
exception in the calling process as a list of
<span class="code">{Module,Function,Arity,Location}</span> tuples.
The <span class="code">Arity</span> field in the first tuple may be the argument
list of that function call instead of an arity integer,
depending on the exception.</p>
<p>If there has not been any exceptions in a process, the
stacktrace is []. After a code change for the process,
the stacktrace may also be reset to [].</p>
<p>The stacktrace is the same data as the <span class="code">catch</span> operator
returns, for example:</p>
<p><span class="code">{'EXIT',{badarg,Stacktrace}} = catch abs(x)</span></p>
<p><span class="code">Location</span> is a (possibly empty) list of two-tuples that
may indicate the location in the source code of the function.
The first element is an atom that describes the type of
information in the second element. Currently the following
items may occur:</p>
<dl>
<dt><strong><span class="code">file</span></strong></dt>
<dd>
<p>The second element of the tuple is a string (list of
characters) representing the filename of the source file
of the function.</p>
</dd>
<dt><strong><span class="code">line</span></strong></dt>
<dd>
<p>The second element of the tuple is the line number
(an integer greater than zero) in the source file
where the exception occurred or the function was called.</p>
</dd>
</dl>
<p>See also
<span class="bold_code"><a href="#error-1">erlang:error/1</a></span> and
<span class="bold_code"><a href="#error-2">erlang:error/2</a></span>.</p>
</p></div>
<p><a name="group_leader-0"><span class="bold_code">group_leader() -> GroupLeader</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">GroupLeader = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the pid of the group leader for the process which
evaluates the function.</p>
<p>Every process is a member of some process group and all
groups have a <strong>group leader</strong>. All IO from the group
is channeled to the group leader. When a new process is
spawned, it gets the same group leader as the spawning
process. Initially, at system start-up, <span class="code">init</span> is both
its own group leader and the group leader of all processes.</p>
</p></div>
<p><a name="group_leader-2"><span class="bold_code">group_leader(GroupLeader, Pid) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">GroupLeader = Pid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets the group leader of <span class="code">Pid</span> to <span class="code">GroupLeader</span>.
Typically, this is used when a processes started from a
certain shell should have another group leader than
<span class="code">init</span>.</p>
<p>See also
<span class="bold_code"><a href="#group_leader-0">group_leader/0</a></span>.</p>
</p></div>
<p><a name="halt-0"><span class="bold_code">halt()</span></a><br></p>
<div class="REFBODY"><p>
<p>The same as
<span class="bold_code"><a href="#halt-2"><span class="code">halt(0, [])</span></a></span>.</p>
<div class="example"><pre>
> <span class="bold_code">halt().</span>
os_prompt% </pre></div>
</p></div>
<p><a name="halt-1"><span class="bold_code">halt(Status)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Status = integer() >= 0 | string() | abort</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The same as
<span class="bold_code"><a href="#halt-2"><span class="code">halt(Status, [])</span></a></span>.</p>
<div class="example"><pre>
> <span class="bold_code">halt(17).</span>
os_prompt% <span class="bold_code">echo $?</span>
17
os_prompt% </pre></div>
</p></div>
<p><a name="halt-2"><span class="bold_code">halt(Status, Options)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Status = integer() >= 0 | string() | abort</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Options = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = {flush,boolean()} | term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">Status</span> must be a non-negative integer, a string,
or the atom <span class="code">abort</span>.
Halts the Erlang runtime system. Has no return value.
Depending on <span class="code">Status</span>:
</p>
<dl>
<dt><strong>integer()</strong></dt>
<dd>The runtime system exits with the integer value <span class="code">Status</span>
as status code to the calling environment (operating system).
</dd>
<dt><strong>string()</strong></dt>
<dd>An erlang crash dump is produced with <span class="code">Status</span> as slogan,
and then the runtime system exits with status code <span class="code">1</span>.
</dd>
<dt><strong><span class="code">abort</span></strong></dt>
<dd>
The runtime system aborts producing a core dump, if that is
enabled in the operating system.
</dd>
</dl>
<p>Note that on many platforms, only the status codes 0-255 are
supported by the operating system.
</p>
<p>For integer <span class="code">Status</span> the Erlang runtime system closes all ports
and allows async threads to finish their operations before exiting.
To exit without such flushing use
<span class="code">Option</span> as <span class="code">{flush,false}</span>.
</p>
<p>For statuses <span class="code">string()</span> and <span class="code">abort</span> the <span class="code">flush</span>
option is ignored and flushing is <strong>not</strong> done.
</p>
</p></div>
<p><a name="hash-2"><span class="bold_code">erlang:hash(Term, Range) -> Hash</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns a hash value for <span class="code">Term</span> within the range
<span class="code">1..Range</span>. The allowed range is 1..2^27-1.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is deprecated as the hash value may differ on
different architectures. Also the hash values for integer
terms larger than 2^27 as well as large binaries are very
poor. The BIF is retained for backward compatibility
reasons (it may have been used to hash records into a file),
but all new code should use one of the BIFs
<span class="code">erlang:phash/2</span> or <span class="code">erlang:phash2/1,2</span> instead.</p>
</p></div>
</div>
</p></div>
<p><a name="hd-1"><span class="bold_code">hd(List) -> term()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">List = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the head of <span class="code">List</span>, that is, the first element.</p>
<div class="example"><pre>
> <span class="bold_code">hd([1,2,3,4,5]).</span>
1</pre></div>
<p>Allowed in guard tests.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">List</span> is the empty list [].</p>
</p></div>
<p><a name="hibernate-3"><span class="bold_code">erlang:hibernate(Module, Function, Args)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Args = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Puts the calling process into a wait state where its memory
allocation has been reduced as much as possible, which is
useful if the process does not expect to receive any messages
in the near future.</p>
<p>The process will be awaken when a message is sent to it, and
control will resume in <span class="code">Module:Function</span> with
the arguments given by <span class="code">Args</span> with the call stack
emptied, meaning that the process will terminate when that
function returns. Thus <span class="code">erlang:hibernate/3</span> will never
return to its caller.</p>
<p>If the process has any message in its message queue,
the process will be awaken immediately in the same way as
described above.</p>
<p>In more technical terms, what <span class="code">erlang:hibernate/3</span> does
is the following. It discards the call stack for the process.
Then it garbage collects the process. After the garbage
collection, all live data is in one continuous heap. The heap
is then shrunken to the exact same size as the live data
which it holds (even if that size is less than the minimum
heap size for the process).</p>
<p>If the size of the live data in the process is less than
the minimum heap size, the first garbage collection occurring
after the process has been awaken will ensure that the heap
size is changed to a size not smaller than the minimum heap
size.</p>
<p>Note that emptying the call stack means that any surrounding
<span class="code">catch</span> is removed and has to be re-inserted after
hibernation. One effect of this is that processes started
using <span class="code">proc_lib</span> (also indirectly, such as
<span class="code">gen_server</span> processes), should use
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','proc_lib.html#hibernate-3');">proc_lib:hibernate/3</a></span>
instead to ensure that the exception handler continues to work
when the process wakes up.</p>
</p></div>
<p><a name="integer_to_list-1"><span class="bold_code">integer_to_list(Integer) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Integer = integer()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Integer</span>.</p>
<div class="example"><pre>
> <span class="bold_code">integer_to_list(77).</span>
"77"</pre></div>
</p></div>
<p><a name="integer_to_list-2"></a><span class="bold_code">integer_to_list(Integer, Base) -> string()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Integer = integer()</span></div>
<div class="REFTYPES"><span class="bold_code">Base = 2..36</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Integer</span> in base <span class="code">Base</span>.</p>
<div class="example"><pre>
> <span class="bold_code">integer_to_list(1023, 16).</span>
"3FF"</pre></div>
</p></div>
<p><a name="iolist_to_binary-1"><span class="bold_code">iolist_to_binary(IoListOrBinary) -> binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoListOrBinary = iolist() | binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a binary which is made from the integers and
binaries in <span class="code">IoListOrBinary</span>.</p>
<div class="example"><pre>
> <span class="bold_code">Bin1 = <<1,2,3>>.</span>
<<1,2,3>>
> <span class="bold_code">Bin2 = <<4,5>>.</span>
<<4,5>>
> <span class="bold_code">Bin3 = <<6>>.</span>
<<6>>
> <span class="bold_code">iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).</span>
<<1,2,3,1,2,3,4,5,4,6>></pre></div>
</p></div>
<p><a name="iolist_size-1"><span class="bold_code">iolist_size(Item) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Item = iolist() | binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer which is the size in bytes
of the binary that would be the result of
<span class="code">iolist_to_binary(Item)</span>.</p>
<div class="example"><pre>
> <span class="bold_code">iolist_size([1,2|<<3,4>>]).</span>
4</pre></div>
</p></div>
<p><a name="is_alive-0"><span class="bold_code">is_alive() -> boolean()</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if the local node is alive; that is, if
the node can be part of a distributed system. Otherwise, it
returns <span class="code">false</span>.</p>
</p></div>
<p><a name="is_atom-1"><span class="bold_code">is_atom(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is an atom;
otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_binary-1"><span class="bold_code">is_binary(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a binary;
otherwise returns <span class="code">false</span>.</p>
<p>A binary always contains a complete number of bytes.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_bitstring-1"><span class="bold_code">is_bitstring(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a bitstring (including a binary);
otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_boolean-1"><span class="bold_code">is_boolean(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is
either the atom <span class="code">true</span> or the atom <span class="code">false</span>
(i.e. a boolean); otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_builtin-3"><span class="bold_code">erlang:is_builtin(Module, Function, Arity) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Arity = arity()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Module:Function/Arity</span> is
a BIF implemented in C; otherwise returns <span class="code">false</span>.
This BIF is useful for builders of cross reference tools.</p>
</p></div>
<p><a name="is_float-1"><span class="bold_code">is_float(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a floating point
number; otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_function-1"><span class="bold_code">is_function(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a fun; otherwise
returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_function-2"><span class="bold_code">is_function(Term, Arity) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Arity = arity()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a fun that can be
applied with <span class="code">Arity</span> number of arguments; otherwise
returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>Currently, <span class="code">is_function/2</span> will also return
<span class="code">true</span> if the first argument is a tuple fun (a tuple
containing two atoms). In a future release, tuple funs will
no longer be supported and <span class="code">is_function/2</span> will return
<span class="code">false</span> if given a tuple fun.</p>
</p></div>
</div>
</p></div>
<p><a name="is_integer-1"><span class="bold_code">is_integer(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is an integer;
otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_list-1"><span class="bold_code">is_list(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a list with
zero or more elements; otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_number-1"><span class="bold_code">is_number(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is either an integer or a
floating point number; otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_pid-1"><span class="bold_code">is_pid(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a pid (process
identifier); otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_port-1"><span class="bold_code">is_port(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a port identifier;
otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_process_alive-1"><span class="bold_code">is_process_alive(Pid) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>
<span class="code">Pid</span> must refer to a process at the local node.
Returns <span class="code">true</span> if the process exists and is alive, that
is, is not exiting and has not exited. Otherwise, returns
<span class="code">false</span>.
</p>
</p></div>
<p><a name="is_record-2"><span class="bold_code">is_record(Term, RecordTag) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">RecordTag = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a tuple and its first
element is <span class="code">RecordTag</span>. Otherwise, returns <span class="code">false</span>.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Normally the compiler treats calls to <span class="code">is_record/2</span>
specially. It emits code to verify that <span class="code">Term</span> is a
tuple, that its first element is <span class="code">RecordTag</span>, and that
the size is correct. However, if the <span class="code">RecordTag</span> is
not a literal atom, the <span class="code">is_record/2</span> BIF will be
called instead and the size of the tuple will not be
verified.</p>
</p></div>
</div>
<p>Allowed in guard tests, if <span class="code">RecordTag</span> is a literal
atom.</p>
</p></div>
<p><a name="is_record-3"><span class="bold_code">is_record(Term, RecordTag, Size) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">RecordTag = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Size = integer()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">RecordTag</span> must be an atom. Returns <span class="code">true</span> if
<span class="code">Term</span> is a tuple, its first element is <span class="code">RecordTag</span>,
and its size is <span class="code">Size</span>. Otherwise, returns <span class="code">false</span>.</p>
<p>Allowed in guard tests, provided that <span class="code">RecordTag</span> is
a literal atom and <span class="code">Size</span> is a literal integer.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>This BIF is documented for completeness. In most cases
<span class="code">is_record/2</span> should be used.</p>
</p></div>
</div>
</p></div>
<p><a name="is_reference-1"><span class="bold_code">is_reference(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a reference;
otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="is_tuple-1"><span class="bold_code">is_tuple(Term) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if <span class="code">Term</span> is a tuple;
otherwise returns <span class="code">false</span>.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="length-1"><span class="bold_code">length(List) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">List = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the length of <span class="code">List</span>.</p>
<div class="example"><pre>
> <span class="bold_code">length([1,2,3,4,5,6,7,8,9]).</span>
9</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="link-1"><span class="bold_code">link(Pid) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid() | port()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Creates a link between the calling process and another
process (or port) <span class="code">Pid</span>, if there is not such a link
already. If a process attempts to create a link to itself,
nothing is done. Returns <span class="code">true</span>.</p>
<p>If <span class="code">Pid</span> does not exist, the behavior of the BIF depends
on if the calling process is trapping exits or not (see
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>):</p>
<ul>
<li>If the calling process is not trapping exits, and
checking <span class="code">Pid</span> is cheap -- that is, if <span class="code">Pid</span> is
local -- <span class="code">link/1</span> fails with reason <span class="code">noproc</span>.</li>
<li>Otherwise, if the calling process is trapping exits,
and/or <span class="code">Pid</span> is remote, <span class="code">link/1</span> returns
<span class="code">true</span>, but an exit signal with reason <span class="code">noproc</span>
is sent to the calling process.</li>
</ul>
</p></div>
<p><a name="list_to_atom-1"><span class="bold_code">list_to_atom(String) -> atom()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">String = string()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the atom whose text representation is <span class="code">String</span>.</p>
<div class="example"><pre>
> <span class="bold_code">list_to_atom("Erlang").</span>
'Erlang'</pre></div>
</p></div>
<p><a name="list_to_binary-1"><span class="bold_code">list_to_binary(IoList) -> binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoList = iolist()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a binary which is made from the integers and
binaries in <span class="code">IoList</span>.</p>
<div class="example"><pre>
> <span class="bold_code">Bin1 = <<1,2,3>>.</span>
<<1,2,3>>
> <span class="bold_code">Bin2 = <<4,5>>.</span>
<<4,5>>
> <span class="bold_code">Bin3 = <<6>>.</span>
<<6>>
> <span class="bold_code">list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).</span>
<<1,2,3,1,2,3,4,5,4,6>></pre></div>
</p></div>
<p><a name="list_to_bitstring-1"><span class="bold_code">list_to_bitstring(BitstringList) -> bitstring()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">BitstringList = [BitstringList | bitstring() | char()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a bitstring which is made from the integers and
bitstrings in <span class="code">BitstringList</span>. (The last tail in <span class="code">BitstringList</span>
is allowed to be a bitstring.)</p>
<div class="example"><pre>
> <span class="bold_code">Bin1 = <<1,2,3>>.</span>
<<1,2,3>>
> <span class="bold_code">Bin2 = <<4,5>>.</span>
<<4,5>>
> <span class="bold_code">Bin3 = <<6,7:4,>>.</span>
<<6>>
> <span class="bold_code">list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).</span>
<<1,2,3,1,2,3,4,5,4,6,7:46>></pre></div>
</p></div>
<p><a name="list_to_existing_atom-1"><span class="bold_code">list_to_existing_atom(String) -> atom()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">String = string()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the atom whose text representation is <span class="code">String</span>,
but only if there already exists such atom.</p>
<p>Failure: <span class="code">badarg</span> if there does not already exist an atom
whose text representation is <span class="code">String</span>.</p>
</p></div>
<p><a name="list_to_float-1"><span class="bold_code">list_to_float(String) -> float()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">String = string()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the float whose text representation is <span class="code">String</span>.</p>
<div class="example"><pre>
> <span class="bold_code">list_to_float("2.2017764e+0").</span>
2.2017764</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">String</span> contains a bad
representation of a float.</p>
</p></div>
<p><a name="list_to_integer-1"><span class="bold_code">list_to_integer(String) -> integer()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">String = string()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer whose text representation is
<span class="code">String</span>.</p>
<div class="example"><pre>
> <span class="bold_code">list_to_integer("123").</span>
123</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">String</span> contains a bad
representation of an integer.</p>
</p></div>
<p><a name="list_to_integer-2"></a><span class="bold_code">list_to_integer(String, Base) -> integer()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">String = string()</span></div>
<div class="REFTYPES"><span class="bold_code">Base = 2..36</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns an integer whose text representation in base
<span class="code">Base</span> is <span class="code">String</span>.</p>
<div class="example"><pre>
> <span class="bold_code">list_to_integer("3FF", 16).</span>
1023</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">String</span> contains a bad
representation of an integer.</p>
</p></div>
<p><a name="list_to_pid-1"><span class="bold_code">list_to_pid(String) -> pid()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">String = string()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a pid whose text representation is <span class="code">String</span>.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.</p>
</p></div>
</div>
<div class="example"><pre>
> <span class="bold_code">list_to_pid("<0.4.1>").</span>
<0.4.1></pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">String</span> contains a bad
representation of a pid.</p>
</p></div>
<p><a name="list_to_tuple-1"><span class="bold_code">list_to_tuple(List) -> tuple()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">List = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a tuple which corresponds to <span class="code">List</span>. <span class="code">List</span>
can contain any Erlang terms.</p>
<div class="example"><pre>
> <span class="bold_code">list_to_tuple([share, ['Ericsson_B', 163]]).</span>
{share, ['Ericsson_B', 163]}</pre></div>
</p></div>
<p><a name="load_module-2"><span class="bold_code">load_module(Module, Binary) -> {module, Module} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Binary = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = badfile | not_purged | badfile</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>If <span class="code">Binary</span> contains the object code for the module
<span class="code">Module</span>, this BIF loads that object code. Also, if
the code for the module <span class="code">Module</span> already exists, all
export references are replaced so they point to the newly
loaded code. The previously loaded code is kept in the system
as old code, as there may still be processes which are
executing that code. It returns either
<span class="code">{module, Module}</span>, or <span class="code">{error, Reason}</span> if loading
fails. <span class="code">Reason</span> is one of the following:</p>
<dl>
<dt><strong><span class="code">badfile</span></strong></dt>
<dd>
<p>The object code in <span class="code">Binary</span> has an incorrect format.</p>
</dd>
<dt><strong><span class="code">not_purged</span></strong></dt>
<dd>
<p><span class="code">Binary</span> contains a module which cannot be loaded
because old code for this module already exists.</p>
</dd>
<dt><strong><span class="code">badfile</span></strong></dt>
<dd>
<p>The object code contains code for another module than
<span class="code">Module</span></p>
</dd>
</dl>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for the code server (see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>) and should not be
used elsewhere.</p>
</p></div>
</div>
</p></div>
<p><a name="load_nif-2"><span class="bold_code">erlang:load_nif(Path, LoadInfo) -> ok | {error, {Reason, Text}}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Path = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">LoadInfo = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = load_failed | bad_lib | load | reload |
upgrade | old_code</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Text = string()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>In releases older than OTP R14B, NIFs were an
experimental feature. Versions of OTP older than R14B might
have different and possibly incompatible NIF semantics and
interfaces. For example, in R13B03 the return value on
failure was
<span class="code">{error,Reason,Text}</span>.</p>
</p></div>
</div>
<p>Loads and links a dynamic library containing native
implemented functions (NIFs) for a module. <span class="code">Path</span> is a
file path to the sharable object/dynamic library file minus
the OS-dependent file extension (.so for Unix and .dll for
Windows). See <span class="bold_code"><a href="erl_nif.html">erl_nif</a></span>
on how to implement a NIF library.</p>
<p><span class="code">LoadInfo</span> can be any term. It will be passed on to
the library as part of the initialization. A good practice is
to include a module version number to support future code
upgrade scenarios.</p>
<p>The call to <span class="code">load_nif/2</span> must be made
<strong>directly</strong> from the Erlang code of the module that the
NIF library belongs to.</p>
<p>It returns either <span class="code">ok</span>, or <span class="code">{error,{Reason,Text}}</span>
if loading fails. <span class="code">Reason</span> is one of the atoms below,
while <span class="code">Text</span> is a human readable string that may give
some more information about the failure.</p>
<dl>
<dt><strong><span class="code">load_failed</span></strong></dt>
<dd>
<p>The OS failed to load the NIF library.</p>
</dd>
<dt><strong><span class="code">bad_lib</span></strong></dt>
<dd>
<p>The library did not fulfil the requirements as a NIF
library of the calling module.</p>
</dd>
<dt><strong><span class="code">load | reload | upgrade</span></strong></dt>
<dd>
<p>The corresponding library callback was not successful.</p>
</dd>
<dt><strong><span class="code">old_code</span></strong></dt>
<dd>
<p>The call to <span class="code">load_nif/2</span> was made from the old
code of a module that has been upgraded. This is not
allowed.</p>
</dd>
</dl>
</p></div>
<p><a name="loaded-0"><span class="bold_code">erlang:loaded() -> [Module]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of all loaded Erlang modules (current and/or
old code), including preloaded modules.</p>
<p>See also <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>.</p>
</p></div>
<p><a name="localtime-0"><span class="bold_code">erlang:localtime() -> DateTime</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">DateTime = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-datetime');">calendar:datetime()</a></span></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the current local date and time
<span class="code">{{Year, Month, Day}, {Hour, Minute, Second}}</span>.</p>
<p>The time zone and daylight saving time correction depend
on the underlying OS.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:localtime().</span>
{{1996,11,6},{14,45,17}}</pre></div>
</p></div>
<p><a name="localtime_to_universaltime-1"></a><span class="bold_code">erlang:localtime_to_universaltime(Localtime :: {Date1, Time1}) -><br> {Date2, Time2}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Date1 = Date2 = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-date');">calendar:date()</a></span></span></div>
<div class="REFTYPES"><span class="bold_code"></span></div>
<div class="REFTYPES"><span class="bold_code">Time1 = Time2 = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-time');">calendar:time()</a></span></span></div>
<div class="REFTYPES"><span class="bold_code"></span></div>
</div></p>
<div class="REFBODY"><p>
<p>Converts local date and time to Universal Time Coordinated
(UTC), if this is supported by the underlying OS. Otherwise,
no conversion is done and <span class="code">{Date1, Time1}</span> is returned.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).</span>
{{1996,11,6},{13,45,17}}</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">Date1</span> or <span class="code">Time1</span> do
not denote a valid date or time.</p>
</p></div>
<p><a name="localtime_to_universaltime-2"><span class="bold_code">erlang:localtime_to_universaltime({Date1, Time1}, IsDst) -> {Date2, Time2}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Date1 = Date2 = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-date');">calendar:date()</a></span></span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Time1 = Time2 = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-time');">calendar:time()</a></span></span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">IsDst = true | false | undefined</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Converts local date and time to Universal Time Coordinated
(UTC) just like <span class="code">erlang:localtime_to_universaltime/1</span>,
but the caller decides if daylight saving time is active or
not.</p>
<p>If <span class="code">IsDst == true</span> the <span class="code">{Date1, Time1}</span> is during
daylight saving time, if <span class="code">IsDst == false</span> it is not,
and if <span class="code">IsDst == undefined</span> the underlying OS may
guess, which is the same as calling
<span class="code">erlang:localtime_to_universaltime({Date1, Time1})</span>.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).</span>
{{1996,11,6},{12,45,17}}
> <span class="bold_code">erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).</span>
{{1996,11,6},{13,45,17}}
> <span class="bold_code">erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).</span>
{{1996,11,6},{13,45,17}}</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">Date1</span> or <span class="code">Time1</span> do
not denote a valid date or time.</p>
</p></div>
<p><a name="make_ref-0"><span class="bold_code">make_ref() -> reference()</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns an almost unique reference.</p>
<p>The returned reference will re-occur after approximately 2^82
calls; therefore it is unique enough for practical purposes.</p>
<div class="example"><pre>
> <span class="bold_code">make_ref().</span>
#Ref<0.0.0.135></pre></div>
</p></div>
<p><a name="make_tuple-2"><span class="bold_code">erlang:make_tuple(Arity, InitialValue) -> tuple()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Arity = arity()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InitialValue = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a new tuple of the given <span class="code">Arity</span>, where all
elements are <span class="code">InitialValue</span>.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:make_tuple(4, []).</span>
{[],[],[],[]}</pre></div>
</p></div>
<p><a name="make_tuple-3"><span class="bold_code">erlang:make_tuple(Arity, Default, InitList) -> tuple()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Arity = arity()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Default = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InitList = [{Position,term()}]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Position = integer()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">erlang:make_tuple</span> first creates a tuple of size <span class="code">Arity</span>
where each element has the value <span class="code">Default</span>. It then fills
in values from <span class="code">InitList</span>. Each list element in <span class="code">InitList</span>
must be a two-tuple where the first element is a position in the
newly created tuple and the second element is any term. If a position
occurs more than once in the list, the term corresponding to
last occurrence will be used.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).</span>
{{[],aa,[],[],zz}</pre></div>
</p></div>
<p><a name="max-2"></a><span class="bold_code">max(Term1, Term2) -> Maximum</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Term1 = Term2 = Maximum = term()</span></div>
<div class="REFTYPES"><span class="bold_code"></span></div>
<div class="REFTYPES"><span class="bold_code"></span></div>
</div></p>
<div class="REFBODY"><p>
<p>Return the largest of <span class="code">Term1</span> and <span class="code">Term2</span>;
if the terms compare equal, <span class="code">Term1</span> will be returned.</p>
</p></div>
<p><a name="md5-1"><span class="bold_code">erlang:md5(Data) -> Digest</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Digest = binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Computes an <span class="code">MD5</span> message digest from <span class="code">Data</span>, where
the length of the digest is 128 bits (16 bytes). <span class="code">Data</span>
is a binary or a list of small integers and binaries.</p>
<p>See The MD5 Message Digest Algorithm (RFC 1321) for more
information about MD5.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p><p>The MD5 Message Digest Algorithm is <strong>not</strong> considered
safe for code-signing or software integrity purposes.</p></p></div>
</div>
</p></div>
<p><a name="md5_final-1"><span class="bold_code">erlang:md5_final(Context) -> Digest</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Context = Digest = binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Finishes the update of an MD5 <span class="code">Context</span> and returns
the computed <span class="code">MD5</span> message digest.</p>
</p></div>
<p><a name="md5_init-0"><span class="bold_code">erlang:md5_init() -> Context</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Context = binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Creates an MD5 context, to be used in subsequent calls to
<span class="code">md5_update/2</span>.</p>
</p></div>
<p><a name="md5_update-2"><span class="bold_code">erlang:md5_update(Context, Data) -> NewContext</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Context = NewContext = binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Updates an MD5 <span class="code">Context</span> with <span class="code">Data</span>, and returns
a <span class="code">NewContext</span>.</p>
</p></div>
<p><a name="memory-0"><span class="bold_code">erlang:memory() -> [{Type, Size}]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Type, Size -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list containing information about memory
dynamically allocated by the Erlang emulator. Each element of
the list is a tuple <span class="code">{Type, Size}</span>. The first element
<span class="code">Type</span>is an atom describing memory type. The second
element <span class="code">Size</span>is memory size in bytes. A description of
each memory type follows:</p>
<dl>
<dt><strong><span class="code">total</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated, which is
the same as the sum of memory size for <span class="code">processes</span>
and <span class="code">system</span>.</p>
</dd>
<dt><strong><span class="code">processes</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated by
the Erlang processes.</p>
</dd>
<dt><strong><span class="code">processes_used</span></strong></dt>
<dd>
<p>The total amount of memory currently used by the Erlang
processes.</p>
<p>This memory is part of the memory presented as
<span class="code">processes</span> memory.</p>
</dd>
<dt><strong><span class="code">system</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated by
the emulator that is not directly related to any Erlang
process.</p>
<p>Memory presented as <span class="code">processes</span> is not included in
this memory.</p>
</dd>
<dt><strong><span class="code">atom</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated for atoms.</p>
<p>This memory is part of the memory presented as
<span class="code">system</span> memory.</p>
</dd>
<dt><strong><span class="code">atom_used</span></strong></dt>
<dd>
<p>The total amount of memory currently used for atoms.</p>
<p>This memory is part of the memory presented as
<span class="code">atom</span> memory.</p>
</dd>
<dt><strong><span class="code">binary</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated for
binaries.</p>
<p>This memory is part of the memory presented as
<span class="code">system</span> memory.</p>
</dd>
<dt><strong><span class="code">code</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated for
Erlang code.</p>
<p>This memory is part of the memory presented as
<span class="code">system</span> memory.</p>
</dd>
<dt><strong><span class="code">ets</span></strong></dt>
<dd>
<p>The total amount of memory currently allocated for ets
tables.</p>
<p>This memory is part of the memory presented as
<span class="code">system</span> memory.</p>
</dd>
<dt><strong><span class="code">maximum</span></strong></dt>
<dd>
<p>The maximum total amount of memory allocated since
the emulator was started.</p>
<p>This tuple is only present when the emulator is run with
instrumentation.</p>
<p>For information on how to run the emulator with
instrumentation see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','tools','instrument.html');">instrument(3)</a></span>
and/or <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html');">erl(1)</a></span>.</p>
</dd>
<dt><strong><span class="code">low</span></strong></dt>
<dd>
<p>Only on 64-bit halfword emulator.</p>
<p>The total amount of memory allocated in low memory areas
that are restricted to less than 4 Gb even though
the system may have more physical memory.</p>
<p>May be removed in future releases of halfword emulator.</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The <span class="code">system</span> value is not complete. Some allocated
memory that should be part of the <span class="code">system</span> value are
not.</p>
<p>When the emulator is run with instrumentation,
the <span class="code">system</span> value is more accurate, but memory
directly allocated by <span class="code">malloc</span> (and friends) are still
not part of the <span class="code">system</span> value. Direct calls to
<span class="code">malloc</span> are only done from OS specific runtime
libraries and perhaps from user implemented Erlang drivers
that do not use the memory allocation functions in
the driver interface.</p>
<p>Since the <span class="code">total</span> value is the sum of <span class="code">processes</span>
and <span class="code">system</span> the error in <span class="code">system</span> will propagate
to the <span class="code">total</span> value.</p>
<p>The different amounts of memory that are summed are
<strong>not</strong> gathered atomically which also introduce
an error in the result.</p>
</p></div>
</div>
<p>The different values has the following relation to each
other. Values beginning with an uppercase letter is not part
of the result.</p>
<div class="example"><pre>
total = processes + system
processes = processes_used + ProcessesNotUsed
system = atom + binary + code + ets + OtherSystem
atom = atom_used + AtomNotUsed
RealTotal = processes + RealSystem
RealSystem = system + MissedSystem</pre></div>
<p>More tuples in the returned list may be added in the future.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The <span class="code">total</span> value is supposed to be the total amount
of memory dynamically allocated by the emulator. Shared
libraries, the code of the emulator itself, and
the emulator stack(s) are not supposed to be included. That
is, the <span class="code">total</span> value is <strong>not</strong> supposed to be
equal to the total size of all pages mapped to the emulator.
Furthermore, due to fragmentation and pre-reservation of
memory areas, the size of the memory segments which contain
the dynamically allocated memory blocks can be substantially
larger than the total size of the dynamically allocated
memory blocks.</p>
</p></div>
</div>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>
Since erts version 5.6.4 <span class="code">erlang:memory/0</span> requires that
all <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>
allocators are enabled (default behaviour).
</p>
</p></div>
</div>
<p>Failure:</p>
<dl>
<dt><strong><span class="code">notsup</span></strong></dt>
<dd>
If an <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>
allocator has been disabled.
</dd>
</dl>
</p></div>
<p><a name="memory-1"><span class="bold_code">erlang:memory(Type | [Type]) -> Size | [{Type, Size}]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Type, Size -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the memory size in bytes allocated for memory of
type <span class="code">Type</span>. The argument can also be given as a list
of <span class="code">Type</span> atoms, in which case a corresponding list of
<span class="code">{Type, Size}</span> tuples is returned.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>
Since erts version 5.6.4 <span class="code">erlang:memory/1</span> requires that
all <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>
allocators are enabled (default behaviour).
</p>
</p></div>
</div>
<p>Failures:</p>
<dl>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Type</span> is not one of the memory types listed in the
documentation of
<span class="bold_code"><a href="#memory-0">erlang:memory/0</a></span>.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">maximum</span> is passed as <span class="code">Type</span> and the emulator
is not run in instrumented mode.
</dd>
<dt><strong><span class="code">notsup</span></strong></dt>
<dd>
If an <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>
allocator has been disabled.
</dd>
</dl>
<p>See also
<span class="bold_code"><a href="#memory-0">erlang:memory/0</a></span>.</p>
</p></div>
<p><a name="min-2"></a><span class="bold_code">min(Term1, Term2) -> Minimum</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Term1 = Term2 = Minimum = term()</span></div>
<div class="REFTYPES"><span class="bold_code"></span></div>
<div class="REFTYPES"><span class="bold_code"></span></div>
</div></p>
<div class="REFBODY"><p>
<p>Return the smallest of <span class="code">Term1</span> and <span class="code">Term2</span>;
if the terms compare equal, <span class="code">Term1</span> will be returned.</p>
</p></div>
<p><a name="module_loaded-1"><span class="bold_code">module_loaded(Module) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">true</span> if the module <span class="code">Module</span> is loaded,
otherwise returns <span class="code">false</span>. It does not attempt to load
the module.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for the code server (see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>) and should not be
used elsewhere.</p>
</p></div>
</div>
</p></div>
<p><a name="monitor-2"><span class="bold_code">monitor(Type, Item) -> MonitorRef</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Type = process</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item = pid() | {RegName, Node} | RegName</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> RegName = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Node = node()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">MonitorRef = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The calling process starts monitoring <span class="code">Item</span> which is
an object of type <span class="code">Type</span>.</p>
<p>Currently only processes can be monitored, i.e. the only
allowed <span class="code">Type</span> is <span class="code">process</span>, but other types may be
allowed in the future.</p>
<p><span class="code">Item</span> can be:</p>
<dl>
<dt><strong><span class="code">pid()</span></strong></dt>
<dd>
<p>The pid of the process to monitor.</p>
</dd>
<dt><strong><span class="code">{RegName, Node}</span></strong></dt>
<dd>
<p>A tuple consisting of a registered name of a process and
a node name. The process residing on the node <span class="code">Node</span>
with the registered name <span class="code">RegName</span> will be monitored.</p>
</dd>
<dt><strong><span class="code">RegName</span></strong></dt>
<dd>
<p>The process locally registered as <span class="code">RegName</span> will be
monitored.</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>When a process is monitored by registered name, the process
that has the registered name at the time when
<span class="code">monitor/2</span> is called will be monitored.
The monitor will not be effected, if the registered name is
unregistered.</p>
</p></div>
</div>
<p>A <span class="code">'DOWN'</span> message will be sent to the monitoring
process if <span class="code">Item</span> dies, if <span class="code">Item</span> does not exist,
or if the connection is lost to the node which <span class="code">Item</span>
resides on. A <span class="code">'DOWN'</span> message has the following pattern:</p>
<div class="example"><pre>
{'DOWN', MonitorRef, Type, Object, Info}</pre></div>
<p>where <span class="code">MonitorRef</span> and <span class="code">Type</span> are the same as
described above, and:</p>
<dl>
<dt><strong><span class="code">Object</span></strong></dt>
<dd>
<p>A reference to the monitored object:</p>
<ul>
<li>the pid of the monitored process, if <span class="code">Item</span> was
specified as a pid.</li>
<li>
<span class="code">{RegName, Node}</span>, if <span class="code">Item</span> was specified as
<span class="code">{RegName, Node}</span>.</li>
<li>
<span class="code">{RegName, Node}</span>, if <span class="code">Item</span> was specified as
<span class="code">RegName</span>. <span class="code">Node</span> will in this case be the
name of the local node (<span class="code">node()</span>).</li>
</ul>
</dd>
<dt><strong><span class="code">Info</span></strong></dt>
<dd>
<p>Either the exit reason of the process, <span class="code">noproc</span>
(non-existing process), or <span class="code">noconnection</span> (no
connection to <span class="code">Node</span>).</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>If/when <span class="code">monitor/2</span> is extended (e.g. to
handle other item types than <span class="code">process</span>), other
possible values for <span class="code">Object</span>, and <span class="code">Info</span> in the
<span class="code">'DOWN'</span> message will be introduced.</p>
</p></div>
</div>
<p>The monitoring is turned off either when the <span class="code">'DOWN'</span>
message is sent, or when
<span class="bold_code"><a href="#demonitor-1">demonitor/1</a></span>
is called.</p>
<p>If an attempt is made to monitor a process on an older node
(where remote process monitoring is not implemented or one
where remote process monitoring by registered name is not
implemented), the call fails with <span class="code">badarg</span>.</p>
<p>Making several calls to <span class="code">monitor/2</span> for the same
<span class="code">Item</span> is not an error; it results in as many, completely
independent, monitorings.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The format of the <span class="code">'DOWN'</span> message changed in the 5.2
version of the emulator (OTP release R9B) for monitor <strong>by registered name</strong>. The <span class="code">Object</span> element of
the <span class="code">'DOWN'</span> message could in earlier versions
sometimes be the pid of the monitored process and sometimes
be the registered name. Now the <span class="code">Object</span> element is
always a tuple consisting of the registered name and
the node name. Processes on new nodes (emulator version 5.2
or greater) will always get <span class="code">'DOWN'</span> messages on
the new format even if they are monitoring processes on old
nodes. Processes on old nodes will always get <span class="code">'DOWN'</span>
messages on the old format.</p>
</p></div>
</div>
</p></div>
<p><a name="monitor_node-2"><span class="bold_code">monitor_node(Node, Flag) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Node = node()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Flag = boolean()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Monitors the status of the node <span class="code">Node</span>. If <span class="code">Flag</span>
is <span class="code">true</span>, monitoring is turned on; if <span class="code">Flag</span> is
<span class="code">false</span>, monitoring is turned off.</p>
<p>Making several calls to <span class="code">monitor_node(Node, true)</span> for
the same <span class="code">Node</span> is not an error; it results in as many,
completely independent, monitorings.</p>
<p>If <span class="code">Node</span> fails or does not exist, the message
<span class="code">{nodedown, Node}</span> is delivered to the process. If a
process has made two calls to <span class="code">monitor_node(Node, true)</span>
and <span class="code">Node</span> terminates, two <span class="code">nodedown</span> messages are
delivered to the process. If there is no connection to
<span class="code">Node</span>, there will be an attempt to create one. If this
fails, a <span class="code">nodedown</span> message is delivered.</p>
<p>Nodes connected through hidden connections can be monitored
as any other node.</p>
<p>Failure: <span class="code">badarg</span>if the local node is not alive.</p>
</p></div>
<p><a name="monitor_node-3"><span class="bold_code">erlang:monitor_node(Node, Flag, Options) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Node = node()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Flag = boolean()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Options = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = allow_passive_connect</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Behaves as <span class="code">monitor_node/2</span> except that it allows an
extra option to be given, namely <span class="code">allow_passive_connect</span>.
The option allows the BIF to wait the normal net connection
timeout for the <strong>monitored node</strong> to connect itself,
even if it cannot be actively connected from this node
(i.e. it is blocked). The state where this might be useful can
only be achieved by using the kernel option
<span class="code">dist_auto_connect once</span>. If that kernel option is not
used, the <span class="code">allow_passive_connect</span> option has no
effect.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The <span class="code">allow_passive_connect</span> option is used
internally and is seldom needed in applications where the
network topology and the kernel options in effect is known in
advance.</p>
</p></div>
</div>
<p>Failure: <span class="code">badarg</span> if the local node is not alive or the
option list is malformed.</p>
</p></div>
<p><a name="nif_error-1"><span class="bold_code">erlang:nif_error(Reason)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Works exactly like
<span class="bold_code"><a href="#error-1">erlang:error/1</a></span>,
but Dialyzer thinks that this BIF will return an arbitrary term.
When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
will not generate false warnings.</p>
</p></div>
<p><a name="nif_error-2"><span class="bold_code">erlang:nif_error(Reason, Args)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Args = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Works exactly like
<span class="bold_code"><a href="#error-2">erlang:error/2</a></span>,
but Dialyzer thinks that this BIF will return an arbitrary term.
When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
will not generate false warnings.</p>
</p></div>
<p><a name="node-0"><span class="bold_code">node() -> Node</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Node = node()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the name of the local node. If the node is not alive,
<span class="code">nonode@nohost</span> is returned instead.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="node-1"><span class="bold_code">node(Arg) -> Node</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Arg = pid() | port() | reference()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Node = node()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the node where <span class="code">Arg</span> is located. <span class="code">Arg</span> can
be a pid, a reference, or a port. If the local node is not
alive, <span class="code">nonode@nohost</span> is returned.</p>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="nodes-0"></a><span class="bold_code">nodes() -> Nodes</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Nodes = [node()]</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns a list of all visible nodes in the system, excluding
the local node. Same as <span class="code">nodes(visible)</span>.</p>
</p></div>
<p><a name="nodes-1"><span class="bold_code">nodes(Arg | [Arg]) -> Nodes</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Arg = visible | hidden | connected | this | known</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Nodes = [node()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of nodes according to argument given.
The result returned when the argument is a list, is the list
of nodes satisfying the disjunction(s) of the list elements.</p>
<p><span class="code">Arg</span> can be any of the following:</p>
<dl>
<dt><strong><span class="code">visible</span></strong></dt>
<dd>
<p>Nodes connected to this node through normal connections.</p>
</dd>
<dt><strong><span class="code">hidden</span></strong></dt>
<dd>
<p>Nodes connected to this node through hidden connections.</p>
</dd>
<dt><strong><span class="code">connected</span></strong></dt>
<dd>
<p>All nodes connected to this node.</p>
</dd>
<dt><strong><span class="code">this</span></strong></dt>
<dd>
<p>This node.</p>
</dd>
<dt><strong><span class="code">known</span></strong></dt>
<dd>
<p>Nodes which are known to this node, i.e., connected,
previously connected, etc.</p>
</dd>
</dl>
<p>Some equalities: <span class="code">[node()] = nodes(this)</span>,
<span class="code">nodes(connected) = nodes([visible, hidden])</span>, and
<span class="code">nodes() = nodes(visible)</span>.</p>
<p>If the local node is not alive,
<span class="code">nodes(this) == nodes(known) == [nonode@nohost]</span>, for
any other <span class="code">Arg</span> the empty list [] is returned.</p>
</p></div>
<p><a name="now-0"><span class="bold_code">now() -> timestamp()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">timestamp() = {MegaSecs, Secs, MicroSecs}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">MegaSecs = Secs = MicroSecs = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the tuple <span class="code">{MegaSecs, Secs, MicroSecs}</span> which is
the elapsed time since 00:00 GMT, January 1, 1970 (zero hour)
on the assumption that the underlying OS supports this.
Otherwise, some other point in time is chosen. It is also
guaranteed that subsequent calls to this BIF returns
continuously increasing values. Hence, the return value from
<span class="code">now()</span> can be used to generate unique time-stamps,
and if it is called in a tight loop on a fast machine
the time of the node can become skewed.</p>
<p>It can only be used to check the local time of day if
the time-zone info of the underlying operating system is
properly configured.</p>
<p>If you do not need the return value to be unique and
monotonically increasing, use
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','os.html#timestamp-0');">os:timestamp/0</a></span>
instead to avoid some overhead.</p>
</p></div>
<p><a name="open_port-2"><span class="bold_code">open_port(PortName, PortSettings) -> port()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">PortName = {spawn, Command} | {spawn_driver, Command} | {spawn_executable, FileName} | {fd, In, Out}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Command = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> FileName = [ FileNameChar ] | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> FileNameChar = integer() (1..255 or any Unicode codepoint, see description)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> In = Out = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">PortSettings = [Opt]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Opt = {packet, N} | stream | {line, L} | {cd, Dir} | {env, Env} | {args, [ ArgString ]} | {arg0, ArgString} | exit_status | use_stdio | nouse_stdio | stderr_to_stdout | in | out | binary | eof</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> N = 1 | 2 | 4</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> L = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Dir = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> ArgString = [ FileNameChar ] | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Env = [{Name, Val}]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Name = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Val = string() | false</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a port identifier as the result of opening a
new Erlang port. A port can be seen as an external Erlang
process. <span class="code">PortName</span> is one of the following:</p>
<dl>
<dt><strong><span class="code">{spawn, Command}</span></strong></dt>
<dd>
<p>Starts an external program. <span class="code">Command</span> is the name
of the external program which will be run. <span class="code">Command</span>
runs outside the Erlang work space unless an Erlang
driver with the name <span class="code">Command</span> is found. If found,
that driver will be started. A driver runs in the Erlang
workspace, which means that it is linked with the Erlang
runtime system.</p>
<p>When starting external programs on Solaris, the system
call <span class="code">vfork</span> is used in preference to <span class="code">fork</span>
for performance reasons, although it has a history of
being less robust. If there are problems with using
<span class="code">vfork</span>, setting the environment variable
<span class="code">ERL_NO_VFORK</span> to any value will cause <span class="code">fork</span>
to be used instead.</p>
<p>For external programs, the <span class="code">PATH</span> is searched
(or an equivalent method is used to find programs,
depending on operating system). This is done by invoking
the shell on certain platforms. The first space
separated token of the command will be considered as the
name of the executable (or driver). This (among other
things) makes this option unsuitable for running
programs having spaces in file or directory names. Use
{spawn_executable, Command} instead if spaces in executable
file names is desired.</p>
</dd>
<dt><strong><span class="code">{spawn_driver, Command}</span></strong></dt>
<dd>
<p>Works like <span class="code">{spawn, Command}</span>, but demands the
first (space separated) token of the command to be the name of a
loaded driver. If no driver with that name is loaded, a
<span class="code">badarg</span> error is raised.</p>
</dd>
<dt><strong><span class="code">{spawn_executable, Command}</span></strong></dt>
<dd>
<p>Works like <span class="code">{spawn, Command}</span>, but only runs
external executables. The <span class="code">Command</span> in its whole
is used as the name of the executable, including any
spaces. If arguments are to be passed, the
<span class="code">args</span> and <span class="code">arg0</span> <span class="code">PortSettings</span> can be used.</p>
<p>The shell is not usually invoked to start the
program, it's executed directly. Neither is the
<span class="code">PATH</span> (or equivalent) searched. To find a program
in the PATH to execute, use <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','os.html#find_executable-1');">os:find_executable/1</a></span>.</p>
<p>Only if a shell script or <span class="code">.bat</span> file is
executed, the appropriate command interpreter will
implicitly be invoked, but there will still be no
command argument expansion or implicit PATH search.</p>
<p>The name of the executable as well as the arguments
given in <span class="code">args</span> and <span class="code">arg0</span> is subject to
Unicode file name translation if the system is running
in Unicode file name mode. To avoid
translation or force i.e. UTF-8, supply the executable
and/or arguments as a binary in the correct
encoding. See the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','file.html');">file</a></span> module, the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','file.html#native_name_encoding-0');">
file:native_name_encoding/0</a></span> function and the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','unicode_usage.html');">stdlib users guide
</a></span> for details.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p>The characters in the name (if given as a list)
can only be > 255 if the Erlang VM is started in
Unicode file name translation mode, otherwise the name
of the executable is limited to the ISO-latin-1
character set.</p></p></div>
</div>
<p>If the <span class="code">Command</span> cannot be run, an error
exception, with the posix error code as the reason, is
raised. The error reason may differ between operating
systems. Typically the error <span class="code">enoent</span> is raised
when one tries to run a program that is not found and
<span class="code">eaccess</span> is raised when the given file is not
executable.</p>
</dd>
<dt><strong><span class="code">{fd, In, Out}</span></strong></dt>
<dd>
<p>Allows an Erlang process to access any currently opened
file descriptors used by Erlang. The file descriptor
<span class="code">In</span> can be used for standard input, and the file
descriptor <span class="code">Out</span> for standard output. It is only
used for various servers in the Erlang operating system
(<span class="code">shell</span> and <span class="code">user</span>). Hence, its use is very
limited.</p>
</dd>
</dl>
<p><span class="code">PortSettings</span> is a list of settings for the port.
Valid settings are:</p>
<dl>
<dt><strong><span class="code">{packet, N}</span></strong></dt>
<dd>
<p>Messages are preceded by their length, sent in <span class="code">N</span>
bytes, with the most significant byte first. Valid values
for <span class="code">N</span> are 1, 2, or 4.</p>
</dd>
<dt><strong><span class="code">stream</span></strong></dt>
<dd>
<p>Output messages are sent without packet lengths. A
user-defined protocol must be used between the Erlang
process and the external object.</p>
</dd>
<dt><strong><span class="code">{line, L}</span></strong></dt>
<dd>
<p>Messages are delivered on a per line basis. Each line
(delimited by the OS-dependent newline sequence) is
delivered in one single message. The message data format
is <span class="code">{Flag, Line}</span>, where <span class="code">Flag</span> is either
<span class="code">eol</span> or <span class="code">noeol</span> and <span class="code">Line</span> is the actual
data delivered (without the newline sequence).</p>
<p><span class="code">L</span> specifies the maximum line length in bytes.
Lines longer than this will be delivered in more than one
message, with the <span class="code">Flag</span> set to <span class="code">noeol</span> for all
but the last message. If end of file is encountered
anywhere else than immediately following a newline
sequence, the last line will also be delivered with
the <span class="code">Flag</span> set to <span class="code">noeol</span>. In all other cases,
lines are delivered with <span class="code">Flag</span> set to <span class="code">eol</span>.</p>
<p>The <span class="code">{packet, N}</span> and <span class="code">{line, L}</span> settings are
mutually exclusive.</p>
</dd>
<dt><strong><span class="code">{cd, Dir}</span></strong></dt>
<dd>
<p>This is only valid for <span class="code">{spawn, Command}</span> and
<span class="code">{spawn_executable, Command}</span>.
The external program starts using <span class="code">Dir</span> as its
working directory. <span class="code">Dir</span> must be a string. Not
available on VxWorks.</p>
</dd>
<dt><strong><span class="code">{env, Env}</span></strong></dt>
<dd>
<p>This is only valid for <span class="code">{spawn, Command}</span> and
<span class="code">{spawn_executable, Command}</span>.
The environment of the started process is extended using
the environment specifications in <span class="code">Env</span>.</p>
<p><span class="code">Env</span> should be a list of tuples <span class="code">{Name, Val}</span>,
where <span class="code">Name</span> is the name of an environment variable,
and <span class="code">Val</span> is the value it is to have in the spawned
port process. Both <span class="code">Name</span> and <span class="code">Val</span> must be
strings. The one exception is <span class="code">Val</span> being the atom
<span class="code">false</span> (in analogy with <span class="code">os:getenv/1</span>), which
removes the environment variable.</p>
<p>If Unicode filename encoding is in effect (see the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#file_name_encoding');">erl manual
page</a></span>), the strings (both <span class="code">Name</span> and
<span class="code">Value</span>) may contain characters with codepoints > 255.</p>
</dd>
<dt><strong><span class="code">{args, [ string() ]}</span></strong></dt>
<dd>
<p>This option is only valid for <span class="code">{spawn_executable, Command}</span>
and specifies arguments to the executable. Each argument
is given as a separate string and (on Unix) eventually
ends up as one element each in the argument vector. On
other platforms, similar behavior is mimicked.</p>
<p>The arguments are not expanded by the shell prior to
being supplied to the executable, most notably this
means that file wildcard expansion will not happen. Use
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','filelib.html#wildcard-1');">filelib:wildcard/1</a></span>
to expand wildcards for the arguments. Note that even if
the program is a Unix shell script, meaning that the
shell will ultimately be invoked, wildcard expansion
will not happen and the script will be provided with the
untouched arguments. On Windows®, wildcard expansion
is always up to the program itself, why this isn't an
issue.</p>
<p>Note also that the actual executable name (a.k.a. <span class="code">argv[0]</span>)
should not be given in this list. The proper executable name will
automatically be used as argv[0] where applicable.</p>
<p>When the Erlang VM is running in Unicode file name
mode, the arguments can contain any Unicode characters and
will be translated into whatever is appropriate on the
underlying OS, which means UTF-8 for all platforms except
Windows, which has other (more transparent) ways of
dealing with Unicode arguments to programs. To avoid
Unicode translation of arguments, they can be supplied as
binaries in whatever encoding is deemed appropriate.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p>The characters in the arguments (if given as a
list of characters) can only be > 255 if the Erlang
VM is started in Unicode file name mode,
otherwise the arguments are limited to the
ISO-latin-1 character set.</p></p></div>
</div>
<p>If one, for any reason, wants to explicitly set the
program name in the argument vector, the <span class="code">arg0</span>
option can be used.</p>
</dd>
<dt><strong><span class="code">{arg0, string()}</span></strong></dt>
<dd>
<p>This option is only valid for <span class="code">{spawn_executable, Command}</span>
and explicitly specifies the program name argument when
running an executable. This might in some circumstances,
on some operating systems, be desirable. How the program
responds to this is highly system dependent and no specific
effect is guaranteed.</p>
<p>The unicode file name translation rules of the
<span class="code">args</span> option apply to this option as well.</p>
</dd>
<dt><strong><span class="code">exit_status</span></strong></dt>
<dd>
<p>This is only valid for <span class="code">{spawn, Command}</span> where
<span class="code">Command</span> refers to an external program, and for
<span class="code">{spawn_executable, Command}</span>.</p>
<p>When the external process connected to the port exits, a
message of the form <span class="code">{Port,{exit_status,Status}}</span> is
sent to the connected process, where <span class="code">Status</span> is the
exit status of the external process. If the program
aborts, on Unix the same convention is used as the shells
do (i.e., 128+signal).</p>
<p>If the <span class="code">eof</span> option has been given as well,
the <span class="code">eof</span> message and the <span class="code">exit_status</span> message
appear in an unspecified order.</p>
<p>If the port program closes its stdout without exiting,
the <span class="code">exit_status</span> option will not work.</p>
</dd>
<dt><strong><span class="code">use_stdio</span></strong></dt>
<dd>
<p>This is only valid for <span class="code">{spawn, Command}</span> and
<span class="code">{spawn_executable, Command}</span>. It
allows the standard input and output (file descriptors 0
and 1) of the spawned (UNIX) process for communication
with Erlang.</p>
</dd>
<dt><strong><span class="code">nouse_stdio</span></strong></dt>
<dd>
<p>The opposite of <span class="code">use_stdio</span>. Uses file descriptors
3 and 4 for communication with Erlang.</p>
</dd>
<dt><strong><span class="code">stderr_to_stdout</span></strong></dt>
<dd>
<p>Affects ports to external programs. The executed program
gets its standard error file redirected to its standard
output file. <span class="code">stderr_to_stdout</span> and
<span class="code">nouse_stdio</span> are mutually exclusive.</p>
</dd>
<dt><strong><span class="code">overlapped_io</span></strong></dt>
<dd>
<p>Affects ports to external programs on Windows® only.
The standard input and standard output handles of the port program
will, if this option is supplied, be opened with the flag
FILE_FLAG_OVERLAPPED, so that the port program can (and has to) do
overlapped I/O on its standard handles. This is not normally
the case for simple port programs, but an option of value for the
experienced Windows programmer. <strong>On all other platforms, this
option is silently discarded</strong>.</p>
</dd>
<dt><strong><span class="code">in</span></strong></dt>
<dd>
<p>The port can only be used for input.</p>
</dd>
<dt><strong><span class="code">out</span></strong></dt>
<dd>
<p>The port can only be used for output.</p>
</dd>
<dt><strong><span class="code">binary</span></strong></dt>
<dd>
<p>All IO from the port are binary data objects as opposed
to lists of bytes.</p>
</dd>
<dt><strong><span class="code">eof</span></strong></dt>
<dd>
<p>The port will not be closed at the end of the file and
produce an exit signal. Instead, it will remain open and
a <span class="code">{Port, eof}</span> message will be sent to the process
holding the port.</p>
</dd>
<dt><strong><span class="code">hide</span></strong></dt>
<dd>
<p>When running on Windows, suppress creation of a new
console window when spawning the port program.
(This option has no effect on other platforms.)</p>
</dd>
</dl>
<p>The default is <span class="code">stream</span> for all types of port and
<span class="code">use_stdio</span> for spawned ports.</p>
<p>Failure: If the port cannot be opened, the exit reason is
<span class="code">badarg</span>, <span class="code">system_limit</span>, or the Posix error code which
most closely describes the error, or <span class="code">einval</span> if no Posix code
is appropriate:</p>
<dl>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
<p>Bad input arguments to <span class="code">open_port</span>.</p>
</dd>
<dt><strong><span class="code">system_limit</span></strong></dt>
<dd>
<p>All available ports in the Erlang emulator are in use.</p>
</dd>
<dt><strong><span class="code">enomem</span></strong></dt>
<dd>
<p>There was not enough memory to create the port.</p>
</dd>
<dt><strong><span class="code">eagain</span></strong></dt>
<dd>
<p>There are no more available operating system processes.</p>
</dd>
<dt><strong><span class="code">enametoolong</span></strong></dt>
<dd>
<p>The external command given was too long.</p>
</dd>
<dt><strong><span class="code">emfile</span></strong></dt>
<dd>
<p>There are no more available file descriptors (for the operating system process
that the Erlang emulator runs in).</p>
</dd>
<dt><strong><span class="code">enfile</span></strong></dt>
<dd>
<p>The file table is full (for the entire operating system).</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>The <span class="code">Command</span> given in <span class="code">{spawn_executable, Command}</span> does not point out an executable file.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The <span class="code">Command</span> given in <span class="code">{spawn_executable, Command}</span> does not point out an existing file.</p>
</dd>
</dl>
<p>During use of a port opened using <span class="code">{spawn, Name}</span>,
<span class="code">{spawn_driver, Name}</span> or <span class="code">{spawn_executable, Name}</span>,
errors arising when sending messages to it are reported to
the owning process using signals of the form
<span class="code">{'EXIT', Port, PosixCode}</span>. See <span class="code">file(3)</span> for
possible values of <span class="code">PosixCode</span>.</p>
<p><a name="ERL_MAX_PORTS"></a>
The maximum number of ports that can be open at the same
time is 1024 by default, but can be configured by
the environment variable <span class="code">ERL_MAX_PORTS</span>.</p>
</p></div>
<p><a name="phash-2"><span class="bold_code">erlang:phash(Term, Range) -> Hash</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Range = 1..2^32</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Hash = 1..Range</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Portable hash function that will give the same hash for
the same Erlang term regardless of machine architecture and
ERTS version (the BIF was introduced in ERTS 4.9.1.1). Range
can be between 1 and 2^32, the function returns a hash value
for <span class="code">Term</span> within the range <span class="code">1..Range</span>.</p>
<p>This BIF could be used instead of the old deprecated
<span class="code">erlang:hash/2</span> BIF, as it calculates better hashes for
all data-types, but consider using <span class="code">phash2/1,2</span> instead.</p>
</p></div>
<p><a name="phash2-1"><span class="bold_code">erlang:phash2(Term [, Range]) -> Hash</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Range = 1..2^32</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Hash = 0..Range-1</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Portable hash function that will give the same hash for
the same Erlang term regardless of machine architecture and
ERTS version (the BIF was introduced in ERTS 5.2). Range can
be between 1 and 2^32, the function returns a hash value for
<span class="code">Term</span> within the range <span class="code">0..Range-1</span>. When called
without the <span class="code">Range</span> argument, a value in the range
<span class="code">0..2^27-1</span> is returned.</p>
<p>This BIF should always be used for hashing terms. It
distributes small integers better than <span class="code">phash/2</span>, and
it is faster for bignums and binaries.</p>
<p>Note that the range <span class="code">0..Range-1</span> is different from
the range of <span class="code">phash/2</span> (<span class="code">1..Range</span>).</p>
</p></div>
<p><a name="pid_to_list-1"><span class="bold_code">pid_to_list(Pid) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Pid</span>.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.</p>
</p></div>
</div>
</p></div>
<p><a name="port_close-1"><span class="bold_code">port_close(Port) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Closes an open port. Roughly the same as
<span class="code">Port ! {self(), close}</span> except for the error behaviour
(see below), and that the port does <strong>not</strong> reply with
<span class="code">{Port, closed}</span>. Any process may close a port with
<span class="code">port_close/1</span>, not only the port owner (the connected
process).</p>
<p>For comparison: <span class="code">Port ! {self(), close}</span> fails with
<span class="code">badarg</span> if <span class="code">Port</span> cannot be sent to (i.e.,
<span class="code">Port</span> refers neither to a port nor to a process). If
<span class="code">Port</span> is a closed port nothing happens. If <span class="code">Port</span>
is an open port and the calling process is the port owner,
the port replies with <span class="code">{Port, closed}</span> when all buffers
have been flushed and the port really closes, but if
the calling process is not the port owner the <strong>port owner</strong> fails with <span class="code">badsig</span>.</p>
<p>Note that any process can close a port using
<span class="code">Port ! {PortOwner, close}</span> just as if it itself was
the port owner, but the reply always goes to the port owner.</p>
<p>In short: <span class="code">port_close(Port)</span> has a cleaner and more
logical behaviour than <span class="code">Port ! {self(), close}</span>.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Port</span> is not an open port or
the registered name of an open port.</p>
</p></div>
<p><a name="port_command-2"><span class="bold_code">port_command(Port, Data) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sends data to a port. Same as
<span class="code">Port ! {self(), {command, Data}}</span> except for the error
behaviour (see below). Any process may send data to a port
with <span class="code">port_command/2</span>, not only the port owner
(the connected process).</p>
<p>For comparison: <span class="code">Port ! {self(), {command, Data}}</span>
fails with <span class="code">badarg</span> if <span class="code">Port</span> cannot be sent to
(i.e., <span class="code">Port</span> refers neither to a port nor to a process).
If <span class="code">Port</span> is a closed port the data message disappears
without a sound. If <span class="code">Port</span> is open and the calling
process is not the port owner, the <strong>port owner</strong> fails
with <span class="code">badsig</span>. The port owner fails with <span class="code">badsig</span>
also if <span class="code">Data</span> is not a valid IO list.</p>
<p>Note that any process can send to a port using
<span class="code">Port ! {PortOwner, {command, Data}}</span> just as if it
itself was the port owner.</p>
<p>In short: <span class="code">port_command(Port, Data)</span> has a cleaner and
more logical behaviour than
<span class="code">Port ! {self(), {command, Data}}</span>.</p>
<p>If the port is busy, the calling process will be suspended
until the port is not busy anymore.</p>
<p>Failures:</p>
<dl>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Port</span> is not an open port or the registered name
of an open port.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Data</span> is not a valid io list.
</dd>
</dl>
</p></div>
<p><a name="port_command-3"><span class="bold_code">port_command(Port, Data, OptionList) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">OptionList = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = force</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = nosuspend</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sends data to a port. <span class="code">port_command(Port, Data, [])</span>
equals <span class="code">port_command(Port, Data)</span>.</p>
<p>If the port command is aborted <span class="code">false</span> is returned;
otherwise, <span class="code">true</span> is returned.</p>
<p>If the port is busy, the calling process will be suspended
until the port is not busy anymore.</p>
<p>Currently the following <span class="code">Option</span>s are valid:</p>
<dl>
<dt><strong><span class="code">force</span></strong></dt>
<dd>The calling process will not be suspended if the port is
busy; instead, the port command is forced through. The
call will fail with a <span class="code">notsup</span> exception if the
driver of the port does not support this. For more
information see the
<span class="bold_code"><a href="driver_entry.html#driver_flags">ERL_DRV_FLAG_SOFT_BUSY</a></span>
driver flag.
</dd>
<dt><strong><span class="code">nosuspend</span></strong></dt>
<dd>The calling process will not be suspended if the port is
busy; instead, the port command is aborted and
<span class="code">false</span> is returned.
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>More options may be added in the future.</p>
</p></div>
</div>
<p>Failures:</p>
<dl>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Port</span> is not an open port or the registered name
of an open port.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Data</span> is not a valid io list.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">OptionList</span> is not a valid option list.
</dd>
<dt><strong><span class="code">notsup</span></strong></dt>
<dd>
If the <span class="code">force</span> option has been passed, but the
driver of the port does not allow forcing through
a busy port.
</dd>
</dl>
</p></div>
<p><a name="port_connect-2"><span class="bold_code">port_connect(Port, Pid) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets the port owner (the connected port) to <span class="code">Pid</span>.
Roughly the same as <span class="code">Port ! {self(), {connect, Pid}}</span>
except for the following:</p>
<ul>
<li>
<p>The error behavior differs, see below.</p>
</li>
<li>
<p>The port does <strong>not</strong> reply with
<span class="code">{Port,connected}</span>.</p>
</li>
<li>
<p>The new port owner gets linked to the port.</p>
</li>
</ul>
<p>The old port owner stays linked to the port and have to call
<span class="code">unlink(Port)</span> if this is not desired. Any process may
set the port owner to be any process with
<span class="code">port_connect/2</span>.</p>
<p>For comparison: <span class="code">Port ! {self(), {connect, Pid}}</span> fails
with <span class="code">badarg</span> if <span class="code">Port</span> cannot be sent to (i.e.,
<span class="code">Port</span> refers neither to a port nor to a process). If
<span class="code">Port</span> is a closed port nothing happens. If <span class="code">Port</span>
is an open port and the calling process is the port owner,
the port replies with <span class="code">{Port, connected}</span> to the old
port owner. Note that the old port owner is still linked to
the port, and that the new is not. If <span class="code">Port</span> is an open
port and the calling process is not the port owner,
the <strong>port owner</strong> fails with <span class="code">badsig</span>. The port
owner fails with <span class="code">badsig</span> also if <span class="code">Pid</span> is not an
existing local pid.</p>
<p>Note that any process can set the port owner using
<span class="code">Port ! {PortOwner, {connect, Pid}}</span> just as if it
itself was the port owner, but the reply always goes to
the port owner.</p>
<p>In short: <span class="code">port_connect(Port, Pid)</span> has a cleaner and
more logical behaviour than
<span class="code">Port ! {self(),{connect,Pid}}</span>.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Port</span> is not an open port
or the registered name of an open port, or if <span class="code">Pid</span> is
not an existing local pid.</p>
</p></div>
<p><a name="port_control-3"><span class="bold_code">port_control(Port, Operation, Data) -> Res</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Operation = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = Res = iodata()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Performs a synchronous control operation on a port.
The meaning of <span class="code">Operation</span> and <span class="code">Data</span> depends on
the port, i.e., on the port driver. Not all port drivers
support this control feature.</p>
<p>Returns: a list of integers in the range 0 through 255, or a
binary, depending on the port driver. The meaning of
the returned data also depends on the port driver.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Port</span> is not an open port or
the registered name of an open port, if <span class="code">Operation</span>
cannot fit in a 32-bit integer, if the port driver does not
support synchronous control operations, or if the port driver
so decides for any reason (probably something wrong with
<span class="code">Operation</span> or <span class="code">Data</span>).</p>
</p></div>
<p><a name="port_call-3"><span class="bold_code">erlang:port_call(Port, Operation, Data) -> term()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Operation = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Performs a synchronous call to a port. The meaning of
<span class="code">Operation</span> and <span class="code">Data</span> depends on the port, i.e.,
on the port driver. Not all port drivers support this feature.</p>
<p><span class="code">Port</span> is a port identifier, referring to a driver.</p>
<p><span class="code">Operation</span> is an integer, which is passed on to
the driver.</p>
<p><span class="code">Data</span> is any Erlang term. This data is converted to
binary term format and sent to the port.</p>
<p>Returns: a term from the driver. The meaning of the returned
data also depends on the port driver.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Port</span> is not an open port or
the registered name of an open port, if <span class="code">Operation</span>
cannot fit in a 32-bit integer, if the port driver does not
support synchronous control operations, or if the port driver
so decides for any reason (probably something wrong with
<span class="code">Operation</span> or <span class="code">Data</span>).</p>
</p></div>
<p><a name="port_info-1"><span class="bold_code">erlang:port_info(Port) -> [{Item, Info}] | undefined</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item, Info -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list containing tuples with information about
the <span class="code">Port</span>, or <span class="code">undefined</span> if the port is not open.
The order of the tuples is not defined, nor are all the
tuples mandatory.</p>
<dl>
<dt><strong><span class="code">{registered_name, RegName}</span></strong></dt>
<dd>
<p><span class="code">RegName</span> (an atom) is the registered name of
the port. If the port has no registered name, this tuple
is not present in the list.</p>
</dd>
<dt><strong><span class="code">{id, Index}</span></strong></dt>
<dd>
<p><span class="code">Index</span> (an integer) is the internal index of the
port. This index may be used to separate ports.</p>
</dd>
<dt><strong><span class="code">{connected, Pid}</span></strong></dt>
<dd>
<p><span class="code">Pid</span> is the process connected to the port.</p>
</dd>
<dt><strong><span class="code">{links, Pids}</span></strong></dt>
<dd>
<p><span class="code">Pids</span> is a list of pids to which processes the
port is linked.</p>
</dd>
<dt><strong><span class="code">{name, String}</span></strong></dt>
<dd>
<p><span class="code">String</span> is the command name set by
<span class="code">open_port</span>.</p>
</dd>
<dt><strong><span class="code">{input, Bytes}</span></strong></dt>
<dd>
<p><span class="code">Bytes</span> is the total number of bytes read from
the port.</p>
</dd>
<dt><strong><span class="code">{output, Bytes}</span></strong></dt>
<dd>
<p><span class="code">Bytes</span> is the total number of bytes written to
the port.</p>
</dd>
<dt><strong><span class="code">{os_pid, Integer | undefined}</span></strong></dt>
<dd>
<p><span class="code">Integer</span> is the process identifier (or equivalent) of an OS process created with <span class="code">open_port({spawn | spawn_executable, Command}, Options)</span>. If the port is not the result of spawning an OS process, the value is <span class="code">undefined</span>.</p>
</dd>
</dl>
<p>Failure: <span class="code">badarg</span> if <span class="code">Port</span> is not a local port.</p>
</p></div>
<p><a name="port_info-2"><span class="bold_code">erlang:port_info(Port, Item) -> {Item, Info} | undefined | []</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port() | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item, Info -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns information about <span class="code">Port</span> as specified
by <span class="code">Item</span>, or <span class="code">undefined</span> if the port is not open.
Also, if <span class="code">Item == registered_name</span> and the port has no
registered name, [] is returned.</p>
<p>For valid values of <span class="code">Item</span>, and corresponding
values of <span class="code">Info</span>, see
<span class="bold_code"><a href="#port_info-1">erlang:port_info/1</a></span>.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Port</span> is not a local port.</p>
</p></div>
<p><a name="port_to_list-1"><span class="bold_code">erlang:port_to_list(Port) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Port = port()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of the port identifier <span class="code">Port</span>.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.</p>
</p></div>
</div>
</p></div>
<p><a name="ports-0"><span class="bold_code">erlang:ports() -> [port()]</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns a list of all ports on the local node.</p>
</p></div>
<p><a name="pre_loaded-0"><span class="bold_code">pre_loaded() -> [Module]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of Erlang modules which are pre-loaded in
the system. As all loading of code is done through the file
system, the file system must have been loaded previously.
Hence, at least the module <span class="code">init</span> must be pre-loaded.</p>
</p></div>
<p><a name="process_display-2"><span class="bold_code">erlang:process_display(Pid, Type) -> void()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Type = backtrace</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Writes information about the local process <span class="code">Pid</span> on
standard error. The currently allowed value for the atom
<span class="code">Type</span> is <span class="code">backtrace</span>, which shows the contents of
the call stack, including information about the call chain, with
the current function printed first. The format of the output
is not further defined.</p>
</p></div>
<p><a name="process_flag-2"><span class="bold_code">process_flag(Flag, Value) -> OldValue</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Flag, Value, OldValue -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets certain flags for the process which calls this
function. Returns the old value of the flag.</p>
<dl>
<dt><strong><span class="code">process_flag(trap_exit, Boolean)</span></strong></dt>
<dd>
<p>When <span class="code">trap_exit</span> is set to <span class="code">true</span>, exit signals
arriving to a process are converted to <span class="code">{'EXIT', From, Reason}</span> messages, which can be received as ordinary
messages. If <span class="code">trap_exit</span> is set to <span class="code">false</span>, the
process exits if it receives an exit signal other than
<span class="code">normal</span> and the exit signal is propagated to its
linked processes. Application processes should normally
not trap exits.</p>
<p>See also <span class="bold_code"><a href="#exit-2">exit/2</a></span>.</p>
</dd>
<dt><strong><span class="code">process_flag(error_handler, Module)</span></strong></dt>
<dd>
<p>This is used by a process to redefine the error handler
for undefined function calls and undefined registered
processes. Inexperienced users should not use this flag
since code auto-loading is dependent on the correct
operation of the error handling module.</p>
</dd>
<dt><strong><span class="code">process_flag(min_heap_size, MinHeapSize)</span></strong></dt>
<dd>
<p>This changes the minimum heap size for the calling
process.</p>
</dd>
<dt><strong><span class="code">process_flag(min_bin_vheap_size, MinBinVHeapSize)</span></strong></dt>
<dd>
<p>This changes the minimum binary virtual heap size for the calling
process.</p>
</dd>
<dt><strong><a name="process_flag_priority"><span class="code">process_flag(priority, Level)</span></a></strong></dt>
<dd>
<p>This sets the process priority. <span class="code">Level</span> is an atom.
There are currently four priority levels: <span class="code">low</span>,
<span class="code">normal</span>, <span class="code">high</span>, and <span class="code">max</span>. The default
priority level is <span class="code">normal</span>. <strong>NOTE</strong>: The
<span class="code">max</span> priority level is reserved for internal use in
the Erlang runtime system, and should <strong>not</strong> be used
by others.
</p>
<p>Internally in each priority level processes are scheduled
in a round robin fashion.
</p>
<p>Execution of processes on priority <span class="code">normal</span> and
priority <span class="code">low</span> will be interleaved. Processes on
priority <span class="code">low</span> will be selected for execution less
frequently than processes on priority <span class="code">normal</span>.
</p>
<p>When there are runnable processes on priority <span class="code">high</span>
no processes on priority <span class="code">low</span>, or <span class="code">normal</span> will
be selected for execution. Note, however, that this does
<strong>not</strong> mean that no processes on priority <span class="code">low</span>,
or <span class="code">normal</span> will be able to run when there are
processes on priority <span class="code">high</span> running. On the runtime
system with SMP support there might be more processes running
in parallel than processes on priority <span class="code">high</span>, i.e.,
a <span class="code">low</span>, and a <span class="code">high</span> priority process might
execute at the same time.
</p>
<p>When there are runnable processes on priority <span class="code">max</span>
no processes on priority <span class="code">low</span>, <span class="code">normal</span>, or
<span class="code">high</span> will be selected for execution. As with the
<span class="code">high</span> priority, processes on lower priorities might
execute in parallel with processes on priority <span class="code">max</span>.
</p>
<p>Scheduling is preemptive. Regardless of priority, a process
is preempted when it has consumed more than a certain amount
of reductions since the last time it was selected for
execution.
</p>
<p><strong>NOTE</strong>: You should not depend on the scheduling
to remain exactly as it is today. Scheduling, at least on
the runtime system with SMP support, is very likely to be
modified in the future in order to better utilize available
processor cores.
</p>
<p>There is currently <strong>no</strong> automatic mechanism for
avoiding priority inversion, such as priority inheritance,
or priority ceilings. When using priorities you have
to take this into account and handle such scenarios by
yourself.
</p>
<p>Making calls from a <span class="code">high</span> priority process into code
that you don't have control over may cause the <span class="code">high</span>
priority process to wait for a processes with lower
priority, i.e., effectively decreasing the priority of the
<span class="code">high</span> priority process during the call. Even if this
isn't the case with one version of the code that you don't
have under your control, it might be the case in a future
version of it. This might, for example, happen if a
<span class="code">high</span> priority process triggers code loading, since
the code server runs on priority <span class="code">normal</span>.
</p>
<p>Other priorities than <span class="code">normal</span> are normally not needed.
When other priorities are used, they need to be used
with care, especially the <span class="code">high</span> priority <strong>must</strong>
be used with care. A process on <span class="code">high</span> priority should
only perform work for short periods of time. Busy looping for
long periods of time in a <span class="code">high</span> priority process will
most likely cause problems, since there are important servers
in OTP running on priority <span class="code">normal</span>.
</p>
</dd>
<dt><strong><span class="code">process_flag(save_calls, N)</span></strong></dt>
<dd>
<p><span class="code">N</span> must be an integer in the interval 0..10000.
If <span class="code">N</span> > 0, call saving is made active for the
process, which means that information about the <span class="code">N</span>
most recent global function calls, BIF calls, sends and
receives made by the process are saved in a list, which
can be retrieved with
<span class="code">process_info(Pid, last_calls)</span>. A global function
call is one in which the module of the function is
explicitly mentioned. Only a fixed amount of information
is saved: a tuple <span class="code">{Module, Function, Arity}</span> for
function calls, and the mere atoms <span class="code">send</span>,
<span class="code">'receive'</span> and <span class="code">timeout</span> for sends and receives
(<span class="code">'receive'</span> when a message is received and
<span class="code">timeout</span> when a receive times out). If <span class="code">N</span> = 0,
call saving is disabled for the process, which is the
default. Whenever the size of the call saving list is set,
its contents are reset.</p>
</dd>
<dt><strong><span class="code">process_flag(sensitive, Boolean)</span></strong></dt>
<dd>
<p>Set or clear the <span class="code">sensitive</span> flag for the current process.
When a process has been marked as sensitive by calling
<span class="code">process_flag(sensitive, true)</span>, features in the run-time
system that can be used for examining the data and/or inner working
of the process are silently disabled.</p>
<p>Features that are disabled include (but are not limited to)
the following:</p>
<p>Tracing: Trace flags can still be set for the process, but no
trace messages of any kind will be generated.
(If the <span class="code">sensitive</span> flag is turned off, trace messages will
again be generated if there are any trace flags set.)</p>
<p>Sequential tracing: The sequential trace token will be propagated
as usual, but no sequential trace messages will be generated.</p>
<p><span class="code">process_info/1,2</span> cannot be used to read out the message
queue or the process dictionary (both will be returned as empty lists).</p>
<p>Stack back-traces cannot be displayed for the process.</p>
<p>In crash dumps, the stack, messages, and the process dictionary
will be omitted.</p>
<p>If <span class="code">{save_calls,N}</span> has been set for the process, no
function calls will be saved to the call saving list.
(The call saving list will not be cleared; furthermore, send, receive,
and timeout events will still be added to the list.)</p>
</dd>
</dl>
</p></div>
<p><a name="process_flag-3"><span class="bold_code">process_flag(Pid, Flag, Value) -> OldValue</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Flag, Value, OldValue -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets certain flags for the process <span class="code">Pid</span>, in the same
manner as
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>.
Returns the old value of the flag. The allowed values for
<span class="code">Flag</span> are only a subset of those allowed in
<span class="code">process_flag/2</span>, namely: <span class="code">save_calls</span>.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Pid</span> is not a local process.</p>
</p></div>
<p><a name="process_info-1"><span class="bold_code">process_info(Pid) -> InfoResult</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Info = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InfoTuple = {Item, Info}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InfoTupleList = [InfoTuple]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InfoResult = InfoTupleList | undefined</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list containing <span class="code">InfoTuple</span>s with
miscellaneous information about the process identified by
<span class="code">Pid</span>, or <span class="code">undefined</span> if the process is not alive.
</p>
<p>
The order of the <span class="code">InfoTuple</span>s is not defined, nor
are all the <span class="code">InfoTuple</span>s mandatory. The <span class="code">InfoTuple</span>s
part of the result may be changed without prior notice.
Currently <span class="code">InfoTuple</span>s with the following <span class="code">Item</span>s
are part of the result:
<span class="code">current_function</span>, <span class="code">initial_call</span>, <span class="code">status</span>,
<span class="code">message_queue_len</span>, <span class="code">messages</span>, <span class="code">links</span>,
<span class="code">dictionary</span>, <span class="code">trap_exit</span>, <span class="code">error_handler</span>,
<span class="code">priority</span>, <span class="code">group_leader</span>, <span class="code">total_heap_size</span>,
<span class="code">heap_size</span>, <span class="code">stack_size</span>, <span class="code">reductions</span>, and
<span class="code">garbage_collection</span>.
If the process identified by <span class="code">Pid</span> has a registered name
also an <span class="code">InfoTuple</span> with <span class="code">Item == registered_name</span>
will appear.
</p>
<p>See <span class="bold_code"><a href="#process_info-2">process_info/2</a></span>
for information about specific <span class="code">InfoTuple</span>s.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for <strong>debugging only</strong>, use
<span class="bold_code"><a href="#process_info-2">process_info/2</a></span>
for all other purposes.
</p>
</p></div>
</div>
<p>Failure: <span class="code">badarg</span> if <span class="code">Pid</span> is not a local process.</p>
</p></div>
<p><a name="process_info-2"><span class="bold_code">process_info(Pid, ItemSpec) -> InfoResult</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Info = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">ItemList = [Item]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">ItemSpec = Item | ItemList</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InfoTuple = {Item, Info}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InfoTupleList = [InfoTuple]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">InfoResult = InfoTuple | InfoTupleList | undefined | []</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns information about the process identified by <span class="code">Pid</span>
as specified by the <span class="code">ItemSpec</span>, or <span class="code">undefined</span> if the
process is not alive.
</p>
<p>If the process is alive and <span class="code">ItemSpec</span> is a single
<span class="code">Item</span>, the returned value is the corresponding
<span class="code">InfoTuple</span> unless <span class="code">ItemSpec == registered_name</span>
and the process has no registered name. In this case
<span class="code">[]</span> is returned. This strange behavior is due to
historical reasons, and is kept for backward compatibility.
</p>
<p>If <span class="code">ItemSpec</span> is an <span class="code">ItemList</span>, the result is an
<span class="code">InfoTupleList</span>. The <span class="code">InfoTuple</span>s in the
<span class="code">InfoTupleList</span> will appear with the corresponding
<span class="code">Item</span>s in the same order as the <span class="code">Item</span>s appeared
in the <span class="code">ItemList</span>. Valid <span class="code">Item</span>s may appear multiple
times in the <span class="code">ItemList</span>.
</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p>If <span class="code">registered_name</span> is part of an <span class="code">ItemList</span>
and the process has no name registered a
<span class="code">{registered_name, []}</span> <span class="code">InfoTuple</span> <strong>will</strong>
appear in the resulting <span class="code">InfoTupleList</span>. This
behavior is different than when
<span class="code">ItemSpec == registered_name</span>, and than when
<span class="code">process_info/1</span> is used.
</p></p></div>
</div>
<p>Currently the following <span class="code">InfoTuple</span>s with corresponding
<span class="code">Item</span>s are valid:</p>
<dl>
<dt><strong><span class="code">{backtrace, Bin}</span></strong></dt>
<dd>
<p>The binary <span class="code">Bin</span> contains the same information as
the output from
<span class="code">erlang:process_display(Pid, backtrace)</span>. Use
<span class="code">binary_to_list/1</span> to obtain the string of characters
from the binary.</p>
</dd>
<dt><strong><span class="code">{binary, BinInfo}</span></strong></dt>
<dd>
<p><span class="code">BinInfo</span> is a list containing miscellaneous information
about binaries currently being referred to by this process.
This <span class="code">InfoTuple</span> may be changed or removed without prior
notice.</p>
</dd>
<dt><strong><span class="code">{catchlevel, CatchLevel}</span></strong></dt>
<dd>
<p><span class="code">CatchLevel</span> is the number of currently active
catches in this process. This <span class="code">InfoTuple</span> may be
changed or removed without prior notice.</p>
</dd>
<dt><strong><span class="code">{current_function, {Module, Function, Arity}}</span></strong></dt>
<dd>
<p><span class="code">Module</span>, <span class="code">Function</span>, <span class="code">Arity</span> is
the current function call of the process.</p>
</dd>
<dt><strong><span class="code">{current_location, {Module, Function, Arity, Location}}</span></strong></dt>
<dd>
<p><span class="code">Module</span>, <span class="code">Function</span>, <span class="code">Arity</span> is
the current function call of the process.
<span class="code">Location</span> is a list of two-tuples that describes the
location in the source code.
</p>
</dd>
<dt><strong><span class="code">{current_stacktrace, Stack}</span></strong></dt>
<dd>
<p>Return the current call stack back-trace (<strong>stacktrace</strong>)
of the process. The stack has the same format as returned by
<span class="bold_code"><a href="#get_stacktrace-0">erlang:get_stacktrace/0</a></span>.
</p>
</dd>
<dt><strong><span class="code">{dictionary, Dictionary}</span></strong></dt>
<dd>
<p><span class="code">Dictionary</span> is the dictionary of the process.</p>
</dd>
<dt><strong><span class="code">{error_handler, Module}</span></strong></dt>
<dd>
<p><span class="code">Module</span> is the error handler module used by
the process (for undefined function calls, for example).</p>
</dd>
<dt><strong><span class="code">{garbage_collection, GCInfo}</span></strong></dt>
<dd>
<p><span class="code">GCInfo</span> is a list which contains miscellaneous
information about garbage collection for this process.
The content of <span class="code">GCInfo</span> may be changed without
prior notice.</p>
</dd>
<dt><strong><span class="code">{group_leader, GroupLeader}</span></strong></dt>
<dd>
<p><span class="code">GroupLeader</span> is group leader for the IO of
the process.</p>
</dd>
<dt><strong><span class="code">{heap_size, Size}</span></strong></dt>
<dd>
<p><span class="code">Size</span> is the size in words of youngest heap generation
of the process. This generation currently include the stack
of the process. This information is highly implementation
dependent, and may change if the implementation change.
</p>
</dd>
<dt><strong><span class="code">{initial_call, {Module, Function, Arity}}</span></strong></dt>
<dd>
<p><span class="code">Module</span>, <span class="code">Function</span>, <span class="code">Arity</span> is
the initial function call with which the process was
spawned.</p>
</dd>
<dt><strong><span class="code">{links, PidsAndPorts}</span></strong></dt>
<dd>
<p><span class="code">PidsAndPorts</span> is a list of pids and port identifiers, with
processes or ports to which the process has a link.</p>
</dd>
<dt><strong><span class="code">{last_calls, false|Calls}</span></strong></dt>
<dd>
<p>The value is <span class="code">false</span> if call saving is not active
for the process (see
<span class="bold_code"><a href="#process_flag-3">process_flag/3</a></span>).
If call saving is active, a list is returned, in which
the last element is the most recent called.</p>
</dd>
<dt><strong><span class="code">{memory, Size}</span></strong></dt>
<dd>
<p><span class="code">Size</span> is the size in bytes of the process. This
includes call stack, heap and internal structures.</p>
</dd>
<dt><strong><span class="code">{message_queue_len, MessageQueueLen}</span></strong></dt>
<dd>
<p><span class="code">MessageQueueLen</span> is the number of messages
currently in the message queue of the process. This is
the length of the list <span class="code">MessageQueue</span> returned as
the info item <span class="code">messages</span> (see below).</p>
</dd>
<dt><strong><span class="code">{messages, MessageQueue}</span></strong></dt>
<dd>
<p><span class="code">MessageQueue</span> is a list of the messages to
the process, which have not yet been processed.</p>
</dd>
<dt><strong><span class="code">{min_heap_size, MinHeapSize}</span></strong></dt>
<dd>
<p><span class="code">MinHeapSize</span> is the minimum heap size for the process.</p>
</dd>
<dt><strong><span class="code">{min_bin_vheap_size, MinBinVHeapSize}</span></strong></dt>
<dd>
<p><span class="code">MinBinVHeapSize</span> is the minimum binary virtual heap size for the process.</p>
</dd>
<dt><strong><span class="code">{monitored_by, Pids}</span></strong></dt>
<dd>
<p>A list of pids that are monitoring the process (with
<span class="code">monitor/2</span>).</p>
</dd>
<dt><strong><span class="code">{monitors, Monitors}</span></strong></dt>
<dd>
<p>A list of monitors (started by <span class="code">monitor/2</span>)
that are active for the process. For a local process
monitor or a remote process monitor by pid, the list item
is <span class="code">{process, Pid}</span>, and for a remote process
monitor by name, the list item is
<span class="code">{process, {RegName, Node}}</span>.</p>
</dd>
<dt><strong><span class="code">{priority, Level}</span></strong></dt>
<dd>
<p><span class="code">Level</span> is the current priority level for
the process. For more information on priorities see
<span class="bold_code"><a href="#process_flag_priority">process_flag(priority, Level)</a></span>.</p>
</dd>
<dt><strong><span class="code">{reductions, Number}</span></strong></dt>
<dd>
<p><span class="code">Number</span> is the number of reductions executed by
the process.</p>
</dd>
<dt><strong><span class="code">{registered_name, Atom}</span></strong></dt>
<dd>
<p><span class="code">Atom</span> is the registered name of the process. If
the process has no registered name, this tuple is not
present in the list.</p>
</dd>
<dt><strong><span class="code">{sequential_trace_token, [] | SequentialTraceToken}</span></strong></dt>
<dd>
<p><span class="code">SequentialTraceToken</span> the sequential trace token for
the process. This <span class="code">InfoTuple</span> may be changed or removed
without prior notice.</p>
</dd>
<dt><strong><span class="code">{stack_size, Size}</span></strong></dt>
<dd>
<p><span class="code">Size</span> is the stack size of the process in words.</p>
</dd>
<dt><strong><span class="code">{status, Status}</span></strong></dt>
<dd>
<p><span class="code">Status</span> is the status of the process. <span class="code">Status</span>
is <span class="code">exiting</span>, <span class="code">garbage_collecting</span>,
<span class="code">waiting</span> (for a message), <span class="code">running</span>,
<span class="code">runnable</span> (ready to run, but another process is
running), or <span class="code">suspended</span> (suspended on a "busy" port
or by the <span class="code">erlang:suspend_process/[1,2]</span> BIF).</p>
</dd>
<dt><strong><span class="code">{suspending, SuspendeeList}</span></strong></dt>
<dd>
<p><span class="code">SuspendeeList</span> is a list of <span class="code">{Suspendee,
ActiveSuspendCount, OutstandingSuspendCount}</span> tuples.
<span class="code">Suspendee</span> is the pid of a process that have been or is to
be suspended by the process identified by <span class="code">Pid</span> via the
<span class="bold_code"><a href="#suspend_process-2">erlang:suspend_process/2</a></span>
BIF, or the
<span class="bold_code"><a href="#suspend_process-1">erlang:suspend_process/1</a></span>
BIF. <span class="code">ActiveSuspendCount</span> is the number of times the
<span class="code">Suspendee</span> has been suspended by <span class="code">Pid</span>.
<span class="code">OutstandingSuspendCount</span> is the number of not yet
completed suspend requests sent by <span class="code">Pid</span>. That is,
if <span class="code">ActiveSuspendCount /= 0</span>, <span class="code">Suspendee</span> is
currently in the suspended state, and if
<span class="code">OutstandingSuspendCount /= 0</span> the <span class="code">asynchronous</span>
option of <span class="code">erlang:suspend_process/2</span> has been used and
the suspendee has not yet been suspended by <span class="code">Pid</span>.
Note that the <span class="code">ActiveSuspendCount</span> and
<span class="code">OutstandingSuspendCount</span> are not the total suspend count
on <span class="code">Suspendee</span>, only the parts contributed by <span class="code">Pid</span>.
</p>
</dd>
<dt><strong><span class="code">{total_heap_size, Size}</span></strong></dt>
<dd>
<p><span class="code">Size</span> is the total size in words of all heap
fragments of the process. This currently include the stack
of the process.
</p>
</dd>
<dt><strong><span class="code">{trace, InternalTraceFlags}</span></strong></dt>
<dd>
<p><span class="code">InternalTraceFlags</span> is an integer representing
internal trace flag for this process. This <span class="code">InfoTuple</span>
may be changed or removed without prior notice.</p>
</dd>
<dt><strong><span class="code">{trap_exit, Boolean}</span></strong></dt>
<dd>
<p><span class="code">Boolean</span> is <span class="code">true</span> if the process is trapping
exits, otherwise it is <span class="code">false</span>.</p>
</dd>
</dl>
<p>Note however, that not all implementations support every one
of the above <span class="code">Items</span>.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Pid</span> is not a local process,
or if <span class="code">Item</span> is not a valid <span class="code">Item</span>.</p>
</p></div>
<p><a name="processes-0"><span class="bold_code">processes() -> [pid()]</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns a list of process identifiers corresponding to
all the processes currently existing on the local node.
</p>
<p>Note that a process that is exiting, exists but is not alive, i.e.,
<span class="code">is_process_alive/1</span> will return <span class="code">false</span> for a process
that is exiting, but its process identifier will be part
of the result returned from <span class="code">processes/0</span>.
</p>
<div class="example"><pre>
> <span class="bold_code">processes().</span>
[<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]</pre></div>
</p></div>
<p><a name="purge_module-1"><span class="bold_code">purge_module(Module) -> void()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Removes old code for <span class="code">Module</span>. Before this BIF is used,
<span class="code">erlang:check_process_code/2</span> should be called to check
that no processes are executing old code in the module.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for the code server (see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','kernel','code.html');">code(3)</a></span>) and should not be
used elsewhere.</p>
</p></div>
</div>
<p>Failure: <span class="code">badarg</span> if there is no old code for
<span class="code">Module</span>.</p>
</p></div>
<p><a name="put-2"><span class="bold_code">put(Key, Val) -> OldVal | undefined</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Key = Val = OldVal = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Adds a new <span class="code">Key</span> to the process dictionary, associated
with the value <span class="code">Val</span>, and returns <span class="code">undefined</span>. If
<span class="code">Key</span> already exists, the old value is deleted and
replaced by <span class="code">Val</span> and the function returns the old value.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The values stored when <span class="code">put</span> is evaluated within
the scope of a <span class="code">catch</span> will not be retracted if a
<span class="code">throw</span> is evaluated, or if an error occurs.</p>
</p></div>
</div>
<div class="example"><pre>
> <span class="bold_code">X = put(name, walrus), Y = put(name, carpenter),</span>
<span class="bold_code">Z = get(name),</span>
<span class="bold_code">{X, Y, Z}.</span>
{undefined,walrus,carpenter}</pre></div>
</p></div>
<p><a name="raise-3"><span class="bold_code">erlang:raise(Class, Reason, Stacktrace)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Class = error | exit | throw</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Stacktrace = [{Module, Function, Arity | Args} | {Fun, Args}]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Arity = arity()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Args = [term()]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Fun = [fun()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Stops the execution of the calling process with an
exception of given class, reason and call stack backtrace
(<strong>stacktrace</strong>).</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging and for use in
the Erlang operating system. In general, it should
be avoided in applications, unless you know
very well what you are doing.</p>
</p></div>
</div>
<p><span class="code">Class</span> is one of <span class="code">error</span>, <span class="code">exit</span> or
<span class="code">throw</span>, so if it were not for the stacktrace
<span class="code">erlang:raise(Class, Reason, Stacktrace)</span> is
equivalent to <span class="code">erlang:Class(Reason)</span>.
<span class="code">Reason</span> is any term and <span class="code">Stacktrace</span> is a list as
returned from <span class="code">get_stacktrace()</span>, that is a list of
4-tuples <span class="code">{Module, Function, Arity | Args,
Location}</span> where <span class="code">Module</span> and <span class="code">Function</span>
are atoms and the third element is an integer arity or an
argument list. The stacktrace may also contain <span class="code">{Fun,
Args, Location}</span> tuples where
<span class="code">Fun</span> is a local fun and <span class="code">Args</span> is an argument list.</p>
<p>The <span class="code">Location</span> element at the end is optional.
Omitting it is equivalent to specifying an empty list.</p>
<p>The stacktrace is used as the exception stacktrace for the
calling process; it will be truncated to the current
maximum stacktrace depth.</p>
<p>Because evaluating this function causes the process to
terminate, it has no return value - unless the arguments are
invalid, in which case the function <strong>returns the error reason</strong>, that is <span class="code">badarg</span>. If you want to be
really sure not to return you can call
<span class="code">error(erlang:raise(Class, Reason, Stacktrace))</span>
and hope to distinguish exceptions later.</p>
</p></div>
<p><a name="read_timer-1"><span class="bold_code">erlang:read_timer(TimerRef) -> integer() >= 0 | false</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">TimerRef = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">TimerRef</span> is a timer reference returned by
<span class="bold_code"><a href="#send_after-3">erlang:send_after/3</a></span>
or
<span class="bold_code"><a href="#start_timer-3">erlang:start_timer/3</a></span>.
If the timer is active, the function returns the time in
milliseconds left until the timer will expire, otherwise
<span class="code">false</span> (which means that <span class="code">TimerRef</span> was never a
timer, that it has been cancelled, or that it has already
delivered its message).</p>
<p>See also
<span class="bold_code"><a href="#send_after-3">erlang:send_after/3</a></span>,
<span class="bold_code"><a href="#start_timer-3">erlang:start_timer/3</a></span>,
and
<span class="bold_code"><a href="#cancel_timer-1">erlang:cancel_timer/1</a></span>.</p>
</p></div>
<p><a name="ref_to_list-1"><span class="bold_code">erlang:ref_to_list(Ref) -> string()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Ref = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a string which corresponds to the text
representation of <span class="code">Ref</span>.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.</p>
</p></div>
</div>
</p></div>
<p><a name="register-2"><span class="bold_code">register(RegName, Pid | Port) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">RegName = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Port = port()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Associates the name <span class="code">RegName</span> with a pid or a port
identifier. <span class="code">RegName</span>, which must be an atom, can be used
instead of the pid / port identifier in the send operator
(<span class="code">RegName ! Message</span>).</p>
<div class="example"><pre>
> <span class="bold_code">register(db, Pid).</span>
true</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">Pid</span> is not an existing,
local process or port, if <span class="code">RegName</span> is already in use,
if the process or port is already registered (already has a
name), or if <span class="code">RegName</span> is the atom <span class="code">undefined</span>.</p>
</p></div>
<p><a name="registered-0"><span class="bold_code">registered() -> [RegName]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">RegName = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list of names which have been registered using
<span class="bold_code"><a href="#register-2">register/2</a></span>.</p>
<div class="example"><pre>
> <span class="bold_code">registered().</span>
[code_server, file_server, init, user, my_db]</pre></div>
</p></div>
<p><a name="resume_process-1"><span class="bold_code">erlang:resume_process(Suspendee) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Suspendee = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Decreases the suspend count on the process identified by
<span class="code">Suspendee</span>. <span class="code">Suspendee</span> should previously have been
suspended via
<span class="bold_code"><a href="#suspend_process-2">erlang:suspend_process/2</a></span>,
or
<span class="bold_code"><a href="#suspend_process-1">erlang:suspend_process/1</a></span>
by the process calling <span class="code">erlang:resume_process(Suspendee)</span>. When
the suspend count on <span class="code">Suspendee</span> reach zero, <span class="code">Suspendee</span>
will be resumed, i.e., the state of the <span class="code">Suspendee</span> is changed
from suspended into the state <span class="code">Suspendee</span> was in before it was
suspended.
</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging only.</p>
</p></div>
</div>
<p>Failures:</p>
<dl>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Suspendee</span> isn't a process identifier.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If the process calling <span class="code">erlang:resume_process/1</span> had
not previously increased the suspend count on the process
identified by <span class="code">Suspendee</span>.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If the process identified by <span class="code">Suspendee</span> is not alive.
</dd>
</dl>
</p></div>
<p><a name="round-1"><span class="bold_code">round(Number) -> integer()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Number = number()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer by rounding <span class="code">Number</span>.</p>
<div class="example"><pre>
> <span class="bold_code">round(5.5).</span>
6</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="self-0"><span class="bold_code">self() -> pid()</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns the pid (process identifier) of the calling process.</p>
<div class="example"><pre>
> <span class="bold_code">self().</span>
<0.26.0></pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="send-2"><span class="bold_code">erlang:send(Dest, Msg) -> Msg</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dest = pid() | port() | RegName | {RegName, Node}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Msg = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> RegName = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Node = node()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sends a message and returns <span class="code">Msg</span>. This is the same as
<span class="code">Dest ! Msg</span>.</p>
<p><span class="code">Dest</span> may be a remote or local pid, a (local) port, a
locally registered name, or a tuple <span class="code">{RegName, Node}</span>
for a registered name at another node.</p>
</p></div>
<p><a name="send-3"><span class="bold_code">erlang:send(Dest, Msg, [Option]) -> Res</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dest = pid() | port() | RegName | {RegName, Node}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> RegName = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Node = node()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Msg = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = nosuspend | noconnect</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Res = ok | nosuspend | noconnect</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sends a message and returns <span class="code">ok</span>, or does not send
the message but returns something else (see below). Otherwise
the same as
<span class="bold_code"><a href="#send-2">erlang:send/2</a></span>. See
also
<span class="bold_code"><a href="#send_nosuspend-2">erlang:send_nosuspend/2,3</a></span>.
for more detailed explanation and warnings.</p>
<p>The possible options are:</p>
<dl>
<dt><strong><span class="code">nosuspend</span></strong></dt>
<dd>
<p>If the sender would have to be suspended to do the send,
<span class="code">nosuspend</span> is returned instead.</p>
</dd>
<dt><strong><span class="code">noconnect</span></strong></dt>
<dd>
<p>If the destination node would have to be auto-connected
before doing the send, <span class="code">noconnect</span> is returned
instead.</p>
</dd>
</dl>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>As with <span class="code">erlang:send_nosuspend/2,3</span>: Use with extreme
care!</p>
</p></div>
</div>
</p></div>
<p><a name="send_after-3"><span class="bold_code">erlang:send_after(Time, Dest, Msg) -> TimerRef</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Time = integer() >= 0</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> 0 <= Time <= 4294967295</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Dest = pid() | RegName </span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> LocalPid = pid() (of a process, alive or dead, on the local node)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Msg = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">TimerRef = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Starts a timer which will send the message <span class="code">Msg</span>
to <span class="code">Dest</span> after <span class="code">Time</span> milliseconds.</p>
<p>If <span class="code">Dest</span> is an atom, it is supposed to be the name of
a registered process. The process referred to by the name is
looked up at the time of delivery. No error is given if
the name does not refer to a process.</p>
<p>If <span class="code">Dest</span> is a pid, the timer will be automatically
canceled if the process referred to by the pid is not alive,
or when the process exits. This feature was introduced in
erts version 5.4.11. Note that timers will not be
automatically canceled when <span class="code">Dest</span> is an atom.</p>
<p>See also
<span class="bold_code"><a href="#start_timer-3">erlang:start_timer/3</a></span>,
<span class="bold_code"><a href="#cancel_timer-1">erlang:cancel_timer/1</a></span>,
and
<span class="bold_code"><a href="#read_timer-1">erlang:read_timer/1</a></span>.</p>
<p>Failure: <span class="code">badarg</span> if the arguments does not satisfy
the requirements specified above.</p>
</p></div>
<p><a name="send_nosuspend-2"></a><span class="bold_code">erlang:send_nosuspend(Dest, Msg) -> boolean()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Dest = dst()</span></div>
<div class="REFTYPES"><span class="bold_code">Msg = term()</span></div>
<div class="REFTYPES">
<span class="bold_code">dst() = pid()<br> | port()<br> | (RegName :: atom())<br> | {RegName :: atom(), Node :: node()}</span><br>
</div>
</div></p>
<div class="REFBODY"><p>
<p>The same as
<span class="bold_code"><a href="#send-3">erlang:send(Dest, Msg, [nosuspend])</a></span>, but returns <span class="code">true</span> if
the message was sent and <span class="code">false</span> if the message was not
sent because the sender would have had to be suspended.</p>
<p>This function is intended for send operations towards an
unreliable remote node without ever blocking the sending
(Erlang) process. If the connection to the remote node
(usually not a real Erlang node, but a node written in C or
Java) is overloaded, this function <strong>will not send the message</strong> but return <span class="code">false</span> instead.</p>
<p>The same happens, if <span class="code">Dest</span> refers to a local port that
is busy. For all other destinations (allowed for the ordinary
send operator <span class="code">'!'</span>) this function sends the message and
returns <span class="code">true</span>.</p>
<p>This function is only to be used in very rare circumstances
where a process communicates with Erlang nodes that can
disappear without any trace causing the TCP buffers and
the drivers queue to be over-full before the node will actually
be shut down (due to tick timeouts) by <span class="code">net_kernel</span>. The
normal reaction to take when this happens is some kind of
premature shutdown of the other node.</p>
<p>Note that ignoring the return value from this function would
result in <strong>unreliable</strong> message passing, which is
contradictory to the Erlang programming model. The message is
<strong>not</strong> sent if this function returns <span class="code">false</span>.</p>
<p>Note also that in many systems, transient states of
overloaded queues are normal. The fact that this function
returns <span class="code">false</span> does not in any way mean that the other
node is guaranteed to be non-responsive, it could be a
temporary overload. Also a return value of <span class="code">true</span> does
only mean that the message could be sent on the (TCP) channel
without blocking, the message is not guaranteed to have
arrived at the remote node. Also in the case of a disconnected
non-responsive node, the return value is <span class="code">true</span> (mimics
the behaviour of the <span class="code">!</span> operator). The expected
behaviour as well as the actions to take when the function
returns <span class="code">false</span> are application and hardware specific.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>Use with extreme care!</p>
</p></div>
</div>
</p></div>
<p><a name="send_nosuspend-3"></a><span class="bold_code">erlang:send_nosuspend(Dest, Msg, Options) -> boolean()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Dest = dst()</span></div>
<div class="REFTYPES"><span class="bold_code">Msg = term()</span></div>
<div class="REFTYPES"><span class="bold_code">Options = [noconnect]</span></div>
<div class="REFTYPES">
<span class="bold_code">dst() = pid()<br> | port()<br> | (RegName :: atom())<br> | {RegName :: atom(), Node :: node()}</span><br>
</div>
</div></p>
<div class="REFBODY"><p>
<p>The same as
<span class="bold_code"><a href="#send-3">erlang:send(Dest, Msg, [nosuspend | Options])</a></span>,
but with boolean return value.</p>
<p>This function behaves like
<span class="bold_code"><a href="#send_nosuspend-2">erlang:send_nosuspend/2)</a></span>,
but takes a third parameter, a list of options. The only
currently implemented option is <span class="code">noconnect</span>. The option
<span class="code">noconnect</span> makes the function return <span class="code">false</span> if
the remote node is not currently reachable by the local
node. The normal behaviour is to try to connect to the node,
which may stall the process for a shorter period. The use of
the <span class="code">noconnect</span> option makes it possible to be
absolutely sure not to get even the slightest delay when
sending to a remote process. This is especially useful when
communicating with nodes who expect to always be
the connecting part (i.e. nodes written in C or Java).</p>
<p>Whenever the function returns <span class="code">false</span> (either when a
suspend would occur or when <span class="code">noconnect</span> was specified and
the node was not already connected), the message is guaranteed
<strong>not</strong> to have been sent.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>Use with extreme care!</p>
</p></div>
</div>
</p></div>
<p><a name="set_cookie-2"></a><span class="bold_code">erlang:set_cookie(Node, Cookie) -> true</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Cookie = atom()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Sets the magic cookie of <span class="code">Node</span> to the atom
<span class="code">Cookie</span>. If <span class="code">Node</span> is the local node, the function
also sets the cookie of all other unknown nodes to
<span class="code">Cookie</span> (see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','doc/reference_manual','distributed.html');">Distributed Erlang</a></span> in the Erlang Reference Manual).</p>
<p>Failure: <span class="code">function_clause</span> if the local node is not
alive.</p>
</p></div>
<p><a name="setelement-3"><span class="bold_code">setelement(Index, Tuple1, Value) -> Tuple2</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Index = 1..tuple_size(Tuple1)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Tuple1 = Tuple2 = tuple()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Value = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a tuple which is a copy of the argument <span class="code">Tuple1</span>
with the element given by the integer argument <span class="code">Index</span>
(the first element is the element with index 1) replaced by
the argument <span class="code">Value</span>.</p>
<div class="example"><pre>
> <span class="bold_code">setelement(2, {10, green, bottles}, red).</span>
{10,red,bottles}</pre></div>
</p></div>
<p><a name="size-1"><span class="bold_code">size(Item) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Item = tuple() | binary()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer which is the size of the argument
<span class="code">Item</span>, which must be either a tuple or a binary.</p>
<div class="example"><pre>
> <span class="bold_code">size({morni, mulle, bwange}).</span>
3</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="spawn-1"></a><span class="bold_code">spawn(Fun) -> pid()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list <span class="code">[]</span>. Otherwise works
like <span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn-2"></a><span class="bold_code">spawn(Node, Fun) -> pid()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list <span class="code">[]</span> on <span class="code">Node</span>. If
<span class="code">Node</span> does not exist, a useless pid is returned.
Otherwise works like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn-3"><span class="bold_code">spawn(Module, Function, Args) -> pid()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Args = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Module:Function</span> to <span class="code">Args</span>. The new process
created will be placed in the system scheduler queue and be
run some time later.</p>
<p><span class="code">error_handler:undefined_function(Module, Function, Args)</span> is evaluated by the new process if
<span class="code">Module:Function/Arity</span> does not exist (where
<span class="code">Arity</span> is the length of <span class="code">Args</span>). The error handler
can be redefined (see
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>).
If <span class="code">error_handler</span> is undefined, or the user has
redefined the default <span class="code">error_handler</span> its replacement is
undefined, a failure with the reason <span class="code">undef</span> will occur.</p>
<div class="example"><pre>
> <span class="bold_code">spawn(speed, regulator, [high_speed, thin_cut]).</span>
<0.13.1></pre></div>
</p></div>
<p><a name="spawn-4"></a><span class="bold_code">spawn(Node, Module, Function, Args) -> pid()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Module = module()</span></div>
<div class="REFTYPES"><span class="bold_code">Function = atom()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Module:Function</span> to <span class="code">Args</span> on <span class="code">Node</span>. If
<span class="code">Node</span> does not exists, a useless pid is returned.
Otherwise works like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_link-1"></a><span class="bold_code">spawn_link(Fun) -> pid()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list []. A link is created between
the calling process and the new process, atomically.
Otherwise works like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_link-2"></a><span class="bold_code">spawn_link(Node, Fun) -> pid()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list [] on <span class="code">Node</span>. A link is
created between the calling process and the new process,
atomically. If <span class="code">Node</span> does not exist, a useless pid is
returned (and due to the link, an exit signal with exit
reason <span class="code">noconnection</span> will be received). Otherwise works
like <span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_link-3"><span class="bold_code">spawn_link(Module, Function, Args) -> pid()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Args = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Module:Function</span> to <span class="code">Args</span>. A link is created
between the calling process and the new process, atomically.
Otherwise works like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_link-4"></a><span class="bold_code">spawn_link(Node, Module, Function, Args) -> pid()</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Module = module()</span></div>
<div class="REFTYPES"><span class="bold_code">Function = atom()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Module:Function</span> to <span class="code">Args</span> on <span class="code">Node</span>. A
link is created between the calling process and the new
process, atomically. If <span class="code">Node</span> does not exist, a useless
pid is returned (and due to the link, an exit signal with exit
reason <span class="code">noconnection</span> will be received). Otherwise works
like <span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_monitor-1"></a><span class="bold_code">spawn_monitor(Fun) -> {pid(), reference()}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list [] and reference for a monitor
created to the new process.
Otherwise works like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_monitor-3"></a><span class="bold_code">spawn_monitor(Module, Function, Args) -> {pid(), reference()}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Module = module()</span></div>
<div class="REFTYPES"><span class="bold_code">Function = atom()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
</div></p>
<div class="REFBODY"><p>
<p>A new process is started by the application
of <span class="code">Module:Function</span> to <span class="code">Args</span>, and the process is
monitored at the same time. Returns the pid and a reference
for the monitor.
Otherwise works like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>.</p>
</p></div>
<p><a name="spawn_opt-2"></a><span class="bold_code">spawn_opt(Fun, Options) -> pid() | {pid(), reference()}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
<div class="REFTYPES"><span class="bold_code">Options = [Option]</span></div>
<div class="REFTYPES"><span class="bold_code">Option = link<br> | monitor<br> | {priority, Level}<br> | {fullsweep_after, Number :: integer() >= 0}<br> | {min_heap_size, Size :: integer() >= 0}<br> | {min_bin_vheap_size, VSize :: integer() >= 0}</span></div>
<div class="REFTYPES"><span class="bold_code">Level = low | normal | high</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list <span class="code">[]</span>. Otherwise
works like
<span class="bold_code"><a href="#spawn_opt-4">spawn_opt/4</a></span>.</p>
<p>If the option <span class="code">monitor</span> is given, the newly created
process will be monitored and both the pid and reference for
the monitor will be returned.</p>
</p></div>
<p><a name="spawn_opt-3"></a><span class="bold_code">spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Fun = function()</span></div>
<div class="REFTYPES"><span class="bold_code">Options = [Option]</span></div>
<div class="REFTYPES"><span class="bold_code">Option = link<br> | monitor<br> | {priority, Level}<br> | {fullsweep_after, Number :: integer() >= 0}<br> | {min_heap_size, Size :: integer() >= 0}<br> | {min_bin_vheap_size, VSize :: integer() >= 0}</span></div>
<div class="REFTYPES"><span class="bold_code">Level = low | normal | high</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Fun</span> to the empty list <span class="code">[]</span> on <span class="code">Node</span>. If
<span class="code">Node</span> does not exist, a useless pid is returned.
Otherwise works like
<span class="bold_code"><a href="#spawn_opt-4">spawn_opt/4</a></span>.</p>
</p></div>
<p><a name="spawn_opt-4"></a><span class="bold_code">spawn_opt(Module, Function, Args, Options) -><br> pid() | {pid(), reference()}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Module = module()</span></div>
<div class="REFTYPES"><span class="bold_code">Function = atom()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
<div class="REFTYPES"><span class="bold_code">Options = [Option]</span></div>
<div class="REFTYPES"><span class="bold_code">Option = link<br> | monitor<br> | {priority, Level}<br> | {fullsweep_after, Number :: integer() >= 0}<br> | {min_heap_size, Size :: integer() >= 0}<br> | {min_bin_vheap_size, VSize :: integer() >= 0}</span></div>
<div class="REFTYPES"><span class="bold_code">Level = low | normal | high</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Works exactly like
<span class="bold_code"><a href="#spawn-3">spawn/3</a></span>, except that an
extra option list is given when creating the process.</p>
<p>If the option <span class="code">monitor</span> is given, the newly created
process will be monitored and both the pid and reference for
the monitor will be returned.</p>
<dl>
<dt><strong><span class="code">link</span></strong></dt>
<dd>
<p>Sets a link to the parent process (like
<span class="code">spawn_link/3</span> does).</p>
</dd>
<dt><strong><span class="code">monitor</span></strong></dt>
<dd>
<p>Monitor the new process (just like
<span class="bold_code"><a href="#monitor-2">monitor/2</a></span> does).</p>
</dd>
<dt><strong><span class="code">{priority, Level}</span></strong></dt>
<dd>
<p>Sets the priority of the new process. Equivalent to
executing
<span class="bold_code"><a href="#process_flag_priority">process_flag(priority, Level)</a></span> in the start function of the new process,
except that the priority will be set before the process is
selected for execution for the first time. For more information
on priorities see
<span class="bold_code"><a href="#process_flag_priority">process_flag(priority, Level)</a></span>.</p>
</dd>
<dt><strong><span class="code">{fullsweep_after, Number}</span></strong></dt>
<dd>
<p>This option is only useful for performance tuning.
In general, you should not use this option unless you
know that there is problem with execution times and/or
memory consumption, and you should measure to make sure
that the option improved matters.
</p>
<p>The Erlang runtime system uses a generational garbage
collection scheme, using an "old heap" for data that has
survived at least one garbage collection. When there is
no more room on the old heap, a fullsweep garbage
collection will be done.</p>
<p>The <span class="code">fullsweep_after</span> option makes it possible to
specify the maximum number of generational collections
before forcing a fullsweep even if there is still room on
the old heap. Setting the number to zero effectively
disables the general collection algorithm, meaning that
all live data is copied at every garbage collection.</p>
<p>Here are a few cases when it could be useful to change
<span class="code">fullsweep_after</span>. Firstly, if binaries that are no
longer used should be thrown away as soon as possible.
(Set <span class="code">Number</span> to zero.) Secondly, a process that
mostly have short-lived data will be fullsweeped seldom
or never, meaning that the old heap will contain mostly
garbage. To ensure a fullsweep once in a while, set
<span class="code">Number</span> to a suitable value such as 10 or 20.
Thirdly, in embedded systems with limited amount of RAM
and no virtual memory, one might want to preserve memory
by setting <span class="code">Number</span> to zero. (The value may be set
globally, see
<span class="bold_code"><a href="#system_flag-2">erlang:system_flag/2</a></span>.)</p>
</dd>
<dt><strong><span class="code">{min_heap_size, Size}</span></strong></dt>
<dd>
<p>This option is only useful for performance tuning.
In general, you should not use this option unless you
know that there is problem with execution times and/or
memory consumption, and you should measure to make sure
that the option improved matters.
</p>
<p>Gives a minimum heap size in words. Setting this value
higher than the system default might speed up some
processes because less garbage collection is done.
Setting too high value, however, might waste memory and
slow down the system due to worse data locality.
Therefore, it is recommended to use this option only for
fine-tuning an application and to measure the execution
time with various <span class="code">Size</span> values.</p>
</dd>
<dt><strong><span class="code">{min_bin_vheap_size, VSize}</span></strong></dt>
<dd>
<p>This option is only useful for performance tuning.
In general, you should not use this option unless you
know that there is problem with execution times and/or
memory consumption, and you should measure to make sure
that the option improved matters.
</p>
<p>Gives a minimum binary virtual heap size in words. Setting this value
higher than the system default might speed up some
processes because less garbage collection is done.
Setting too high value, however, might waste memory.
Therefore, it is recommended to use this option only for
fine-tuning an application and to measure the execution
time with various <span class="code">VSize</span> values.</p>
</dd>
</dl>
</p></div>
<p><a name="spawn_opt-5"></a><span class="bold_code">spawn_opt(Node, Module, Function, Args, Options) -><br> pid() | {pid(), reference()}</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Node = node()</span></div>
<div class="REFTYPES"><span class="bold_code">Module = module()</span></div>
<div class="REFTYPES"><span class="bold_code">Function = atom()</span></div>
<div class="REFTYPES"><span class="bold_code">Args = [term()]</span></div>
<div class="REFTYPES"><span class="bold_code">Options = [Option]</span></div>
<div class="REFTYPES"><span class="bold_code">Option = link<br> | monitor<br> | {priority, Level}<br> | {fullsweep_after, Number :: integer() >= 0}<br> | {min_heap_size, Size :: integer() >= 0}<br> | {min_bin_vheap_size, VSize :: integer() >= 0}</span></div>
<div class="REFTYPES"><span class="bold_code">Level = low | normal | high</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Returns the pid of a new process started by the application
of <span class="code">Module:Function</span> to <span class="code">Args</span> on <span class="code">Node</span>. If
<span class="code">Node</span> does not exist, a useless pid is returned.
Otherwise works like
<span class="bold_code"><a href="#spawn_opt-4">spawn_opt/4</a></span>.</p>
</p></div>
<p><a name="split_binary-2"><span class="bold_code">split_binary(Bin, Pos) -> {Bin1, Bin2}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Bin = Bin1 = Bin2 = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Pos = 0..byte_size(Bin)</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a tuple containing the binaries which are the result
of splitting <span class="code">Bin</span> into two parts at position <span class="code">Pos</span>.
This is not a destructive operation. After the operation,
there will be three binaries altogether.</p>
<div class="example"><pre>
> <span class="bold_code">B = list_to_binary("0123456789").</span>
<<"0123456789">>
> <span class="bold_code">byte_size(B).</span>
10
> <span class="bold_code">{B1, B2} = split_binary(B,3).</span>
{<<"012">>,<<"3456789">>}
> <span class="bold_code">byte_size(B1).</span>
3
> <span class="bold_code">byte_size(B2).</span>
7</pre></div>
</p></div>
<p><a name="start_timer-3"><span class="bold_code">erlang:start_timer(Time, Dest, Msg) -> TimerRef</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Time = integer() >= 0</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> 0 <= Time <= 4294967295</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Dest = LocalPid | RegName </span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> LocalPid = pid() (of a process, alive or dead, on the local node)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> RegName = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Msg = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">TimerRef = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Starts a timer which will send the message
<span class="code">{timeout, TimerRef, Msg}</span> to <span class="code">Dest</span>
after <span class="code">Time</span> milliseconds.</p>
<p>If <span class="code">Dest</span> is an atom, it is supposed to be the name of
a registered process. The process referred to by the name is
looked up at the time of delivery. No error is given if
the name does not refer to a process.</p>
<p>If <span class="code">Dest</span> is a pid, the timer will be automatically
canceled if the process referred to by the pid is not alive,
or when the process exits. This feature was introduced in
erts version 5.4.11. Note that timers will not be
automatically canceled when <span class="code">Dest</span> is an atom.</p>
<p>See also
<span class="bold_code"><a href="#send_after-3">erlang:send_after/3</a></span>,
<span class="bold_code"><a href="#cancel_timer-1">erlang:cancel_timer/1</a></span>,
and
<span class="bold_code"><a href="#read_timer-1">erlang:read_timer/1</a></span>.</p>
<p>Failure: <span class="code">badarg</span> if the arguments does not satisfy
the requirements specified above.</p>
</p></div>
<p><a name="statistics-1"><span class="bold_code">statistics(Type) -> Res</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Type, Res -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>All times are in milliseconds unless otherwise specified.</p>
<p>Returns information about the system as specified by
<span class="code">Type</span>:</p>
<dl>
<dt><strong><span class="code">context_switches</span></strong></dt>
<dd>
<p>Returns <span class="code">{ContextSwitches, 0}</span>, where
<span class="code">ContextSwitches</span> is the total number of context
switches since the system started.</p>
</dd>
<dt><strong><a name="statistics_exact_reductions"><span class="code">exact_reductions</span></a></strong></dt>
<dd>
<p>Returns
<span class="code">{Total_Exact_Reductions, Exact_Reductions_Since_Last_Call}</span>.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p><span class="code">statistics(exact_reductions)</span> is
a more expensive operation than
<span class="bold_code"><a href="#statistics_reductions">statistics(reductions)</a></span>
especially on an Erlang machine with SMP support.</p>
</p></div>
</div>
</dd>
<dt><strong><span class="code">garbage_collection</span></strong></dt>
<dd>
<p>Returns <span class="code">{Number_of_GCs, Words_Reclaimed, 0}</span>. This
information may not be valid for all implementations.</p>
<div class="example"><pre>
> <span class="bold_code">statistics(garbage_collection).</span>
{85,23961,0}
</pre></div>
</dd>
<dt><strong><span class="code">io</span></strong></dt>
<dd>
<p>Returns <span class="code">{{input, Input}, {output, Output}}</span>,
where <span class="code">Input</span> is the total number of bytes received
through ports, and <span class="code">Output</span> is the total number of
bytes output to ports.</p>
</dd>
<dt><strong><a name="statistics_reductions"><span class="code">reductions</span></a></strong></dt>
<dd>
<p>Returns
<span class="code">{Total_Reductions, Reductions_Since_Last_Call}</span>.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>From erts version 5.5 (OTP release R11B)
this value does not include reductions performed in current
time slices of currently scheduled processes. If an
exact value is wanted, use
<span class="bold_code"><a href="#statistics_exact_reductions">statistics(exact_reductions)</a></span>.</p>
</p></div>
</div>
<div class="example"><pre>
> <span class="bold_code">statistics(reductions).</span>
{2046,11}
</pre></div>
</dd>
<dt><strong><span class="code">run_queue</span></strong></dt>
<dd>
<p>Returns the length of the run queue, that is, the number
of processes that are ready to run.</p>
</dd>
<dt><strong><span class="code">runtime</span></strong></dt>
<dd>
<p>Returns <span class="code">{Total_Run_Time, Time_Since_Last_Call}</span>.
Note that the run-time is the sum of the run-time for all
threads in the Erlang run-time system and may therefore be greater
than the wall-clock time.</p>
<div class="example"><pre>
> <span class="bold_code">statistics(runtime).</span>
{1690,1620}
</pre></div>
</dd>
<dt><strong><a name="statistics_scheduler_wall_time"><span class="code">scheduler_wall_time</span></a></strong></dt>
<dd>
<p>Returns a list of tuples with
<span class="code">{SchedulerId, ActiveTime, TotalTime}</span>, where <span class="code">SchedulerId</span> is an integer id of the scheduler, <span class="code">ActiveTime</span> is
the duration the scheduler has been busy, <span class="code">TotalTime</span> is the total time duration since
<span class="bold_code"><a href="#system_flag_scheduler_wall_time">scheduler_wall_time</a></span>
activation. The time unit is not defined and may be subject to change
between releases, operating systems and system restarts.
<span class="code">scheduler_wall_time</span> should only be used to calculate relative
values for scheduler-utilization. <span class="code">ActiveTime</span> can never exceed <span class="code">TotalTime</span>.
</p>
<p>The definition of a busy scheduler is when it is not idle or not
scheduling (selecting) a process or port, meaning; executing process
code, executing linked-in-driver or NIF code, executing
built-in-functions or any other runtime handling, garbage collecting
or handling any other memory management. Note, a scheduler may also be
busy even if the operating system has scheduled out the scheduler
thread.
</p>
<p>
Returns <span class="code">undefined</span> if the system flag <span class="bold_code"><a href="#system_flag_scheduler_wall_time">
scheduler_wall_time</a></span> is turned off.
</p>
<p>The list of scheduler information is unsorted and may appear in different order
between calls.
</p>
<p>Using <span class="code">scheduler_wall_time</span> to calculate scheduler utilization.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:system_flag(scheduler_wall_time, true).</span>
false
> <span class="bold_code">Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</span>
ok
</pre></div>
<p>Some time later we will take another snapshot and calculate scheduler-utilization per scheduler.</p>
<div class="example"><pre>
> <span class="bold_code">Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</span>
ok
> <span class="bold_code">lists:map(fun({{I, A0, T0}, {I, A1, T1}}) ->
{I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).</span>
[{1,0.9743474730177548},
{2,0.9744843782751444},
{3,0.9995902361669045},
{4,0.9738012596572161},
{5,0.9717956667018103},
{6,0.9739235846420741},
{7,0.973237033077876},
{8,0.9741297293248656}]
</pre></div>
<p>Using the same snapshots to calculate a total scheduler-utilization.</p>
<div class="example"><pre>
> <span class="bold_code">{A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) ->
{Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T.</span>
0.9769136803764825
</pre></div>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p><span class="code">scheduler_wall_time</span> is by default disabled. Use <span class="code">erlang:system_flag(scheduler_wall_time, true)</span> to enable it. </p>
</p></div>
</div>
</dd>
<dt><strong><span class="code">wall_clock</span></strong></dt>
<dd>
<p>Returns
<span class="code">{Total_Wallclock_Time, Wallclock_Time_Since_Last_Call}</span>.
<span class="code">wall_clock</span> can be used in the same manner as
<span class="code">runtime</span>, except that real time is measured as
opposed to runtime or CPU time.</p>
</dd>
</dl>
</p></div>
<p><a name="suspend_process-2"><span class="bold_code">erlang:suspend_process(Suspendee, OptList) -> boolean()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Suspendee = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">OptList = [Opt]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Opt = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Increases the suspend count on the process identified by
<span class="code">Suspendee</span> and puts it in the suspended state if it isn't
already in the suspended state. A suspended process will not be
scheduled for execution until the process has been resumed.
</p>
<p>A process can be suspended by multiple processes and can
be suspended multiple times by a single process. A suspended
process will not leave the suspended state until its suspend
count reach zero. The suspend count of <span class="code">Suspendee</span> is
decreased when
<span class="bold_code"><a href="#resume_process-1">erlang:resume_process(Suspendee)</a></span>
is called by the same process that called
<span class="code">erlang:suspend_process(Suspendee)</span>. All increased suspend
counts on other processes acquired by a process will automatically be
decreased when the process terminates.</p>
<p>Currently the following options (<span class="code">Opt</span>s) are available:</p>
<dl>
<dt><strong><span class="code">asynchronous</span></strong></dt>
<dd>
A suspend request is sent to the process identified by
<span class="code">Suspendee</span>. <span class="code">Suspendee</span> will eventually suspend
unless it is resumed before it was able to suspend. The caller
of <span class="code">erlang:suspend_process/2</span> will return immediately,
regardless of whether the <span class="code">Suspendee</span> has suspended yet
or not. Note that the point in time when the <span class="code">Suspendee</span>
will actually suspend cannot be deduced from other events
in the system. The only guarantee given is that the
<span class="code">Suspendee</span> will <strong>eventually</strong> suspend (unless it
is resumed). If the <span class="code">asynchronous</span> option has <strong>not</strong>
been passed, the caller of <span class="code">erlang:suspend_process/2</span> will
be blocked until the <span class="code">Suspendee</span> has actually suspended.
</dd>
<dt><strong><span class="code">unless_suspending</span></strong></dt>
<dd>
The process identified by <span class="code">Suspendee</span> will be suspended
unless the calling process already is suspending the
<span class="code">Suspendee</span>. If <span class="code">unless_suspending</span> is combined
with the <span class="code">asynchronous</span> option, a suspend request will be
sent unless the calling process already is suspending the
<span class="code">Suspendee</span> or if a suspend request already has been sent
and is in transit. If the calling process already is suspending
the <span class="code">Suspendee</span>, or if combined with the <span class="code">asynchronous</span>
option and a send request already is in transit,
<span class="code">false</span> is returned and the suspend count on <span class="code">Suspendee</span>
will remain unchanged.
</dd>
</dl>
<p>If the suspend count on the process identified by
<span class="code">Suspendee</span> was increased, <span class="code">true</span> is returned; otherwise,
<span class="code">false</span> is returned.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging only.</p>
</p></div>
</div>
<p>Failures:</p>
<dl>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">Suspendee</span> isn't a process identifier.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If the process identified by <span class="code">Suspendee</span> is same the process as
the process calling <span class="code">erlang:suspend_process/2</span>.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If the process identified by <span class="code">Suspendee</span> is not alive.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If the process identified by <span class="code">Suspendee</span> resides on another node.
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
If <span class="code">OptList</span> isn't a proper list of valid <span class="code">Opt</span>s.
</dd>
<dt><strong><span class="code">system_limit</span></strong></dt>
<dd>
If the process identified by <span class="code">Suspendee</span> has been suspended more
times by the calling process than can be represented by the
currently used internal data structures. The current system limit
is larger than 2 000 000 000 suspends, and it will never be less
than that.
</dd>
</dl>
</p></div>
<p><a name="suspend_process-1"></a><span class="bold_code">erlang:suspend_process(Suspendee) -> true</span><br><div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES"><span class="bold_code">Suspendee = pid()</span></div>
</div></p>
<div class="REFBODY"><p>
<p>Suspends the process identified by <span class="code">Suspendee</span>. The
same as calling
<span class="bold_code"><a href="#suspend_process-2">erlang:suspend_process(Suspendee, [])</a></span>. For more information see the documentation of <span class="bold_code"><a href="#suspend_process-2">erlang:suspend_process/2</a></span>.
</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This BIF is intended for debugging only.</p>
</p></div>
</div>
</p></div>
<p><a name="system_flag-2"><span class="bold_code">erlang:system_flag(Flag, Value) -> OldValue</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Flag, Value, OldValue -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>The
<span class="bold_code"><a href="#system_flag_cpu_topology">cpu_topology</a></span>,
and
<span class="bold_code"><a href="#system_flag_scheduler_bind_type">scheduler_bind_type</a></span>
<span class="code">Flag</span>s are <strong>deprecated</strong> and have been scheduled for
removal in erts-5.10/OTP-R16.</p>
</p></div>
</div>
<p>Sets various system properties of the Erlang node. Returns
the old value of the flag.</p>
<dl>
<dt><strong><span class="code">erlang:system_flag(backtrace_depth, Depth)</span></strong></dt>
<dd>
<p>Sets the maximum depth of call stack back-traces in the
exit reason element of <span class="code">'EXIT'</span> tuples.</p>
</dd>
<dt><strong><a name="system_flag_cpu_topology"><span class="code">erlang:system_flag(cpu_topology, CpuTopology)</span></a></strong></dt>
<dd>
<p><strong>NOTE:</strong> This argument is <strong>deprecated</strong> and
scheduled for removal in erts-5.10/OTP-R16. Instead of using
this argument you are advised to use the <span class="code">erl</span> command
line argument <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sct');">+sct</a></span>.
When this argument has been removed a final CPU topology to use
will be determined at emulator boot time.</p>
<p>Sets the user defined <span class="code">CpuTopology</span>. The user defined
CPU topology will override any automatically detected
CPU topology. By passing <span class="code">undefined</span> as <span class="code">CpuTopology</span>
the system will revert back to the CPU topology automatically
detected. The returned value equals the value returned
from <span class="code">erlang:system_info(cpu_topology)</span> before the
change was made.
</p>
<p>The CPU topology is used when binding schedulers to logical
processors. If schedulers are already bound when the CPU
topology is changed, the schedulers will be sent a request
to rebind according to the new CPU topology.
</p>
<p>The user defined CPU topology can also be set by passing
the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sct');">+sct</a></span> command
line argument to <span class="code">erl</span>.
</p>
<p>For information on the <span class="code">CpuTopology</span> type
and more, see the documentation of
<span class="bold_code"><a href="#system_info_cpu_topology">erlang:system_info(cpu_topology)</a></span>,
and the <span class="code">erl</span> <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sct');">+sct</a></span>
and <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt</a></span>
command line flags.
</p>
</dd>
<dt><strong><span class="code">erlang:system_flag(fullsweep_after, Number)</span></strong></dt>
<dd>
<p><span class="code">Number</span> is a non-negative integer which indicates
how many times generational garbage collections can be
done without forcing a fullsweep collection. The value
applies to new processes; processes already running are
not affected.</p>
<p>In low-memory systems (especially without virtual
memory), setting the value to 0 can help to conserve
memory.</p>
<p>An alternative way to set this value is through the
(operating system) environment variable
<span class="code">ERL_FULLSWEEP_AFTER</span>.</p>
</dd>
<dt><strong><span class="code">erlang:system_flag(min_heap_size, MinHeapSize)</span></strong></dt>
<dd>
<p>Sets the default minimum heap size for processes. The
size is given in words. The new <span class="code">min_heap_size</span> only
effects processes spawned after the change of
<span class="code">min_heap_size</span> has been made.
The <span class="code">min_heap_size</span> can be set for individual
processes by use of
<span class="bold_code"><a href="#spawn_opt-4">spawn_opt/N</a></span> or
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>. </p>
</dd>
<dt><strong><span class="code">erlang:system_flag(min_bin_vheap_size, MinBinVHeapSize)</span></strong></dt>
<dd>
<p>Sets the default minimum binary virtual heap size for processes. The
size is given in words. The new <span class="code">min_bin_vhheap_size</span> only
effects processes spawned after the change of
<span class="code">min_bin_vhheap_size</span> has been made.
The <span class="code">min_bin_vheap_size</span> can be set for individual
processes by use of
<span class="bold_code"><a href="#spawn_opt-4">spawn_opt/N</a></span> or
<span class="bold_code"><a href="#process_flag-2">process_flag/2</a></span>. </p>
</dd>
<dt><strong><a name="system_flag_multi_scheduling"><span class="code">erlang:system_flag(multi_scheduling, BlockState)</span></a></strong></dt>
<dd>
<p><span class="code">BlockState = block | unblock</span></p>
<p>If multi-scheduling is enabled, more than one scheduler
thread is used by the emulator. Multi-scheduling can be
blocked. When multi-scheduling has been blocked, only
one scheduler thread will schedule Erlang processes.</p>
<p>If <span class="code">BlockState =:= block</span>, multi-scheduling will
be blocked. If <span class="code">BlockState =:= unblock</span> and no-one
else is blocking multi-scheduling and this process has
only blocked one time, multi-scheduling will be unblocked.
One process can block multi-scheduling multiple times.
If a process has blocked multiple times, it has to
unblock exactly as many times as it has blocked before it
has released its multi-scheduling block. If a process that
has blocked multi-scheduling exits, it will release its
blocking of multi-scheduling.</p>
<p>The return values are <span class="code">disabled</span>, <span class="code">blocked</span>,
or <span class="code">enabled</span>. The returned value describes the
state just after the call to
<span class="code">erlang:system_flag(multi_scheduling, BlockState)</span>
has been made. The return values are described in the
documentation of <span class="bold_code"><a href="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</a></span>.</p>
<p><strong>NOTE</strong>: Blocking of multi-scheduling should normally
not be needed. If you feel that you need to
block multi-scheduling, think through the
problem at least a couple of times again.
Blocking multi-scheduling should only be used
as a last resort since it will most likely be
a <strong>very inefficient</strong> way to solve the
problem.</p>
<p>See also <span class="bold_code"><a href="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</a></span>,
<span class="bold_code"><a href="#system_info_multi_scheduling_blockers">erlang:system_info(multi_scheduling_blockers)</a></span>, and
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span>.</p>
</dd>
<dt><strong><a name="system_flag_scheduler_bind_type"><span class="code">erlang:system_flag(scheduler_bind_type, How)</span></a></strong></dt>
<dd>
<p><strong>NOTE:</strong> This argument is <strong>deprecated</strong> and
scheduled for removal in erts-5.10/OTP-R16. Instead of using
this argument you are advised to use the <span class="code">erl</span> command
line argument <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt</a></span>.
When this argument has been removed a final scheduler bind type
to use will be determined at emulator boot time.</p>
<p>Controls if and how schedulers are bound to logical
processors.</p>
<p>When <span class="code">erlang:system_flag(scheduler_bind_type, How)</span> is
called, an asynchronous signal is sent to all schedulers
online which causes them to try to bind or unbind as requested.
<strong>NOTE:</strong> If a scheduler fails to bind, this
will often be silently ignored. This since it isn't always
possible to verify valid logical processor identifiers. If
an error is reported, it will be reported to the
<span class="code">error_logger</span>. If you want to verify that the
schedulers actually have bound as requested, call
<span class="bold_code"><a href="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</a></span>.
</p>
<p>Schedulers can currently only be bound on newer Linux,
Solaris, FreeBSD, and Windows systems, but more systems will be
supported in the future.
</p>
<p>In order for the runtime system to be able to bind schedulers,
the CPU topology needs to be known. If the runtime system fails
to automatically detect the CPU topology, it can be defined.
For more information on how to define the CPU topology, see
the <span class="code">erl</span> <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sct');">+sct</a></span> command
line flag.
</p>
<p>The runtime system will by default <strong>not</strong> bind schedulers
to logical processors.
</p>
<p><strong>NOTE:</strong> If the Erlang runtime system is the only
operating system process that binds threads to logical processors,
this improves the performance of the runtime system. However,
if other operating system processes (as for example another Erlang
runtime system) also bind threads to logical processors, there
might be a performance penalty instead. In some cases this
performance penalty might be severe. If this is the case, you
are advised to not bind the schedulers.</p>
<p>Schedulers can be bound in different ways. The <span class="code">How</span>
argument determines how schedulers are bound. <span class="code">How</span> can
currently be one of:</p>
<dl>
<dt><strong><span class="code">unbound</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt u</a></span>.
</p></dd>
<dt><strong><span class="code">no_spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt ns</a></span>.
</p></dd>
<dt><strong><span class="code">thread_spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt ts</a></span>.
</p></dd>
<dt><strong><span class="code">processor_spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt ps</a></span>.
</p></dd>
<dt><strong><span class="code">spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt s</a></span>.
</p></dd>
<dt><strong><span class="code">no_node_thread_spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt nnts</a></span>.
</p></dd>
<dt><strong><span class="code">no_node_processor_spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt nnps</a></span>.
</p></dd>
<dt><strong><span class="code">thread_no_node_processor_spread</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt tnnps</a></span>.
</p></dd>
<dt><strong><span class="code">default_bind</span></strong></dt>
<dd><p>Same as the <span class="code">erl</span> command line argument
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt db</a></span>.
</p></dd>
</dl>
<p>The value returned equals <span class="code">How</span> before the
<span class="code">scheduler_bind_type</span> flag was changed.</p>
<p>Failure:</p>
<dl>
<dt><strong><span class="code">notsup</span></strong></dt>
<dd>
<p>If binding of schedulers is not supported.</p>
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
<p>If <span class="code">How</span> isn't one of the documented alternatives.</p>
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
<p>If no CPU topology information is available.</p>
</dd>
</dl>
<p>The scheduler bind type can also be set by passing
the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt</a></span> command
line argument to <span class="code">erl</span>.
</p>
<p>For more information, see
<span class="bold_code"><a href="#system_info_scheduler_bind_type">erlang:system_info(scheduler_bind_type)</a></span>,
<span class="bold_code"><a href="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</a></span>,
the <span class="code">erl</span> <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt</a></span>
and <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sct');">+sct</a></span> command line
flags.
</p>
</dd>
<dt><strong><a name="system_flag_scheduler_wall_time"><span class="code">erlang:system_flag(scheduler_wall_time, Boolean)</span></a></strong></dt>
<dd>
<p>Turns on/off scheduler wall time measurements. </p>
<p>For more information see,
<span class="bold_code"><a href="#statistics_scheduler_wall_time">erlang:statistics(scheduler_wall_time)</a></span>.
</p>
</dd>
<dt><strong><a name="system_flag_schedulers_online"><span class="code">erlang:system_flag(schedulers_online, SchedulersOnline)</span></a></strong></dt>
<dd>
<p>Sets the amount of schedulers online. Valid range is
1 <= SchedulerId <= erlang:system_info(schedulers).
</p>
<p>For more information see,
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span>,
and
<span class="bold_code"><a href="#system_info_schedulers_online">erlang:system_info(schedulers_online)</a></span>.
</p>
</dd>
<dt><strong><span class="code">erlang:system_flag(trace_control_word, TCW)</span></strong></dt>
<dd>
<p>Sets the value of the node's trace control word to
<span class="code">TCW</span>. <span class="code">TCW</span> should be an unsigned integer. For
more information see documentation of the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','match_spec.html#set_tcw');">set_tcw</a></span>
function in the match specification documentation in the
ERTS User's Guide.</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The <span class="code">schedulers</span> option has been removed as
of erts version 5.5.3. The number of scheduler
threads is determined at emulator boot time, and
cannot be changed after that.</p>
</p></div>
</div>
</p></div>
<p><a name="system_info-1"><span class="bold_code">erlang:system_info(Type) -> Res</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Type, Res -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns various information about the current system
(emulator) as specified by <span class="code">Type</span>:</p>
<dl>
<dt><strong><a name="system_info_allocated_areas"><span class="code">allocated_areas</span></a></strong></dt>
<dd>
<p>Returns a list of tuples with information about
miscellaneous allocated memory areas.</p>
<p>Each tuple contains an atom describing type of memory as
first element and amount of allocated memory in bytes as
second element. In those cases when there is information
present about allocated and used memory, a third element
is present. This third element contains the amount of
used memory in bytes.</p>
<p><span class="code">erlang:system_info(allocated_areas)</span> is intended
for debugging, and the content is highly implementation
dependent. The content of the results will therefore
change when needed without prior notice.</p>
<p><strong>Note:</strong> The sum of these values is <strong>not</strong>
the total amount of memory allocated by the emulator.
Some values are part of other values, and some memory
areas are not part of the result. If you are interested
in the total amount of memory allocated by the emulator
see <span class="bold_code"><a href="#memory-0">erlang:memory/0,1</a></span>.</p>
</dd>
<dt><strong><a name="system_info_allocator"><span class="code">allocator</span></a></strong></dt>
<dd>
<p>Returns <span class="code">{Allocator, Version, Features, Settings}.</span></p>
<p>Types:</p>
<ul>
<li><span class="code">Allocator = undefined | glibc</span></li>
<li><span class="code">Version = [integer()]</span></li>
<li><span class="code">Features = [atom()]</span></li>
<li><span class="code">Settings = [{Subsystem, [{Parameter, Value}]}]</span></li>
<li><span class="code">Subsystem = atom()</span></li>
<li><span class="code">Parameter = atom()</span></li>
<li><span class="code">Value = term()</span></li>
</ul>
<p>Explanation:</p>
<ul>
<li>
<p><span class="code">Allocator</span> corresponds to the <span class="code">malloc()</span>
implementation used. If <span class="code">Allocator</span> equals
<span class="code">undefined</span>, the <span class="code">malloc()</span> implementation
used could not be identified. Currently
<span class="code">glibc</span> can be identified.</p>
</li>
<li>
<p><span class="code">Version</span> is a list of integers (but not a
string) representing the version of
the <span class="code">malloc()</span> implementation used.</p>
</li>
<li>
<p><span class="code">Features</span> is a list of atoms representing
allocation features used.</p>
</li>
<li>
<p><span class="code">Settings</span> is a list of subsystems, their
configurable parameters, and used values. Settings
may differ between different combinations of
platforms, allocators, and allocation features.
Memory sizes are given in bytes.</p>
</li>
</ul>
<p>See also "System Flags Effecting erts_alloc" in
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html#flags');">erts_alloc(3)</a></span>.</p>
</dd>
<dt><strong><a name="system_info_alloc_util_allocators"><span class="code">alloc_util_allocators</span></a></strong></dt>
<dd>
<p>Returns a list of the names of all allocators
using the ERTS internal <span class="code">alloc_util</span> framework
as atoms. For more information see the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html#alloc_util');">"the
alloc_util framework" section in the
erts_alloc(3)</a></span> documentation.
</p>
</dd>
<dt><strong><a name="system_info_allocator_tuple"><span class="code">{allocator, Alloc}</span></a></strong></dt>
<dd>
<p>Returns information about the specified allocator.
As of erts version 5.6.1 the return value is a list
of <span class="code">{instance, InstanceNo, InstanceInfo}</span> tuples
where <span class="code">InstanceInfo</span> contains information about
a specific instance of the allocator.
If <span class="code">Alloc</span> is not a recognized allocator,
<span class="code">undefined</span> is returned. If <span class="code">Alloc</span> is disabled,
<span class="code">false</span> is returned.</p>
<p><strong>Note:</strong> The information returned is highly
implementation dependent and may be changed, or removed
at any time without prior notice. It was initially
intended as a tool when developing new allocators, but
since it might be of interest for others it has been
briefly documented.</p>
<p>The recognized allocators are listed in
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>.
After reading the <span class="code">erts_alloc(3)</span> documentation,
the returned information
should more or less speak for itself. But it can be worth
explaining some things. Call counts are presented by two
values. The first value is giga calls, and the second
value is calls. <span class="code">mbcs</span>, and <span class="code">sbcs</span> are
abbreviations for, respectively, multi-block carriers, and
single-block carriers. Sizes are presented in bytes. When
it is not a size that is presented, it is the amount of
something. Sizes and amounts are often presented by three
values, the first is current value, the second is maximum
value since the last call to
<span class="code">erlang:system_info({allocator, Alloc})</span>, and
the third is maximum value since the emulator was started.
If only one value is present, it is the current value.
<span class="code">fix_alloc</span> memory block types are presented by two
values. The first value is memory pool size and
the second value used memory size.</p>
</dd>
<dt><strong><a name="system_info_allocator_sizes"><span class="code">{allocator_sizes, Alloc}</span></a></strong></dt>
<dd>
<p>Returns various size information for the specified
allocator. The information returned is a subset of the
information returned by
<span class="bold_code"><a href="#system_info_allocator_tuple">erlang:system_info({allocator, Alloc})</a></span>.
</p>
</dd>
<dt><strong><span class="code">build_type</span></strong></dt>
<dd>
<p>Returns an atom describing the build type of the runtime
system. This is normally the atom <span class="code">opt</span> for optimized.
Other possible return values are <span class="code">debug</span>, <span class="code">purify</span>,
<span class="code">quantify</span>, <span class="code">purecov</span>, <span class="code">gcov</span>, <span class="code">valgrind</span>,
<span class="code">gprof</span>, and <span class="code">lcnt</span>. Possible return values
may be added and/or removed at any time without prior notice.
</p>
</dd>
<dt><strong><span class="code">c_compiler_used</span></strong></dt>
<dd>
<p>Returns a two-tuple describing the C compiler used when
compiling the runtime system. The first element is an
atom describing the name of the compiler, or <span class="code">undefined</span>
if unknown. The second element is a term describing the
version of the compiler, or <span class="code">undefined</span> if unknown.
</p>
</dd>
<dt><strong><span class="code">check_io</span></strong></dt>
<dd>
<p>Returns a list containing miscellaneous information
regarding the emulators internal I/O checking. Note,
the content of the returned list may vary between
platforms and over time. The only thing guaranteed is
that a list is returned.</p>
</dd>
<dt><strong><span class="code">compat_rel</span></strong></dt>
<dd>
<p>Returns the compatibility mode of the local node as
an integer. The integer returned represents the
Erlang/OTP release which the current emulator has been
set to be backward compatible with. The compatibility
mode can be configured at startup by using the command
line flag <span class="code">+R</span>, see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#compat_rel');">erl(1)</a></span>.</p>
</dd>
<dt><strong><a name="system_info_cpu_topology"><span class="code">cpu_topology</span></a></strong></dt>
<dd>
<p>Returns the <span class="code">CpuTopology</span> which currently is used by the
emulator. The CPU topology is used when binding schedulers
to logical processors. The CPU topology used is the
<span class="bold_code"><a href="erlang.html#system_info_cpu_topology_defined">user
defined CPU topology</a></span> if such exists; otherwise, the
<span class="bold_code"><a href="erlang.html#system_info_cpu_topology_detected">automatically
detected CPU topology</a></span> if such exists. If no CPU topology
exists, <span class="code">undefined</span> is returned.</p>
<p>Types:</p>
<ul>
<li><span class="code">CpuTopology = LevelEntryList | undefined</span></li>
<li>
<span class="code">LevelEntryList = [LevelEntry]</span> (all
<span class="code">LevelEntry</span>s of a <span class="code">LevelEntryList</span>
must contain the same <span class="code">LevelTag</span>, except
on the top level where both <span class="code">node</span> and
<span class="code">processor</span> <span class="code">LevelTag</span>s may co-exist)</li>
<li>
<span class="code">LevelEntry = {LevelTag, SubLevel}
| {LevelTag, InfoList, SubLevel}</span>
(<span class="code">{LevelTag, SubLevel}
== {LevelTag, [], SubLevel}</span>)</li>
<li>
<span class="code">LevelTag = node|processor|core|thread</span>
(more <span class="code">LevelTag</span>s may be introduced in
the future)</li>
<li><span class="code">SubLevel = [LevelEntry] | LogicalCpuId</span></li>
<li><span class="code">LogicalCpuId = {logical, integer()}</span></li>
<li>
<span class="code">InfoList = []</span> (the <span class="code">InfoList</span>
may be extended in the future)</li>
</ul>
<p><span class="code">node</span> refers to NUMA (non-uniform memory access)
nodes, and <span class="code">thread</span> refers to hardware threads
(e.g. Intels hyper-threads).</p>
<p>A level in the <span class="code">CpuTopology</span> term can be omitted if
only one entry exists and the <span class="code">InfoList</span> is empty.
</p>
<p><span class="code">thread</span> can only be a sub level to <span class="code">core</span>.
<span class="code">core</span> can be a sub level to either <span class="code">processor</span>
or <span class="code">node</span>. <span class="code">processor</span> can either be on the
top level or a sub level to <span class="code">node</span>. <span class="code">node</span>
can either be on the top level or a sub level to
<span class="code">processor</span>. That is, NUMA nodes can be processor
internal or processor external. A CPU topology can
consist of a mix of processor internal and external
NUMA nodes, as long as each logical CPU belongs to one
and only one NUMA node. Cache hierarchy is not part of
the <span class="code">CpuTopology</span> type yet, but will be in the
future. Other things may also make it into the CPU
topology in the future. In other words, expect the
<span class="code">CpuTopology</span> type to change.
</p>
</dd>
<dt><strong><a name="system_info_cpu_topology_defined"><span class="code">{cpu_topology, defined}</span></a></strong></dt>
<dd>
<p>Returns the user defined <span class="code">CpuTopology</span>. For more
information see the documentation of
the <span class="code">erl</span> <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sct');">+sct</a></span> command
line flag, and the documentation of the
<span class="bold_code"><a href="#system_info_cpu_topology">cpu_topology</a></span>
argument.
</p>
</dd>
<dt><strong><a name="system_info_cpu_topology_detected"><span class="code">{cpu_topology, detected}</span></a></strong></dt>
<dd>
<p>Returns the automatically detected <span class="code">CpuTopology</span>. The
emulator currently only detects the CPU topology on some newer
Linux, Solaris, FreeBSD, and Windows systems. On Windows system with
more than 32 logical processors the CPU topology is not detected.
</p>
<p>For more information see the documentation of the
<span class="bold_code"><a href="#system_info_cpu_topology">cpu_topology</a></span>
argument.
</p>
</dd>
<dt><strong><span class="code">{cpu_topology, used}</span></strong></dt>
<dd>
<p>Returns the <span class="code">CpuTopology</span> which is used by the
emulator. For more information see the
documentation of the
<span class="bold_code"><a href="#system_info_cpu_topology">cpu_topology</a></span>
argument.
</p>
</dd>
<dt><strong><span class="code">creation</span></strong></dt>
<dd>
<p>Returns the creation of the local node as an integer.
The creation is changed when a node is restarted. The
creation of a node is stored in process identifiers, port
identifiers, and references. This makes it (to some
extent) possible to distinguish between identifiers from
different incarnations of a node. Currently valid
creations are integers in the range 1..3, but this may
(probably will) change in the future. If the node is not
alive, 0 is returned.</p>
</dd>
<dt><strong><span class="code">debug_compiled</span></strong></dt>
<dd>
<p>Returns <span class="code">true</span> if the emulator has been debug
compiled; otherwise, <span class="code">false</span>.
</p>
</dd>
<dt><strong><span class="code">dist</span></strong></dt>
<dd>
<p>Returns a binary containing a string of distribution
information formatted as in Erlang crash dumps. For more
information see the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','crash_dump.html');">"How to interpret the Erlang crash dumps"</a></span>
chapter in the ERTS User's Guide.</p>
</dd>
<dt><strong><span class="code">dist_ctrl</span></strong></dt>
<dd>
<p>Returns a list of tuples
<span class="code">{Node, ControllingEntity}</span>, one entry for each
connected remote node. The <span class="code">Node</span> is the name of the
node and the <span class="code">ControllingEntity</span> is the port or pid
responsible for the communication to that node. More
specifically, the <span class="code">ControllingEntity</span> for nodes
connected via TCP/IP (the normal case) is the socket
actually used in communication with the specific node.</p>
</dd>
<dt><strong><span class="code">driver_version</span></strong></dt>
<dd>
<p>Returns a string containing the erlang driver version
used by the runtime system. It will be on the form
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl_driver.html#version_management');">"<major ver>.<minor ver>"</a></span>.</p>
</dd>
<dt><strong><span class="code">dynamic_trace</span></strong></dt>
<dd>
<p>Returns an atom describing the dynamic trace framework
compiled into the virtual machine. It can currently be either
<span class="code">dtrace</span>, <span class="code">systemtap</span> or <span class="code">none</span>. For a
commercial or standard build, this is always <span class="code">none</span>,
the other return values indicate a custom configuration
(e.g. <span class="code">./configure --with-dynamic-trace=dtrace</span>). See
the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','runtime_tools','dyntrace.html');">dyntrace
</a></span> manual page and the
<span class="code">README.dtrace</span>/<span class="code">README.systemtap</span> files in the
Erlang source code top directory for more information
about dynamic tracing.</p>
</dd>
<dt><strong><span class="code">dynamic_trace_probes</span></strong></dt>
<dd>
<p>Returns a <span class="code">boolean()</span> indicating if dynamic trace probes
(either dtrace or systemtap) are built into the
emulator. This can only be <span class="code">true</span> if the virtual
machine was built for dynamic tracing
(i.e. <span class="code">system_info(dynamic_trace)</span> returns
<span class="code">dtrace</span> or <span class="code">systemtap</span>).</p>
</dd>
<dt><strong><span class="code">elib_malloc</span></strong></dt>
<dd>
<p>This option will be removed in a future release.
The return value will always be <span class="code">false</span> since
the elib_malloc allocator has been removed.</p>
</dd>
<dt><strong><a name="system_info_dist_buf_busy_limit"><span class="code">dist_buf_busy_limit</span></a></strong></dt>
<dd>
<p>Returns the value of the distribution buffer busy limit
in bytes. This limit can be set on startup by passing the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+zdbbl');">+zdbbl</a></span> command line
flag to <span class="code">erl</span>.</p>
</dd>
<dt><strong><span class="code">fullsweep_after</span></strong></dt>
<dd>
<p>Returns <span class="code">{fullsweep_after, integer()}</span> which is the
<span class="code">fullsweep_after</span> garbage collection setting used
by default. For more information see
<span class="code">garbage_collection</span> described below.</p>
</dd>
<dt><strong><span class="code">garbage_collection</span></strong></dt>
<dd>
<p>Returns a list describing the default garbage collection
settings. A process spawned on the local node by a
<span class="code">spawn</span> or <span class="code">spawn_link</span> will use these
garbage collection settings. The default settings can be
changed by use of
<span class="bold_code"><a href="#system_flag-2">system_flag/2</a></span>.
<span class="bold_code"><a href="#spawn_opt-4">spawn_opt/4</a></span>
can spawn a process that does not use the default
settings.</p>
</dd>
<dt><strong><span class="code">heap_sizes</span></strong></dt>
<dd>
<p>Returns a list of integers representing valid heap sizes
in words. All Erlang heaps are sized from sizes in this
list.</p>
</dd>
<dt><strong><span class="code">heap_type</span></strong></dt>
<dd>
<p>Returns the heap type used by the current emulator.
Currently only the following heap type exists:</p>
<dl>
<dt><strong><span class="code">private</span></strong></dt>
<dd>
<p>Each process has a heap reserved for its use and no
references between heaps of different processes are
allowed. Messages passed between processes are copied
between heaps.</p>
</dd>
</dl>
</dd>
<dt><strong><span class="code">info</span></strong></dt>
<dd>
<p>Returns a binary containing a string of miscellaneous
system information formatted as in Erlang crash dumps.
For more information see the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','crash_dump.html');">"How to interpret the Erlang crash dumps"</a></span> chapter in the ERTS
User's Guide.</p>
</dd>
<dt><strong><span class="code">kernel_poll</span></strong></dt>
<dd>
<p>Returns <span class="code">true</span> if the emulator uses some kind of
kernel-poll implementation; otherwise, <span class="code">false</span>.</p>
</dd>
<dt><strong><span class="code">loaded</span></strong></dt>
<dd>
<p>Returns a binary containing a string of loaded module
information formatted as in Erlang crash dumps. For more
information see the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','crash_dump.html');">"How to interpret the Erlang crash dumps"</a></span> chapter
in the ERTS User's Guide.</p>
</dd>
<dt><strong><a name="logical_processors"><span class="code">logical_processors</span></a></strong></dt>
<dd>
<p>Returns the detected number of logical processors configured
on the system. The return value is either an integer, or
the atom <span class="code">unknown</span> if the emulator wasn't able to
detect logical processors configured.
</p>
</dd>
<dt><strong><a name="logical_processors_available"><span class="code">logical_processors_available</span></a></strong></dt>
<dd>
<p>Returns the detected number of logical processors available to
the Erlang runtime system. The return value is either an
integer, or the atom <span class="code">unknown</span> if the emulator wasn't
able to detect logical processors available. The number
of logical processors available is less than or equal to
the number of <span class="bold_code"><a href="#logical_processors_online">logical
processors online</a></span>.
</p>
</dd>
<dt><strong><a name="logical_processors_online"><span class="code">logical_processors_online</span></a></strong></dt>
<dd>
<p>Returns the detected number of logical processors online on
the system. The return value is either an integer,
or the atom <span class="code">unknown</span> if the emulator wasn't able to
detect logical processors online. The number of logical
processors online is less than or equal to the number of
<span class="bold_code"><a href="#logical_processors">logical processors
configured</a></span>.
</p>
</dd>
<dt><strong><span class="code">machine</span></strong></dt>
<dd>
<p>Returns a string containing the Erlang machine name.</p>
</dd>
<dt><strong><span class="code">min_heap_size</span></strong></dt>
<dd>
<p>Returns <span class="code">{min_heap_size, MinHeapSize}</span> where <span class="code">MinHeapSize</span> is the current system wide
minimum heap size for spawned processes.</p>
</dd>
<dt><strong><span class="code">min_bin_vheap_size</span></strong></dt>
<dd>
<p>Returns <span class="code">{min_bin_vheap_size, MinBinVHeapSize}</span> where <span class="code">MinBinVHeapSize</span> is the current system wide
minimum binary virtual heap size for spawned processes.</p>
</dd>
<dt><strong><span class="code">modified_timing_level</span></strong></dt>
<dd>
<p>Returns the modified timing level (an integer) if
modified timing has been enabled; otherwise,
<span class="code">undefined</span>. See the <span class="code">+T</span> command line flag
in the documentation of the
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+T');">erl(1)</a></span>
command for more information on modified timing.</p>
</dd>
<dt><strong><a name="system_info_multi_scheduling"><span class="code">multi_scheduling</span></a></strong></dt>
<dd>
<p>Returns <span class="code">disabled</span>, <span class="code">blocked</span>, or <span class="code">enabled</span>.
A description of the return values:</p>
<dl>
<dt><strong><span class="code">disabled</span></strong></dt>
<dd>
<p>The emulator has only one scheduler thread. The
emulator does not have SMP support, or have been
started with only one scheduler thread.</p>
</dd>
<dt><strong><span class="code">blocked</span></strong></dt>
<dd>
<p>The emulator has more than one scheduler thread,
but all scheduler threads but one have been blocked,
i.e., only one scheduler thread will schedule
Erlang processes and execute Erlang code.</p>
</dd>
<dt><strong><span class="code">enabled</span></strong></dt>
<dd>
<p>The emulator has more than one scheduler thread,
and no scheduler threads have been blocked, i.e.,
all available scheduler threads will schedule
Erlang processes and execute Erlang code.</p>
</dd>
</dl>
<p>See also <span class="bold_code"><a href="#system_flag_multi_scheduling">erlang:system_flag(multi_scheduling, BlockState)</a></span>,
<span class="bold_code"><a href="#system_info_multi_scheduling_blockers">erlang:system_info(multi_scheduling_blockers)</a></span>, and
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span>.</p>
</dd>
<dt><strong><a name="system_info_multi_scheduling_blockers"><span class="code">multi_scheduling_blockers</span></a></strong></dt>
<dd>
<p>Returns a list of <span class="code">PID</span>s when multi-scheduling
is blocked; otherwise, the empty list. The <span class="code">PID</span>s
in the list is <span class="code">PID</span>s of the processes currently
blocking multi-scheduling. A <span class="code">PID</span> will only be
present once in the list, even if the corresponding
process has blocked multiple times.</p>
<p>See also <span class="bold_code"><a href="#system_flag_multi_scheduling">erlang:system_flag(multi_scheduling, BlockState)</a></span>,
<span class="bold_code"><a href="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</a></span>, and
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span>.</p>
</dd>
<dt><strong><a name="system_info_otp_release"><span class="code">otp_release</span></a></strong></dt>
<dd>
<p>Returns a string containing the OTP release number.</p>
</dd>
<dt><strong><span class="code">process_count</span></strong></dt>
<dd>
<p>Returns the number of processes currently existing at
the local node as an integer. The same value as
<span class="code">length(processes())</span> returns.</p>
</dd>
<dt><strong><span class="code">process_limit</span></strong></dt>
<dd>
<p>Returns the maximum number of concurrently existing
processes at the local node as an integer. This limit
can be configured at startup by using the command line
flag <span class="code">+P</span>, see
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#max_processes');">erl(1)</a></span>.</p>
</dd>
<dt><strong><span class="code">procs</span></strong></dt>
<dd>
<p>Returns a binary containing a string of process and port
information formatted as in Erlang crash dumps. For more
information see the <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','crash_dump.html');">"How to interpret the Erlang crash dumps"</a></span> chapter
in the ERTS User's Guide.</p>
</dd>
<dt><strong><a name="system_info_scheduler_bind_type"><span class="code">scheduler_bind_type</span></a></strong></dt>
<dd>
<p>Returns information on how user has requested
schedulers to be bound or not bound.</p>
<p><strong>NOTE:</strong> Even though user has requested
schedulers to be bound, they might have silently failed
to bind. In order to inspect actual scheduler bindings call
<span class="bold_code"><a href="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</a></span>.
</p>
<p>For more information, see
the <span class="code">erl</span> <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt</a></span>
command line argument, and
<span class="bold_code"><a href="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</a></span>.
</p>
</dd>
<dt><strong><a name="system_info_scheduler_bindings"><span class="code">scheduler_bindings</span></a></strong></dt>
<dd>
<p>Returns information on currently used scheduler
bindings.</p>
<p>A tuple of a size equal to
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span> is returned. The elements of the tuple are integers
or the atom <span class="code">unbound</span>. Logical processor identifiers
are represented as integers. The <span class="code">N</span>th
element of the tuple equals the current binding for
the scheduler with the scheduler identifier equal to
<span class="code">N</span>. E.g., if the schedulers have been bound,
<span class="code">element(erlang:system_info(scheduler_id),
erlang:system_info(scheduler_bindings))</span> will return
the identifier of the logical processor that the calling
process is executing on.
</p>
<p>Note that only schedulers online can be bound to logical
processors.</p>
<p>For more information, see
the <span class="code">erl</span> <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl.html#+sbt');">+sbt</a></span>
command line argument,
<span class="bold_code"><a href="#system_info_schedulers_online">erlang:system_info(schedulers_online)</a></span>.
</p>
</dd>
<dt><strong><a name="system_info_scheduler_id"><span class="code">scheduler_id</span></a></strong></dt>
<dd>
<p>Returns the scheduler id (<span class="code">SchedulerId</span>) of the
scheduler thread that the calling process is executing
on. <span class="code">SchedulerId</span> is a positive integer; where
<span class="code">1 <= SchedulerId <= erlang:system_info(schedulers)</span>. See also
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span>.</p>
</dd>
<dt><strong><a name="system_info_schedulers"><span class="code">schedulers</span></a></strong></dt>
<dd>
<p>Returns the number of scheduler threads used by
the emulator. Scheduler threads online schedules Erlang
processes and Erlang ports, and execute Erlang code
and Erlang linked in driver code.</p>
<p>The number of scheduler threads is determined at
emulator boot time and cannot be changed after
that. The amount of schedulers online can
however be changed at any time.</p>
<p>See also <span class="bold_code"><a href="#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</a></span>,
<span class="bold_code"><a href="#system_info_schedulers_online">erlang:system_info(schedulers_online)</a></span>,
<span class="bold_code"><a href="#system_info_scheduler_id">erlang:system_info(scheduler_id)</a></span>,
<span class="bold_code"><a href="#system_flag_multi_scheduling">erlang:system_flag(multi_scheduling, BlockState)</a></span>,
<span class="bold_code"><a href="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</a></span>, and
and <span class="bold_code"><a href="#system_info_multi_scheduling_blockers">erlang:system_info(multi_scheduling_blockers)</a></span>.</p>
</dd>
<dt><strong><a name="system_info_schedulers_online"><span class="code">schedulers_online</span></a></strong></dt>
<dd>
<p>Returns the amount of schedulers online. The scheduler
identifiers of schedulers online satisfy the following
relationship:
<span class="code">1 <= SchedulerId <= erlang:system_info(schedulers_online)</span>.
</p>
<p>For more information, see
<span class="bold_code"><a href="#system_info_schedulers">erlang:system_info(schedulers)</a></span>,
and
<span class="bold_code"><a href="#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</a></span>.
</p>
</dd>
<dt><strong><span class="code">smp_support</span></strong></dt>
<dd>
<p>Returns <span class="code">true</span> if the emulator has been compiled
with smp support; otherwise, <span class="code">false</span>.</p>
</dd>
<dt><strong><span class="code">system_version</span></strong></dt>
<dd>
<p>Returns a string containing version number and
some important properties such as the number of schedulers.</p>
</dd>
<dt><strong><span class="code">system_architecture</span></strong></dt>
<dd>
<p>Returns a string containing the processor and OS
architecture the emulator is built for.</p>
</dd>
<dt><strong><span class="code">threads</span></strong></dt>
<dd>
<p>Returns <span class="code">true</span> if the emulator has been compiled
with thread support; otherwise, <span class="code">false</span> is
returned.</p>
</dd>
<dt><strong><a name="system_info_thread_pool_size"><span class="code">thread_pool_size</span></a></strong></dt>
<dd>
<p>Returns the number of async threads in the async thread
pool used for asynchronous driver calls
(<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','erl_driver.html#driver_async');">driver_async()</a></span>)
as an integer.</p>
</dd>
<dt><strong><span class="code">trace_control_word</span></strong></dt>
<dd>
<p>Returns the value of the node's trace control word.
For more information see documentation of the function
<span class="code">get_tcw</span> in "Match Specifications in Erlang",
<span class="bold_code"><a href="javascript:erlhref('../../../doc/../','erts','match_spec.html#get_tcw');">ERTS User's Guide</a></span>.</p>
</dd>
<dt><strong><a name="update_cpu_info"><span class="code">update_cpu_info</span></a></strong></dt>
<dd>
<p>The runtime system rereads the CPU information available and
updates its internally stored information about the
<span class="bold_code"><a href="#system_info_cpu_topology_detected">detected CPU
topology</a></span> and the amount of logical processors
<span class="bold_code"><a href="#logical_processors">configured</a></span>,
<span class="bold_code"><a href="#logical_processors_online">online</a></span>, and
<span class="bold_code"><a href="#logical_processors_available">available</a></span>.
If the CPU information has changed since the last time it was read,
the atom <span class="code">changed</span> is returned; otherwise, the atom
<span class="code">unchanged</span> is returned. If the CPU information has changed
you probably want to
<span class="bold_code"><a href="#system_flag_schedulers_online">adjust the amount
of schedulers online</a></span>. You typically want to have as
many schedulers online as
<span class="bold_code"><a href="#logical_processors_available">logical processors
available</a></span>.
</p>
</dd>
<dt><strong><a name="system_info_version"><span class="code">version</span></a></strong></dt>
<dd>
<p>Returns a string containing the version number of the
emulator.</p>
</dd>
<dt><strong><span class="code">wordsize</span></strong></dt>
<dd>
<p>Same as <span class="code">{wordsize, internal}.</span></p>
</dd>
<dt><strong><span class="code">{wordsize, internal}</span></strong></dt>
<dd>
<p>Returns the size of Erlang term words in bytes as an
integer, i.e. on a 32-bit architecture 4 is returned,
and on a pure 64-bit architecture 8 is returned. On a
halfword 64-bit emulator, 4 is returned, as the Erlang
terms are stored using a virtual wordsize of half the
system's wordsize.</p>
</dd>
<dt><strong><span class="code">{wordsize, external}</span></strong></dt>
<dd>
<p>Returns the true wordsize of the emulator, i.e. the size
of a pointer, in bytes as an integer. On a pure 32-bit
architecture 4 is returned, on both a halfword and pure
64-bit architecture, 8 is returned.</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The <span class="code">scheduler</span> argument has changed name to
<span class="code">scheduler_id</span>. This in order to avoid mixup with
the <span class="code">schedulers</span> argument. The <span class="code">scheduler</span>
argument was introduced in ERTS version 5.5 and renamed
in ERTS version 5.5.1.</p>
</p></div>
</div>
</p></div>
<p><a name="system_monitor-0"><span class="bold_code">erlang:system_monitor() -> MonSettings</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">MonSettings -> {MonitorPid, Options} | undefined</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> MonitorPid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Options = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Time = Size = integer()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the current system monitoring settings set by
<span class="bold_code"><a href="#system_monitor-2">erlang:system_monitor/2</a></span>
as <span class="code">{MonitorPid, Options}</span>, or <span class="code">undefined</span> if there
are no settings. The order of the options may be different
from the one that was set.</p>
</p></div>
<p><a name="system_monitor-1"><span class="bold_code">erlang:system_monitor(undefined | {MonitorPid, Options}) -> MonSettings</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">MonitorPid, Options, MonSettings -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>When called with the argument <span class="code">undefined</span>, all
system performance monitoring settings are cleared.</p>
<p>Calling the function with <span class="code">{MonitorPid, Options}</span> as
argument, is the same as calling
<span class="bold_code"><a href="#system_monitor-2">erlang:system_monitor(MonitorPid, Options)</a></span>.</p>
<p>Returns the previous system monitor settings just like
<span class="bold_code"><a href="#system_monitor-0">erlang:system_monitor/0</a></span>.</p>
</p></div>
<p><a name="system_monitor-2"><span class="bold_code">erlang:system_monitor(MonitorPid, [Option]) -> MonSettings</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">MonitorPid = pid()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Time = Size = integer()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">MonSettings = {OldMonitorPid, [Option]}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> OldMonitorPid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets system performance monitoring options. <span class="code">MonitorPid</span>
is a local pid that will receive system monitor messages, and
the second argument is a list of monitoring options:</p>
<dl>
<dt><strong><span class="code">{long_gc, Time}</span></strong></dt>
<dd>
<p>If a garbage collection in the system takes at least
<span class="code">Time</span> wallclock milliseconds, a message
<span class="code">{monitor, GcPid, long_gc, Info}</span> is sent to
<span class="code">MonitorPid</span>. <span class="code">GcPid</span> is the pid that was
garbage collected and <span class="code">Info</span> is a list of two-element
tuples describing the result of the garbage collection.
One of the tuples is <span class="code">{timeout, GcTime}</span> where
<span class="code">GcTime</span> is the actual time for the garbage
collection in milliseconds. The other tuples are
tagged with <span class="code">heap_size</span>, <span class="code">heap_block_size</span>,
<span class="code">stack_size</span>, <span class="code">mbuf_size</span>, <span class="code">old_heap_size</span>,
and <span class="code">old_heap_block_size</span>. These tuples are
explained in the documentation of the
<span class="bold_code"><a href="#gc_start">gc_start</a></span>
trace message (see
<span class="bold_code"><a href="#trace-3">erlang:trace/3</a></span>).
New tuples may be added, and the order of the tuples in
the <span class="code">Info</span> list may be changed at any time without prior
notice.
</p>
</dd>
<dt><strong><span class="code">{large_heap, Size}</span></strong></dt>
<dd>
<p>If a garbage collection in the system results in
the allocated size of a heap being at least <span class="code">Size</span>
words, a message <span class="code">{monitor, GcPid, large_heap, Info}</span>
is sent to <span class="code">MonitorPid</span>. <span class="code">GcPid</span> and <span class="code">Info</span>
are the same as for <span class="code">long_gc</span> above, except that
the tuple tagged with <span class="code">timeout</span> is not present.
<strong>Note</strong>: As of erts version 5.6 the monitor message
is sent if the sum of the sizes of all memory blocks allocated
for all heap generations is equal to or larger than <span class="code">Size</span>.
Previously the monitor message was sent if the memory block
allocated for the youngest generation was equal to or larger
than <span class="code">Size</span>.
</p>
</dd>
<dt><strong><span class="code">busy_port</span></strong></dt>
<dd>
<p>If a process in the system gets suspended because it
sends to a busy port, a message
<span class="code">{monitor, SusPid, busy_port, Port}</span> is sent to
<span class="code">MonitorPid</span>. <span class="code">SusPid</span> is the pid that got
suspended when sending to <span class="code">Port</span>.</p>
</dd>
<dt><strong><span class="code">busy_dist_port</span></strong></dt>
<dd>
<p>If a process in the system gets suspended because it
sends to a process on a remote node whose inter-node
communication was handled by a busy port, a message
<span class="code">{monitor, SusPid, busy_dist_port, Port}</span> is sent to
<span class="code">MonitorPid</span>. <span class="code">SusPid</span> is the pid that got
suspended when sending through the inter-node
communication port <span class="code">Port</span>.</p>
</dd>
</dl>
<p>Returns the previous system monitor settings just like
<span class="bold_code"><a href="#system_monitor-0">erlang:system_monitor/0</a></span>.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>If a monitoring process gets so large that it itself
starts to cause system monitor messages when garbage
collecting, the messages will enlarge the process's
message queue and probably make the problem worse.</p>
<p>Keep the monitoring process neat and do not set the system
monitor limits too tight.</p>
</p></div>
</div>
<p>Failure: <span class="code">badarg</span> if <span class="code">MonitorPid</span> does not exist.</p>
</p></div>
<p><a name="system_profile-0"><span class="bold_code">erlang:system_profile() -> ProfilerSettings</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">ProfilerSettings -> {ProfilerPid, Options} | undefined</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> ProfilerPid = pid() | port()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Options = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Option = runnable_procs | runnable_ports | scheduler | exclusive</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the current system profiling settings set by
<span class="bold_code"><a href="#system_profile-2">erlang:system_profile/2</a></span>
as <span class="code">{ProfilerPid, Options}</span>, or <span class="code">undefined</span> if there
are no settings. The order of the options may be different
from the one that was set.</p>
</p></div>
<p><a name="system_profile-2"><span class="bold_code">erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">ProfilerSettings -> {ProfilerPid, Options} | undefined</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> ProfilerPid = pid() | port()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Options = [Option]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Option = runnable_procs | runnable_ports | scheduler | exclusive</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets system profiler options. <span class="code">ProfilerPid</span>
is a local pid or port that will receive profiling messages. The
receiver is excluded from all profiling.
The second argument is a list of profiling options:</p>
<dl>
<dt><strong><span class="code">runnable_procs</span></strong></dt>
<dd>
<p>If a process is put into or removed from the run queue a message,
<span class="code">{profile, Pid, State, Mfa, Ts}</span>, is sent to
<span class="code">ProfilerPid</span>. Running processes that is reinserted into the
run queue after having been preemptively scheduled out will not trigger this
message.
</p>
</dd>
<dt><strong><span class="code">runnable_ports</span></strong></dt>
<dd>
<p>If a port is put into or removed from the run queue a message,
<span class="code">{profile, Port, State, 0, Ts}</span>, is sent to
<span class="code">ProfilerPid</span>.
</p>
</dd>
<dt><strong><span class="code">scheduler</span></strong></dt>
<dd>
<p>If a scheduler is put to sleep or awoken a message,
<span class="code">{profile, scheduler, Id, State, NoScheds, Ts}</span>, is sent
to <span class="code">ProfilerPid</span>.
</p>
</dd>
<dt><strong><span class="code">exclusive</span></strong></dt>
<dd>
<p>
If a synchronous call to a port from a process is done, the
calling process is considered not runnable during the call
runtime to the port. The calling process is notified as
<span class="code">inactive</span> and subsequently <span class="code">active</span> when the port
callback returns.
</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p><p><span class="code">erlang:system_profile</span> is considered experimental and
its behaviour may change in the future.</p>
</p></div>
</div>
</p></div>
<p><a name="term_to_binary-1"><span class="bold_code">term_to_binary(Term) -> ext_binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a binary data object which is the result of encoding
<span class="code">Term</span> according to the Erlang external term format.</p>
<p>This can be used for a variety of purposes, for example
writing a term to a file in an efficient way, or sending an
Erlang term to some type of communications channel not
supported by distributed Erlang.</p>
<p>See also
<span class="bold_code"><a href="#binary_to_term-1">binary_to_term/1</a></span>.</p>
</p></div>
<p><a name="term_to_binary-2"><span class="bold_code">term_to_binary(Term, [Option]) -> ext_binary()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Term = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Option = compressed | {compressed,Level} | {minor_version,Version}</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a binary data object which is the result of encoding
<span class="code">Term</span> according to the Erlang external term format.</p>
<p>If the option <span class="code">compressed</span> is provided, the external
term format will be compressed. The compressed format is
automatically recognized by <span class="code">binary_to_term/1</span> in R7B and later.</p>
<p>It is also possible to specify a compression level by giving
the option <span class="code">{compressed,Level}</span>, where <span class="code">Level</span> is an
integer from 0 through 9. <span class="code">0</span> means that no compression
will be done (it is the same as not giving any <span class="code">compressed</span> option);
<span class="code">1</span> will take the least time but may not compress as well as
the higher levels; <span class="code">9</span> will take the most time and may produce
a smaller result. Note the "mays" in the preceding sentence; depending
on the input term, level 9 compression may or may not produce a smaller
result than level 1 compression.</p>
<p>Currently, <span class="code">compressed</span> gives the same result as
<span class="code">{compressed,6}</span>.</p>
<p>The option <span class="code">{minor_version,Version}</span> can be use to control
some details of the encoding. This option was
introduced in R11B-4. Currently, the allowed values for <span class="code">Version</span>
are <span class="code">0</span> and <span class="code">1</span>.</p>
<p><span class="code">{minor_version,1}</span> forces any floats in the term to be encoded
in a more space-efficient and exact way (namely in the 64-bit IEEE format,
rather than converted to a textual representation). <span class="code">binary_to_term/1</span>
in R11B-4 and later is able decode the new representation.</p>
<p><span class="code">{minor_version,0}</span> is currently the default, meaning that floats
will be encoded using a textual representation; this option is useful if
you want to ensure that releases prior to R11B-4 can decode resulting
binary.</p>
<p>See also
<span class="bold_code"><a href="#binary_to_term-1">binary_to_term/1</a></span>.</p>
</p></div>
<p><a name="throw-1"><span class="bold_code">throw(Any)</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Any = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>A non-local return from a function. If evaluated within a
<span class="code">catch</span>, <span class="code">catch</span> will return the value <span class="code">Any</span>.</p>
<div class="example"><pre>
> <span class="bold_code">catch throw({hello, there}).</span>
{hello,there}</pre></div>
<p>Failure: <span class="code">nocatch</span> if not evaluated within a catch.</p>
</p></div>
<p><a name="time-0"><span class="bold_code">time() -> {Hour, Minute, Second}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Hour = Minute = Second = integer() >= 0</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the current time as <span class="code">{Hour, Minute, Second}</span>.</p>
<p>The time zone and daylight saving time correction depend on
the underlying OS.</p>
<div class="example"><pre>
> <span class="bold_code">time().</span>
{9,42,44}</pre></div>
</p></div>
<p><a name="tl-1"><span class="bold_code">tl(List1) -> List2</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">List1 = List2 = [term()]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the tail of <span class="code">List1</span>, that is, the list minus
the first element.</p>
<div class="example"><pre>
> <span class="bold_code">tl([geesties, guilies, beasties]).</span>
[guilies, beasties]</pre></div>
<p>Allowed in guard tests.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">List</span> is the empty list [].</p>
</p></div>
<p><a name="trace-3"><span class="bold_code">erlang:trace(PidSpec, How, FlagList) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">PidSpec = pid() | existing | new | all</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">How = boolean()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FlagList = [Flag]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Flag -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Turns on (if <span class="code">How == true</span>) or off (if
<span class="code">How == false</span>) the trace flags in <span class="code">FlagList</span> for
the process or processes represented by <span class="code">PidSpec</span>.</p>
<p><span class="code">PidSpec</span> is either a pid for a local process, or one of
the following atoms:</p>
<dl>
<dt><strong><span class="code">existing</span></strong></dt>
<dd>
<p>All processes currently existing.</p>
</dd>
<dt><strong><span class="code">new</span></strong></dt>
<dd>
<p>All processes that will be created in the future.</p>
</dd>
<dt><strong><span class="code">all</span></strong></dt>
<dd>
<p>All currently existing processes and all processes that
will be created in the future.</p>
</dd>
</dl>
<p><span class="code">FlagList</span> can contain any number of the following
flags (the "message tags" refers to the list of messages
following below):</p>
<dl>
<dt><strong><span class="code">all</span></strong></dt>
<dd>
<p>Set all trace flags except <span class="code">{tracer, Tracer}</span> and
<span class="code">cpu_timestamp</span> that are in their nature different
than the others.</p>
</dd>
<dt><strong><span class="code">send</span></strong></dt>
<dd>
<p>Trace sending of messages.</p>
<p>Message tags: <span class="code">send</span>,
<span class="code">send_to_non_existing_process</span>.</p>
</dd>
<dt><strong><span class="code">'receive'</span></strong></dt>
<dd>
<p>Trace receiving of messages.</p>
<p>Message tags: <span class="code">'receive'</span>.</p>
</dd>
<dt><strong><span class="code">procs</span></strong></dt>
<dd>
<p>Trace process related events.</p>
<p>Message tags: <span class="code">spawn</span>, <span class="code">exit</span>,
<span class="code">register</span>, <span class="code">unregister</span>, <span class="code">link</span>,
<span class="code">unlink</span>, <span class="code">getting_linked</span>,
<span class="code">getting_unlinked</span>.</p>
</dd>
<dt><strong><span class="code">call</span></strong></dt>
<dd>
<p>Trace certain function calls. Specify which function
calls to trace by calling
<span class="bold_code"><a href="#trace_pattern-3">erlang:trace_pattern/3</a></span>.</p>
<p>Message tags: <span class="code">call</span>, <span class="code">return_from</span>.</p>
</dd>
<dt><strong><span class="code">silent</span></strong></dt>
<dd>
<p>Used in conjunction with the <span class="code">call</span> trace flag.
The <span class="code">call</span>, <span class="code">return_from</span> and <span class="code">return_to</span>
trace messages are inhibited if this flag is set,
but if there are match specs they are executed as normal.</p>
<p>Silent mode is inhibited by executing
<span class="code">erlang:trace(_, false, [silent|_])</span>,
or by a match spec executing the <span class="code">{silent, false}</span>
function.</p>
<p>The <span class="code">silent</span> trace flag facilitates setting up
a trace on many or even all processes in the system.
Then the interesting trace can be activated and
deactivated using the <span class="code">{silent,Bool}</span>
match spec function, giving a high degree
of control of which functions with which
arguments that triggers the trace.</p>
<p>Message tags: <span class="code">call</span>, <span class="code">return_from</span>,
<span class="code">return_to</span>. Or rather, the absence of.</p>
</dd>
<dt><strong><span class="code">return_to</span></strong></dt>
<dd>
<p>Used in conjunction with the <span class="code">call</span> trace flag.
Trace the actual return from a traced function back to
its caller. Only works for functions traced with
the <span class="code">local</span> option to
<span class="bold_code"><a href="#trace_pattern-3">erlang:trace_pattern/3</a></span>.</p>
<p>The semantics is that a trace message is sent when a
call traced function actually returns, that is, when a
chain of tail recursive calls is ended. There will be
only one trace message sent per chain of tail recursive
calls, why the properties of tail recursiveness for
function calls are kept while tracing with this flag.
Using <span class="code">call</span> and <span class="code">return_to</span> trace together
makes it possible to know exactly in which function a
process executes at any time.</p>
<p>To get trace messages containing return values from
functions, use the <span class="code">{return_trace}</span> match_spec
action instead.</p>
<p>Message tags: <span class="code">return_to</span>.</p>
</dd>
<dt><strong><span class="code">running</span></strong></dt>
<dd>
<p>Trace scheduling of processes.</p>
<p>Message tags: <span class="code">in</span>, and <span class="code">out</span>.</p>
</dd>
<dt><strong><span class="code">exiting</span></strong></dt>
<dd>
<p>Trace scheduling of an exiting processes.</p>
<p>Message tags: <span class="code">in_exiting</span>, <span class="code">out_exiting</span>, and
<span class="code">out_exited</span>.</p>
</dd>
<dt><strong><span class="code">garbage_collection</span></strong></dt>
<dd>
<p>Trace garbage collections of processes.</p>
<p>Message tags: <span class="code">gc_start</span>, <span class="code">gc_end</span>.</p>
</dd>
<dt><strong><span class="code">timestamp</span></strong></dt>
<dd>
<p>Include a time stamp in all trace messages. The time
stamp (Ts) is of the same form as returned by
<span class="code">erlang:now()</span>.</p>
</dd>
<dt><strong><span class="code">cpu_timestamp</span></strong></dt>
<dd>
<p>A global trace flag for the Erlang node that makes all
trace timestamps be in CPU time, not wallclock. It is
only allowed with <span class="code">PidSpec==all</span>. If the host
machine operating system does not support high resolution
CPU time measurements, <span class="code">trace/3</span> exits with
<span class="code">badarg</span>.</p>
</dd>
<dt><strong><span class="code">arity</span></strong></dt>
<dd>
<p>Used in conjunction with the <span class="code">call</span> trace flag.
<span class="code">{M, F, Arity}</span> will be specified instead of
<span class="code">{M, F, Args}</span> in call trace messages.</p>
</dd>
<dt><strong><span class="code">set_on_spawn</span></strong></dt>
<dd>
<p>Makes any process created by a traced process inherit
its trace flags, including the <span class="code">set_on_spawn</span> flag.</p>
</dd>
<dt><strong><span class="code">set_on_first_spawn</span></strong></dt>
<dd>
<p>Makes the first process created by a traced process
inherit its trace flags, excluding
the <span class="code">set_on_first_spawn</span> flag.</p>
</dd>
<dt><strong><span class="code">set_on_link</span></strong></dt>
<dd>
<p>Makes any process linked by a traced process inherit its
trace flags, including the <span class="code">set_on_link</span> flag.</p>
</dd>
<dt><strong><span class="code">set_on_first_link</span></strong></dt>
<dd>
<p>Makes the first process linked to by a traced process
inherit its trace flags, excluding
the <span class="code">set_on_first_link</span> flag.</p>
</dd>
<dt><strong><span class="code">{tracer, Tracer}</span></strong></dt>
<dd>
<p>Specify where to send the trace messages. <span class="code">Tracer</span>
must be the pid of a local process or the port identifier
of a local port. If this flag is not given, trace
messages will be sent to the process that called
<span class="code">erlang:trace/3</span>.</p>
</dd>
</dl>
<p>The effect of combining <span class="code">set_on_first_link</span> with
<span class="code">set_on_link</span> is the same as having
<span class="code">set_on_first_link</span> alone. Likewise for
<span class="code">set_on_spawn</span> and <span class="code">set_on_first_spawn</span>.</p>
<p>If the <span class="code">timestamp</span> flag is not given, the tracing
process will receive the trace messages described below.
<span class="code">Pid</span> is the pid of the traced process in which
the traced event has occurred. The third element of the tuple
is the message tag.</p>
<p>If the <span class="code">timestamp</span> flag is given, the first element of
the tuple will be <span class="code">trace_ts</span> instead and the timestamp
is added last in the tuple.</p>
<dl>
<dt><strong><span class="code">{trace, Pid, 'receive', Msg}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> receives the message <span class="code">Msg</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, send, Msg, To}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> sends the message <span class="code">Msg</span> to
the process <span class="code">To</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, send_to_non_existing_process, Msg, To}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> sends the message <span class="code">Msg</span> to
the non-existing process <span class="code">To</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, call, {M, F, Args}}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> calls a traced function. The return
values of calls are never supplied, only the call and its
arguments.</p>
<p>Note that the trace flag <span class="code">arity</span> can be used to
change the contents of this message, so that <span class="code">Arity</span>
is specified instead of <span class="code">Args</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, return_to, {M, F, Arity}}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> returns <strong>to</strong> the specified
function. This trace message is sent if both
the <span class="code">call</span> and the <span class="code">return_to</span> flags are set,
and the function is set to be traced on <strong>local</strong>
function calls. The message is only sent when returning
from a chain of tail recursive function calls where at
least one call generated a <span class="code">call</span> trace message
(that is, the functions match specification matched and
<span class="code">{message, false}</span> was not an action).</p>
</dd>
<dt><strong><span class="code">{trace, Pid, return_from, {M, F, Arity}, ReturnValue}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> returns <strong>from</strong> the specified
function. This trace message is sent if the <span class="code">call</span>
flag is set, and the function has a match specification
with a <span class="code">return_trace</span> or <span class="code">exception_trace</span> action.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> exits <strong>from</strong> the specified
function due to an exception. This trace message is sent
if the <span class="code">call</span> flag is set, and the function has
a match specification with an <span class="code">exception_trace</span> action.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, spawn, Pid2, {M, F, Args}}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> spawns a new process <span class="code">Pid2</span> with
the specified function call as entry point.</p>
<p>Note that <span class="code">Args</span> is supposed to be the argument
list, but may be any term in the case of an erroneous
spawn.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, exit, Reason}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> exits with reason <span class="code">Reason</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, link, Pid2}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> links to a process <span class="code">Pid2</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, unlink, Pid2}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> removes the link from a process
<span class="code">Pid2</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, getting_linked, Pid2}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> gets linked to a process <span class="code">Pid2</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, getting_unlinked, Pid2}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> gets unlinked from a process <span class="code">Pid2</span>.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, register, RegName}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> gets the name <span class="code">RegName</span> registered.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, unregister, RegName}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> gets the name <span class="code">RegName</span> unregistered.
Note that this is done automatically when a registered
process exits.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, in, {M, F, Arity} | 0}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> is scheduled to run. The process will
run in function <span class="code">{M, F, Arity}</span>. On some rare
occasions the current function cannot be determined, then
the last element <span class="code">Arity</span> is 0.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, out, {M, F, Arity} | 0}</span></strong></dt>
<dd>
<p>When <span class="code">Pid</span> is scheduled out. The process was
running in function {M, F, Arity}. On some rare occasions
the current function cannot be determined, then the last
element <span class="code">Arity</span> is 0.</p>
</dd>
<dt><strong><a name="gc_start"><span class="code">{trace, Pid, gc_start, Info}</span></a></strong></dt>
<dd>
<p>Sent when garbage collection is about to be started.
<span class="code">Info</span> is a list of two-element tuples, where
the first element is a key, and the second is the value.
You should not depend on the tuples have any defined
order. Currently, the following keys are defined:</p>
<dl>
<dt><strong><span class="code">heap_size</span></strong></dt>
<dd>The size of the used part of the heap.</dd>
<dt><strong><span class="code">heap_block_size</span></strong></dt>
<dd>The size of the memory block used for storing
the heap and the stack.</dd>
<dt><strong><span class="code">old_heap_size</span></strong></dt>
<dd>The size of the used part of the old heap.</dd>
<dt><strong><span class="code">old_heap_block_size</span></strong></dt>
<dd>The size of the memory block used for storing
the old heap.</dd>
<dt><strong><span class="code">stack_size</span></strong></dt>
<dd>The actual size of the stack.</dd>
<dt><strong><span class="code">recent_size</span></strong></dt>
<dd>The size of the data that survived the previous garbage
collection.</dd>
<dt><strong><span class="code">mbuf_size</span></strong></dt>
<dd>The combined size of message buffers associated with
the process.</dd>
<dt><strong><span class="code">bin_vheap_size</span></strong></dt>
<dd>The total size of unique off-heap binaries referenced from the process heap.</dd>
<dt><strong><span class="code">bin_vheap_block_size</span></strong></dt>
<dd>The total size of binaries, in words, allowed in the virtual
heap in the process before doing a garbage collection. </dd>
<dt><strong><span class="code">bin_old_vheap_size</span></strong></dt>
<dd>The total size of unique off-heap binaries referenced from the process old heap.</dd>
<dt><strong><span class="code">bin_vheap_block_size</span></strong></dt>
<dd>The total size of binaries, in words, allowed in the virtual
old heap in the process before doing a garbage collection. </dd>
</dl>
<p>All sizes are in words.</p>
</dd>
<dt><strong><span class="code">{trace, Pid, gc_end, Info}</span></strong></dt>
<dd>
<p>Sent when garbage collection is finished. <span class="code">Info</span>
contains the same kind of list as in the <span class="code">gc_start</span>
message, but the sizes reflect the new sizes after
garbage collection.</p>
</dd>
</dl>
<p>If the tracing process dies, the flags will be silently
removed.</p>
<p>Only one process can trace a particular process. For this
reason, attempts to trace an already traced process will fail.</p>
<p>Returns: A number indicating the number of processes that
matched <span class="code">PidSpec</span>. If <span class="code">PidSpec</span> is a pid,
the return value will be <span class="code">1</span>. If <span class="code">PidSpec</span> is
<span class="code">all</span> or <span class="code">existing</span> the return value will be
the number of processes running, excluding tracer processes.
If <span class="code">PidSpec</span> is <span class="code">new</span>, the return value will be
<span class="code">0</span>.</p>
<p>Failure: If specified arguments are not supported. For
example <span class="code">cpu_timestamp</span> is not supported on all
platforms.</p>
</p></div>
<p><a name="trace_delivered-1"><span class="bold_code">erlang:trace_delivered(Tracee) -> Ref</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Tracee = pid() | all</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Ref = reference()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The delivery of trace messages is dislocated on the time-line
compared to other events in the system. If you know that the
<span class="code">Tracee</span> has passed some specific point in its execution,
and you want to know when at least all trace messages
corresponding to events up to this point have reached the tracer
you can use <span class="code">erlang:trace_delivered(Tracee)</span>. A
<span class="code">{trace_delivered, Tracee, Ref}</span> message is sent to
the caller of <span class="code">erlang:trace_delivered(Tracee)</span> when it
is guaranteed that all trace messages have been delivered to
the tracer up to the point that the <span class="code">Tracee</span> had reached
at the time of the call to
<span class="code">erlang:trace_delivered(Tracee)</span>.</p>
<p>Note that the <span class="code">trace_delivered</span> message does <strong>not</strong>
imply that trace messages have been delivered; instead, it implies
that all trace messages that <strong>should</strong> be delivered have
been delivered. It is not an error if <span class="code">Tracee</span> isn't, and
hasn't been traced by someone, but if this is the case,
<strong>no</strong> trace messages will have been delivered when the
<span class="code">trace_delivered</span> message arrives.</p>
<p>Note that <span class="code">Tracee</span> has to refer to a process currently,
or previously existing on the same node as the caller of
<span class="code">erlang:trace_delivered(Tracee)</span> resides on.
The special <span class="code">Tracee</span> atom <span class="code">all</span> denotes all processes
that currently are traced in the node.</p>
<p>An example: Process <span class="code">A</span> is tracee, port <span class="code">B</span> is
tracer, and process <span class="code">C</span> is the port owner of <span class="code">B</span>.
<span class="code">C</span> wants to close <span class="code">B</span> when <span class="code">A</span> exits. <span class="code">C</span>
can ensure that the trace isn't truncated by calling
<span class="code">erlang:trace_delivered(A)</span> when <span class="code">A</span> exits and wait
for the <span class="code">{trace_delivered, A, Ref}</span> message before closing
<span class="code">B</span>.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">Tracee</span> does not refer to a
process (dead or alive) on the same node as the caller of
<span class="code">erlang:trace_delivered(Tracee)</span> resides on.</p>
</p></div>
<p><a name="trace_info-2"><span class="bold_code">erlang:trace_info(PidOrFunc, Item) -> Res</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">PidOrFunc = pid() | new | {Module, Function, Arity} | on_load</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Module = Function = atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Arity = arity()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Item, Res -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns trace information about a process or function.</p>
<p>To get information about a process, <span class="code">PidOrFunc</span> should
be a pid or the atom <span class="code">new</span>. The atom <span class="code">new</span> means
that the default trace state for processes to be created will
be returned. <span class="code">Item</span> must have one of the following
values:</p>
<dl>
<dt><strong><span class="code">flags</span></strong></dt>
<dd>
<p>Return a list of atoms indicating what kind of traces is
enabled for the process. The list will be empty if no
traces are enabled, and one or more of the followings
atoms if traces are enabled: <span class="code">send</span>,
<span class="code">'receive'</span>, <span class="code">set_on_spawn</span>, <span class="code">call</span>,
<span class="code">return_to</span>, <span class="code">procs</span>, <span class="code">set_on_first_spawn</span>,
<span class="code">set_on_link</span>, <span class="code">running</span>,
<span class="code">garbage_collection</span>, <span class="code">timestamp</span>, and
<span class="code">arity</span>. The order is arbitrary.</p>
</dd>
<dt><strong><span class="code">tracer</span></strong></dt>
<dd>
<p>Return the identifier for process or port tracing this
process. If this process is not being traced, the return
value will be <span class="code">[]</span>.</p>
</dd>
</dl>
<p>To get information about a function, <span class="code">PidOrFunc</span> should
be a three-element tuple: <span class="code">{Module, Function, Arity}</span> or
the atom <span class="code">on_load</span>. No wildcards are allowed. Returns
<span class="code">undefined</span> if the function does not exist or
<span class="code">false</span> if the function is not traced at all. <span class="code">Item</span>
must have one of the following values:</p>
<dl>
<dt><strong><span class="code">traced</span></strong></dt>
<dd>
<p>Return <span class="code">global</span> if this function is traced on
global function calls, <span class="code">local</span> if this function is
traced on local function calls (i.e local and global
function calls), and <span class="code">false</span> if neither local nor
global function calls are traced.</p>
</dd>
<dt><strong><span class="code">match_spec</span></strong></dt>
<dd>
<p>Return the match specification for this function, if it
has one. If the function is locally or globally traced but
has no match specification defined, the returned value
is <span class="code">[]</span>.</p>
</dd>
<dt><strong><span class="code">meta</span></strong></dt>
<dd>
<p>Return the meta trace tracer process or port for this
function, if it has one. If the function is not meta
traced the returned value is <span class="code">false</span>, and if
the function is meta traced but has once detected that
the tracer proc is invalid, the returned value is [].</p>
</dd>
<dt><strong><span class="code">meta_match_spec</span></strong></dt>
<dd>
<p>Return the meta trace match specification for this
function, if it has one. If the function is meta traced
but has no match specification defined, the returned
value is <span class="code">[]</span>.</p>
</dd>
<dt><strong><span class="code">call_count</span></strong></dt>
<dd>
<p>Return the call count value for this function or
<span class="code">true</span> for the pseudo function <span class="code">on_load</span> if call
count tracing is active. Return <span class="code">false</span> otherwise.
See also
<span class="bold_code"><a href="#trace_pattern-3">erlang:trace_pattern/3</a></span>.</p>
</dd>
<dt><strong><span class="code">call_time</span></strong></dt>
<dd>
<p>Return the call time values for this function or
<span class="code">true</span> for the pseudo function <span class="code">on_load</span> if call
time tracing is active. Returns <span class="code">false</span> otherwise.
The call time values returned, <span class="code">[{Pid, Count, S, Us}]</span>,
is a list of each process that has executed the function and its specific counters.
See also
<span class="bold_code"><a href="#trace_pattern-3">erlang:trace_pattern/3</a></span>.</p>
</dd>
<dt><strong><span class="code">all</span></strong></dt>
<dd>
<p>Return a list containing the <span class="code">{Item, Value}</span> tuples
for all other items, or return <span class="code">false</span> if no tracing
is active for this function.</p>
</dd>
</dl>
<p>The actual return value will be <span class="code">{Item, Value}</span>, where
<span class="code">Value</span> is the requested information as described above.
If a pid for a dead process was given, or the name of a
non-existing function, <span class="code">Value</span> will be <span class="code">undefined</span>.</p>
<p>If <span class="code">PidOrFunc</span> is the <span class="code">on_load</span>, the information
returned refers to the default value for code that will be
loaded.</p>
</p></div>
<p><a name="trace_pattern-2"><span class="bold_code">erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0</span></a><br></p>
<div class="REFBODY"><p>
<p>The same as
<span class="bold_code"><a href="#trace_pattern-3">erlang:trace_pattern(MFA, MatchSpec, [])</a></span>,
retained for backward compatibility.</p>
</p></div>
<p><a name="trace_pattern-3"><span class="bold_code">erlang:trace_pattern(MFA, MatchSpec, FlagList) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">MFA, MatchSpec, FlagList -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>This BIF is used to enable or disable call tracing for
exported functions. It must be combined with
<span class="bold_code"><a href="#trace-3">erlang:trace/3</a></span>
to set the <span class="code">call</span> trace flag for one or more processes.</p>
<p>Conceptually, call tracing works like this: Inside
the Erlang virtual machine there is a set of processes to be
traced and a set of functions to be traced. Tracing will be
enabled on the intersection of the set. That is, if a process
included in the traced process set calls a function included
in the traced function set, the trace action will be taken.
Otherwise, nothing will happen.</p>
<p>Use
<span class="bold_code"><a href="#trace-3">erlang:trace/3</a></span> to
add or remove one or more processes to the set of traced
processes. Use <span class="code">erlang:trace_pattern/2</span> to add or remove
exported functions to the set of traced functions.</p>
<p>The <span class="code">erlang:trace_pattern/3</span> BIF can also add match
specifications to an exported function. A match specification
comprises a pattern that the arguments to the function must
match, a guard expression which must evaluate to <span class="code">true</span>
and an action to be performed. The default action is to send a
trace message. If the pattern does not match or the guard
fails, the action will not be executed.</p>
<p>The <span class="code">MFA</span> argument should be a tuple like
<span class="code">{Module, Function, Arity}</span> or the atom <span class="code">on_load</span>
(described below). It can be the module, function, and arity
for an exported function (or a BIF in any module).
The <span class="code">'_'</span> atom can be used to mean any of that kind.
Wildcards can be used in any of the following ways:</p>
<dl>
<dt><strong><span class="code">{Module,Function,'_'}</span></strong></dt>
<dd>
<p>All exported functions of any arity named <span class="code">Function</span>
in module <span class="code">Module</span>.</p>
</dd>
<dt><strong><span class="code">{Module,'_','_'}</span></strong></dt>
<dd>
<p>All exported functions in module <span class="code">Module</span>.</p>
</dd>
<dt><strong><span class="code">{'_','_','_'}</span></strong></dt>
<dd>
<p>All exported functions in all loaded modules.</p>
</dd>
</dl>
<p>Other combinations, such as <span class="code">{Module,'_',Arity}</span>, are
not allowed. Local functions will match wildcards only if
the <span class="code">local</span> option is in the <span class="code">FlagList</span>.</p>
<p>If the <span class="code">MFA</span> argument is the atom <span class="code">on_load</span>,
the match specification and flag list will be used on all
modules that are newly loaded.</p>
<p>The <span class="code">MatchSpec</span> argument can take any of the following
forms:</p>
<dl>
<dt><strong><span class="code">false</span></strong></dt>
<dd>
<p>Disable tracing for the matching function(s). Any match
specification will be removed.</p>
</dd>
<dt><strong><span class="code">true</span></strong></dt>
<dd>
<p>Enable tracing for the matching function(s).</p>
</dd>
<dt><strong><span class="code">MatchSpecList</span></strong></dt>
<dd>
<p>A list of match specifications. An empty list is
equivalent to <span class="code">true</span>. See the ERTS User's Guide
for a description of match specifications.</p>
</dd>
<dt><strong><span class="code">restart</span></strong></dt>
<dd>
<p>For the <span class="code">FlagList</span> option <span class="code">call_count</span> and <span class="code">call_time</span>:
restart the existing counters. The behaviour is undefined
for other <span class="code">FlagList</span> options.</p>
</dd>
<dt><strong><span class="code">pause</span></strong></dt>
<dd>
<p>For the <span class="code">FlagList</span> option <span class="code">call_count</span> and <span class="code">call_time</span>: pause
the existing counters. The behaviour is undefined for
other <span class="code">FlagList</span> options.</p>
</dd>
</dl>
<p>The <span class="code">FlagList</span> parameter is a list of options.
The following options are allowed:</p>
<dl>
<dt><strong><span class="code">global</span></strong></dt>
<dd>
<p>Turn on or off call tracing for global function calls
(that is, calls specifying the module explicitly). Only
exported functions will match and only global calls will
generate trace messages. This is the default.</p>
</dd>
<dt><strong><span class="code">local</span></strong></dt>
<dd>
<p>Turn on or off call tracing for all types of function
calls. Trace messages will be sent whenever any of
the specified functions are called, regardless of how they
are called. If the <span class="code">return_to</span> flag is set for
the process, a <span class="code">return_to</span> message will also be sent
when this function returns to its caller.</p>
</dd>
<dt><strong><span class="code">meta | {meta, Pid}</span></strong></dt>
<dd>
<p>Turn on or off meta tracing for all types of function
calls. Trace messages will be sent to the tracer process
or port <span class="code">Pid</span> whenever any of the specified
functions are called, regardless of how they are called.
If no <span class="code">Pid</span> is specified, <span class="code">self()</span> is used as a
default tracer process.</p>
<p>Meta tracing traces all processes and does not care
about the process trace flags set by <span class="code">trace/3</span>,
the trace flags are instead fixed to
<span class="code">[call, timestamp]</span>.</p>
<p>The match spec function <span class="code">{return_trace}</span> works with
meta trace and send its trace message to the same tracer
process.</p>
</dd>
<dt><strong><span class="code">call_count</span></strong></dt>
<dd>
<p>Starts (<span class="code">MatchSpec == true</span>) or stops
(<span class="code">MatchSpec == false</span>) call count tracing for all
types of function calls. For every function a counter is
incremented when the function is called, in any process.
No process trace flags need to be activated.</p>
<p>If call count tracing is started while already running,
the count is restarted from zero. Running counters can be
paused with <span class="code">MatchSpec == pause</span>. Paused and running
counters can be restarted from zero with
<span class="code">MatchSpec == restart</span>.</p>
<p>The counter value can be read with
<span class="bold_code"><a href="#trace_info-2">erlang:trace_info/2</a></span>.</p>
</dd>
<dt><strong><span class="code">call_time</span></strong></dt>
<dd>
<p>Starts (<span class="code">MatchSpec == true</span>) or stops
(<span class="code">MatchSpec == false</span>) call time tracing for all
types of function calls. For every function a counter is
incremented when the function is called. Time spent in the function
is accumulated in two other counters, seconds and micro-seconds.
The counters are stored for each call traced process.</p>
<p>If call time tracing is started while already running,
the count and time is restarted from zero. Running counters can be
paused with <span class="code">MatchSpec == pause</span>. Paused and running
counters can be restarted from zero with
<span class="code">MatchSpec == restart</span>.</p>
<p>The counter value can be read with
<span class="bold_code"><a href="#trace_info-2">erlang:trace_info/2</a></span>.</p>
</dd>
</dl>
<p>The <span class="code">global</span> and <span class="code">local</span> options are mutually
exclusive and <span class="code">global</span> is the default (if no options are
specified). The <span class="code">call_count</span> and <span class="code">meta</span> options
perform a kind of local tracing, and can also not be combined
with <span class="code">global</span>. A function can be either globally or
locally traced. If global tracing is specified for a
specified set of functions; local, meta, call time and call count
tracing for the matching set of local functions will be
disabled, and vice versa.</p>
<p>When disabling trace, the option must match the type of trace
that is set on the function, so that local tracing must be
disabled with the <span class="code">local</span> option and global tracing with
the <span class="code">global</span> option (or no option at all), and so forth.</p>
<p>There is no way to directly change part of a match
specification list. If a function has a match specification,
you can replace it with a completely new one. If you need to
change an existing match specification, use the
<span class="bold_code"><a href="#trace_info-2">erlang:trace_info/2</a></span>
BIF to retrieve the existing match specification.</p>
<p>Returns the number of exported functions that matched
the <span class="code">MFA</span> argument. This will be zero if none matched at
all.</p>
</p></div>
<p><a name="trunc-1"><span class="bold_code">trunc(Number) -> integer()</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Number = number()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer by the truncating <span class="code">Number</span>.</p>
<div class="example"><pre>
> <span class="bold_code">trunc(5.5).</span>
5</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="tuple_size-1"><span class="bold_code">tuple_size(Tuple) -> integer() >= 0</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Tuple = tuple()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns an integer which is the number of elements in <span class="code">Tuple</span>.</p>
<div class="example"><pre>
> <span class="bold_code">tuple_size({morni, mulle, bwange}).</span>
3</pre></div>
<p>Allowed in guard tests.</p>
</p></div>
<p><a name="tuple_to_list-1"><span class="bold_code">tuple_to_list(Tuple) -> [term()]</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Tuple = tuple()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns a list which corresponds to <span class="code">Tuple</span>.
<span class="code">Tuple</span> may contain any Erlang terms.</p>
<div class="example"><pre>
> <span class="bold_code">tuple_to_list({share, {'Ericsson_B', 163}}).</span>
[share,{'Ericsson_B',163}]</pre></div>
</p></div>
<p><a name="universaltime-0"><span class="bold_code">erlang:universaltime() -> DateTime</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">DateTime = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-datetime');">calendar:datetime()</a></span></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the current date and time according to Universal
Time Coordinated (UTC), also called GMT, in the form
<span class="code">{{Year, Month, Day}, {Hour, Minute, Second}}</span> if
supported by the underlying operating system. If not,
<span class="code">erlang:universaltime()</span> is equivalent to
<span class="code">erlang:localtime()</span>.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:universaltime().</span>
{{1996,11,6},{14,18,43}}</pre></div>
</p></div>
<p><a name="universaltime_to_localtime-1"><span class="bold_code">erlang:universaltime_to_localtime({Date1, Time1}) -> {Date2, Time2}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Date1 = Date2 = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-date');">calendar:date()</a></span></span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Time1 = Time2 = <span class="bold_code"><a href="javascript:erlhref('../../../doc/../','stdlib','calendar.html#type-time');">calendar:time()</a></span></span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Converts Universal Time Coordinated (UTC) date and time to
local date and time, if this is supported by the underlying
OS. Otherwise, no conversion is done, and
<span class="code">{Date1, Time1}</span> is returned.</p>
<div class="example"><pre>
> <span class="bold_code">erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).</span>
{{1996,11,7},{15,18,43}}</pre></div>
<p>Failure: <span class="code">badarg</span> if <span class="code">Date1</span> or <span class="code">Time1</span> do
not denote a valid date or time.</p>
</p></div>
<p><a name="unlink-1"><span class="bold_code">unlink(Id) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Id = pid() | port()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Removes the link, if there is one, between the calling
process and the process or port referred to by <span class="code">Id</span>.</p>
<p>Returns <span class="code">true</span> and does not fail, even if there is no
link to <span class="code">Id</span>, or if <span class="code">Id</span> does not exist.</p>
<p>Once <span class="code">unlink(Id)</span> has returned it is guaranteed that
the link between the caller and the entity referred to by
<span class="code">Id</span> has no effect on the caller in the future (unless
the link is setup again). If caller is trapping exits, an
<span class="code">{'EXIT', Id, _}</span> message due to the link might have
been placed in the caller's message queue prior to the call,
though. Note, the <span class="code">{'EXIT', Id, _}</span> message can be the
result of the link, but can also be the result of <span class="code">Id</span>
calling <span class="code">exit/2</span>. Therefore, it <strong>may</strong> be
appropriate to cleanup the message queue when trapping exits
after the call to <span class="code">unlink(Id)</span>, as follow:</p>
<div class="example"><pre>
unlink(Id),
receive
{'EXIT', Id, _} ->
true
after 0 ->
true
end</pre></div>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Prior to OTP release R11B (erts version 5.5) <span class="code">unlink/1</span>
behaved completely asynchronous, i.e., the link was active
until the "unlink signal" reached the linked entity. This
had one undesirable effect, though. You could never know when
you were guaranteed <strong>not</strong> to be effected by the link.</p>
<p>Current behavior can be viewed as two combined operations:
asynchronously send an "unlink signal" to the linked entity
and ignore any future results of the link.</p>
</p></div>
</div>
</p></div>
<p><a name="unregister-1"><span class="bold_code">unregister(RegName) -> true</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">RegName = atom()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Removes the registered name <span class="code">RegName</span>, associated with a
pid or a port identifier.</p>
<div class="example"><pre>
> <span class="bold_code">unregister(db).</span>
true</pre></div>
<p>Users are advised not to unregister system processes.</p>
<p>Failure: <span class="code">badarg</span> if <span class="code">RegName</span> is not a registered
name.</p>
</p></div>
<p><a name="whereis-1"><span class="bold_code">whereis(RegName) -> pid() | port() | undefined</span></a><br></p>
<div class="REFBODY"><p>
<p>Returns the pid or port identifier with the registered name
<span class="code">RegName</span>. Returns <span class="code">undefined</span> if the name is not
registered.</p>
<div class="example"><pre>
> <span class="bold_code">whereis(db).</span>
<0.43.0></pre></div>
</p></div>
<p><a name="yield-0"></a><span class="bold_code">erlang:yield() -> true</span><br></p>
<div class="REFBODY"><p>
<p>Voluntarily let other processes (if any) get a chance to
execute. Using <span class="code">erlang:yield()</span> is similar to
<span class="code">receive after 1 -> ok end</span>, except that <span class="code">yield()</span>
is faster.</p>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p><p>There is seldom or never any need to use this BIF,
especially in the SMP-emulator as other processes will have a
chance to run in another scheduler thread anyway.
Using this BIF without a thorough grasp of how the scheduler
works may cause performance degradation.</p></p></div>
</div>
</p></div>
</div>
<div class="footer">
<hr>
<p>Copyright © 1997-2012 Ericsson AB. All Rights Reserved.</p>
</div>
</div>
</div></body>
</html>
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