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<img alt="Erlang logo" src="../erlang-logo.png"><br><small><a href="users_guide.html">User's Guide</a><br><a href="../pdf/otp-system-documentation-5.9.3.1.pdf">PDF</a><br><a href="../index.html">Top</a></small><p><strong>OTP Design Principles</strong><br><strong>User's Guide</strong><br><small>Version 5.9.3.1</small></p>
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<li id="no" title="Overview" expanded="false">Overview<ul>
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<li title="Starting and Stopping Distributed Applications"><a href="distributed_applications.html#id75164">Starting and Stopping Distributed Applications</a></li>
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<li title="Takeover"><a href="distributed_applications.html#id75408">Takeover</a></li>
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<li title="Generating Boot Scripts"><a href="release_structure.html#id75803">Generating Boot Scripts</a></li>
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<li id="no" title="Release Handling" expanded="false">Release Handling<ul>
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<li title="Release Handling Principles"><a href="release_handling.html#id76299">Release Handling Principles</a></li>
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<li title="Release Upgrade File"><a href="release_handling.html#id77359">Release Upgrade File</a></li>
<li title="Installing a Release"><a href="release_handling.html#id77515">Installing a Release</a></li>
<li title="Updating Application Specifications"><a href="release_handling.html#id77986">Updating Application Specifications</a></li>
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</li>
<li id="loadscrollpos" title="Appup Cookbook" expanded="true">Appup Cookbook<ul>
<li><a href="appup_cookbook.html">
Top of chapter
</a></li>
<li title="Changing a Functional Module"><a href="appup_cookbook.html#id78170">Changing a Functional Module</a></li>
<li title="Changing a Residence Module"><a href="appup_cookbook.html#id78193">Changing a Residence Module</a></li>
<li title="Changing a Callback Module"><a href="appup_cookbook.html#id78232">Changing a Callback Module</a></li>
<li title="Changing Internal State"><a href="appup_cookbook.html#id78283">Changing Internal State</a></li>
<li title="Module Dependencies"><a href="appup_cookbook.html#id78417">Module Dependencies</a></li>
<li title="Changing Code For a Special Process"><a href="appup_cookbook.html#id78588">Changing Code For a Special Process</a></li>
<li title="Changing a Supervisor"><a href="appup_cookbook.html#id78755">Changing a Supervisor</a></li>
<li title="Adding or Deleting a Module"><a href="appup_cookbook.html#id79000">Adding or Deleting a Module</a></li>
<li title="Starting or Terminating a Process"><a href="appup_cookbook.html#id79026">Starting or Terminating a Process</a></li>
<li title="Adding or Removing an Application"><a href="appup_cookbook.html#id79044">Adding or Removing an Application</a></li>
<li title="Restarting an Application"><a href="appup_cookbook.html#id79075">Restarting an Application</a></li>
<li title="Changing an Application Specification"><a href="appup_cookbook.html#id79117">Changing an Application Specification</a></li>
<li title="Changing Application Configuration"><a href="appup_cookbook.html#id79141">Changing Application Configuration</a></li>
<li title="Changing Included Applications"><a href="appup_cookbook.html#id79174">Changing Included Applications</a></li>
<li title="Changing Non-Erlang Code"><a href="appup_cookbook.html#id79414">Changing Non-Erlang Code</a></li>
<li title="Emulator Restart and Upgrade"><a href="appup_cookbook.html#id79499">Emulator Restart and Upgrade</a></li>
<li title="Emulator Upgrade from pre OTP R15"><a href="appup_cookbook.html#id79575">Emulator Upgrade from pre OTP R15</a></li>
</ul>
</li>
</ul>
</div></div>
<div id="content">
<div class="innertube">
<h1>12 Appup Cookbook</h1>
<p>This chapter contains examples of <span class="code">.appup</span> files for
typical cases of upgrades/downgrades done in run-time.</p>
<h3><a name="id78170">12.1
Changing a Functional Module</a></h3>
<p>When a change has been made to a functional module, for example
if a new function has been added or a bug has been corrected,
simple code replacement is sufficient.</p>
<p>Example:</p>
<div class="example"><pre>
{"2",
[{"1", [{load_module, m}]}],
[{"1", [{load_module, m}]}]
}.</pre></div>
<h3><a name="id78193">12.2
Changing a Residence Module</a></h3>
<p>In a system implemented according to the OTP Design Principles,
all processes, except system processes and special processes,
reside in one of the behaviours <span class="code">supervisor</span>,
<span class="code">gen_server</span>, <span class="code">gen_fsm</span> or <span class="code">gen_event</span>. These
belong to the STDLIB application and upgrading/downgrading
normally requires an emulator restart.</p>
<p>OTP thus provides no support for changing residence modules
except in the case of <span class="bold_code"><a href="#spec">special processes</a></span>.</p>
<h3><a name="id78232">12.3
Changing a Callback Module</a></h3>
<p>A callback module is a functional module, and for code
extensions simple code replacement is sufficient.</p>
<p>Example: When adding a function to <span class="code">ch3</span> as described in
the example in <span class="bold_code"><a href="release_handling.html#appup">Release Handling</a></span>, <span class="code">ch_app.appup</span> looks as follows:</p>
<div class="example"><pre>
{"2",
[{"1", [{load_module, ch3}]}],
[{"1", [{load_module, ch3}]}]
}.</pre></div>
<p>OTP also supports changing the internal state of behaviour
processes, see <span class="bold_code"><a href="#int_state">Changing Internal State</a></span> below.</p>
<h3><a name="id78283">12.4
Changing Internal State</a></h3>
<a name="int_state"></a>
<p>In this case, simple code replacement is not sufficient.
The process must explicitly transform its state using the callback
function <span class="code">code_change</span> before switching to the new version
of the callback module. Thus synchronized code replacement is
used.</p>
<p>Example: Consider the gen_server <span class="code">ch3</span> from the chapter
about the <span class="bold_code"><a href="gen_server_concepts.html#ex">gen_server behaviour</a></span>. The internal state is a term <span class="code">Chs</span>
representing the available channels. Assume we want add a counter
<span class="code">N</span> which keeps track of the number of <span class="code">alloc</span> requests
so far. This means we need to change the format to
<span class="code">{Chs,N}</span>.</p>
<p>The <span class="code">.appup</span> file could look as follows:</p>
<div class="example"><pre>
{"2",
[{"1", [{update, ch3, {advanced, []}}]}],
[{"1", [{update, ch3, {advanced, []}}]}]
}.</pre></div>
<p>The third element of the <span class="code">update</span> instruction is a tuple
<span class="code">{advanced,Extra}</span> which says that the affected processes
should do a state transformation before loading the new version
of the module. This is done by the processes calling the callback
function <span class="code">code_change</span> (see <span class="code">gen_server(3)</span>). The term
<span class="code">Extra</span>, in this case [], is passed as-is to the function:</p>
<a name="code_change"></a>
<div class="example"><pre>
-module(ch3).
...
-export([code_change/3]).
...
code_change({down, _Vsn}, {Chs, N}, _Extra) ->
{ok, Chs};
code_change(_Vsn, Chs, _Extra) ->
{ok, {Chs, 0}}.</pre></div>
<p>The first argument is <span class="code">{down,Vsn}</span> in case of a downgrade,
or <span class="code">Vsn</span> in case of an upgrade. The term <span class="code">Vsn</span> is
fetched from the 'original' version of the module, i.e.
the version we are upgrading from, or downgrading to.</p>
<p>The version is defined by the module attribute <span class="code">vsn</span>, if
any. There is no such attribute in <span class="code">ch3</span>, so in this case
the version is the checksum (a huge integer) of the BEAM file, an
uninteresting value which is ignored.</p>
<p>(The other callback functions of <span class="code">ch3</span> need to be modified
as well and perhaps a new interface function added, this is not
shown here).</p>
<h3><a name="id78417">12.5
Module Dependencies</a></h3>
<p>Assume we extend a module by adding a new interface function, as
in the example in <span class="bold_code"><a href="release_handling.html#appup">Release Handling</a></span>, where a function <span class="code">available/0</span> is
added to <span class="code">ch3</span>.</p>
<p>If we also add a call to this function, say in the module
<span class="code">m1</span>, a run-time error could occur during release upgrade if
the new version of <span class="code">m1</span> is loaded first and calls
<span class="code">ch3:available/0</span> before the new version of <span class="code">ch3</span> is
loaded.</p>
<p>Thus, <span class="code">ch3</span> must be loaded before <span class="code">m1</span> is, in
the upgrade case, and vice versa in the downgrade case. We say
that <span class="code">m1</span><strong>is dependent on</strong><span class="code">ch3</span>. In a release
handling instruction, this is expressed by the element
<span class="code">DepMods</span>:</p>
<div class="example"><pre>
{load_module, Module, DepMods}
{update, Module, {advanced, Extra}, DepMods}</pre></div>
<p><span class="code">DepMods</span> is a list of modules, on which <span class="code">Module</span> is
dependent.</p>
<p>Example: The module <span class="code">m1</span> in the application <span class="code">myapp</span> is
dependent on <span class="code">ch3</span> when upgrading from "1" to "2", or
downgrading from "2" to "1":</p>
<div class="example"><pre>
myapp.appup:
{"2",
[{"1", [{load_module, m1, [ch3]}]}],
[{"1", [{load_module, m1, [ch3]}]}]
}.
ch_app.appup:
{"2",
[{"1", [{load_module, ch3}]}],
[{"1", [{load_module, ch3}]}]
}.</pre></div>
<p>If <span class="code">m1</span> and <span class="code">ch3</span> had belonged to the same application,
the <span class="code">.appup</span> file could have looked like this:</p>
<div class="example"><pre>
{"2",
[{"1",
[{load_module, ch3},
{load_module, m1, [ch3]}]}],
[{"1",
[{load_module, ch3},
{load_module, m1, [ch3]}]}]
}.</pre></div>
<p>Note that it is <span class="code">m1</span> that is dependent on <span class="code">ch3</span> also
when downgrading. <span class="code">systools</span> knows the difference between
up- and downgrading and will generate a correct <span class="code">relup</span>,
where <span class="code">ch3</span> is loaded before <span class="code">m1</span> when upgrading but
<span class="code">m1</span> is loaded before <span class="code">ch3</span> when downgrading.</p>
<h3><a name="id78588">12.6
Changing Code For a Special Process</a></h3>
<a name="spec"></a>
<p>In this case, simple code replacement is not sufficient.
When a new version of a residence module for a special process
is loaded, the process must make a fully qualified call to
its loop function to switch to the new code. Thus synchronized
code replacement must be used.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The name(s) of the user-defined residence module(s) must be
listed in the <span class="code">Modules</span> part of the child specification
for the special process, in order for the release handler to
find the process.</p>
</p></div>
</div>
<p>Example. Consider the example <span class="code">ch4</span> from the chapter about
<span class="bold_code"><a href="spec_proc.html#ex">sys and proc_lib</a></span>.
When started by a supervisor, the child specification could look
like this:</p>
<div class="example"><pre>
{ch4, {ch4, start_link, []},
permanent, brutal_kill, worker, [ch4]}</pre></div>
<p>If <span class="code">ch4</span> is part of the application <span class="code">sp_app</span> and a new
version of the module should be loaded when upgrading from
version "1" to "2" of this application, <span class="code">sp_app.appup</span> could
look like this:</p>
<div class="example"><pre>
{"2",
[{"1", [{update, ch4, {advanced, []}}]}],
[{"1", [{update, ch4, {advanced, []}}]}]
}.</pre></div>
<p>The <span class="code">update</span> instruction must contain the tuple
<span class="code">{advanced,Extra}</span>. The instruction will make the special
process call the callback function <span class="code">system_code_change/4</span>, a
function the user must implement. The term <span class="code">Extra</span>, in this
case [], is passed as-is to <span class="code">system_code_change/4</span>:</p>
<div class="example"><pre>
-module(ch4).
...
-export([system_code_change/4]).
...
system_code_change(Chs, _Module, _OldVsn, _Extra) ->
{ok, Chs}.</pre></div>
<p>The first argument is the internal state <span class="code">State</span> passed from
the function <span class="code">sys:handle_system_msg(Request, From, Parent, Module, Deb, State)</span>, called by the special process when
a system message is received. In <span class="code">ch4</span>, the internal state is
the set of available channels <span class="code">Chs</span>.</p>
<p>The second argument is the name of the module (<span class="code">ch4</span>).</p>
<p>The third argument is <span class="code">Vsn</span> or <span class="code">{down,Vsn}</span> as
described for
<span class="bold_code"><a href="#code_change">gen_server:code_change/3</a></span>.</p>
<p>In this case, all arguments but the first are ignored and
the function simply returns the internal state again. This is
enough if the code only has been extended. If we had wanted to
change the internal state (similar to the example in
<span class="bold_code"><a href="#int_state">Changing Internal State</a></span>),
it would have been done in this function and
<span class="code">{ok,Chs2}</span> returned.</p>
<h3><a name="id78755">12.7
Changing a Supervisor</a></h3>
<a name="sup"></a>
<p>The supervisor behaviour supports changing the internal state,
i.e. changing restart strategy and maximum restart frequency
properties, as well as changing existing child specifications.</p>
<p>Adding and deleting child processes are also possible, but not
handled automatically. Instructions must be given by in
the <span class="code">.appup</span> file.</p>
<h4>Changing Properties</h4>
<p>Since the supervisor should change its internal state,
synchronized code replacement is required. However,
a special <span class="code">update</span> instruction must be used.</p>
<p>The new version of the callback module must be loaded first
both in the case of upgrade and downgrade. Then the new return
value of <span class="code">init/1</span> can be checked and the internal state be
changed accordingly.</p>
<p>The following <span class="code">upgrade</span> instruction is used for
supervisors:</p>
<div class="example"><pre>
{update, Module, supervisor}</pre></div>
<p>Example: Assume we want to change the restart strategy of
<span class="code">ch_sup</span> from the <span class="bold_code"><a href="sup_princ.html#ex">Supervisor Behaviour</a></span> chapter from one_for_one to one_for_all.
We change the callback function <span class="code">init/1</span> in
<span class="code">ch_sup.erl</span>:</p>
<div class="example"><pre>
-module(ch_sup).
...
init(_Args) ->
{ok, {{one_for_all, 1, 60}, ...}}.</pre></div>
<p>The file <span class="code">ch_app.appup</span>:</p>
<div class="example"><pre>
{"2",
[{"1", [{update, ch_sup, supervisor}]}],
[{"1", [{update, ch_sup, supervisor}]}]
}.</pre></div>
<h4>Changing Child Specifications</h4>
<p>The instruction, and thus the <span class="code">.appup</span> file, when
changing an existing child specification, is the same as when
changing properties as described above:</p>
<div class="example"><pre>
{"2",
[{"1", [{update, ch_sup, supervisor}]}],
[{"1", [{update, ch_sup, supervisor}]}]
}.</pre></div>
<p>The changes do not affect existing child processes. For
example, changing the start function only specifies how
the child process should be restarted, if needed later on.</p>
<p>Note that the id of the child specification cannot be changed.</p>
<p>Note also that changing the <span class="code">Modules</span> field of the child
specification may affect the release handling process itself,
as this field is used to identify which processes are affected
when doing a synchronized code replacement.</p>
<a name="sup_add"></a>
<h4>Adding And Deleting Child Processes</h4>
<p>As stated above, changing child specifications does not affect
existing child processes. New child specifications are
automatically added, but not deleted. Also, child processes are
not automatically started or terminated. Instead, this must be
done explicitly using <span class="code">apply</span> instructions.</p>
<p>Example: Assume we want to add a new child process <span class="code">m1</span> to
<span class="code">ch_sup</span> when upgrading <span class="code">ch_app</span> from "1" to "2".
This means <span class="code">m1</span> should be deleted when downgrading from
"2" to "1":</p>
<div class="example"><pre>
{"2",
[{"1",
[{update, ch_sup, supervisor},
{apply, {supervisor, restart_child, [ch_sup, m1]}}
]}],
[{"1",
[{apply, {supervisor, terminate_child, [ch_sup, m1]}},
{apply, {supervisor, delete_child, [ch_sup, m1]}},
{update, ch_sup, supervisor}
]}]
}.</pre></div>
<p>Note that the order of the instructions is important.</p>
<p>Note also that the supervisor must be registered as
<span class="code">ch_sup</span> for the script to work. If the supervisor is not
registered, it cannot be accessed directly from the script.
Instead a help function that finds the pid of the supervisor
and calls <span class="code">supervisor:restart_child</span> etc. must be written,
and it is this function that should be called from the script
using the <span class="code">apply</span> instruction.</p>
<p>If the module <span class="code">m1</span> is introduced in version "2" of
<span class="code">ch_app</span>, it must also be loaded when upgrading and
deleted when downgrading:</p>
<div class="example"><pre>
{"2",
[{"1",
[{add_module, m1},
{update, ch_sup, supervisor},
{apply, {supervisor, restart_child, [ch_sup, m1]}}
]}],
[{"1",
[{apply, {supervisor, terminate_child, [ch_sup, m1]}},
{apply, {supervisor, delete_child, [ch_sup, m1]}},
{update, ch_sup, supervisor},
{delete_module, m1}
]}]
}.</pre></div>
<p>Note again that the order of the instructions is important.
When upgrading, <span class="code">m1</span> must be loaded and the supervisor's
child specification changed, before the new child process can
be started. When downgrading, the child process must be
terminated before child specification is changed and the module
is deleted.</p>
<h3><a name="id79000">12.8
Adding or Deleting a Module</a></h3>
<p>Example: A new functional module <span class="code">m</span> is added to
<span class="code">ch_app</span>:</p>
<div class="example"><pre>
{"2",
[{"1", [{add_module, m}]}],
[{"1", [{delete_module, m}]}]</pre></div>
<h3><a name="id79026">12.9
Starting or Terminating a Process</a></h3>
<p>In a system structured according to the OTP design principles,
any process would be a child process belonging to a supervisor,
see <span class="bold_code"><a href="#sup_add">Adding and Deleting Child Processes</a></span> above.</p>
<h3><a name="id79044">12.10
Adding or Removing an Application</a></h3>
<p>When adding or removing an application, no <span class="code">.appup</span> file
is needed. When generating <span class="code">relup</span>, the <span class="code">.rel</span> files
are compared and <span class="code">add_application</span> and
<span class="code">remove_application</span> instructions are added automatically.</p>
<h3><a name="id79075">12.11
Restarting an Application</a></h3>
<p>Restarting an application is useful when a change is too
complicated to be made without restarting the processes, for
example if the supervisor hierarchy has been restructured.</p>
<p>Example: When adding a new child <span class="code">m1</span> to <span class="code">ch_sup</span>, as
in the <span class="bold_code"><a href="#sup_add">example above</a></span>, an
alternative to updating the supervisor is to restart the entire
application:</p>
<div class="example"><pre>
{"2",
[{"1", [{restart_application, ch_app}]}],
[{"1", [{restart_application, ch_app}]}]
}.</pre></div>
<h3><a name="id79117">12.12
Changing an Application Specification</a></h3>
<a name="app_spec"></a>
<p>When installing a release, the application specifications are
automatically updated before evaluating the <span class="code">relup</span> script.
Hence, no instructions are needed in the <span class="code">.appup</span> file:</p>
<div class="example"><pre>
{"2",
[{"1", []}],
[{"1", []}]
}.</pre></div>
<h3><a name="id79141">12.13
Changing Application Configuration</a></h3>
<p>Changing an application configuration by updating the <span class="code">env</span>
key in the <span class="code">.app</span> file is an instance of changing an
application specification, <span class="bold_code"><a href="#app_spec">see above</a></span>.</p>
<p>Alternatively, application configuration parameters can be
added or updated in <span class="code">sys.config</span>.</p>
<h3><a name="id79174">12.14
Changing Included Applications</a></h3>
<p>The release handling instructions for adding, removing and
restarting applications apply to primary applications only.
There are no corresponding instructions for included
applications. However, since an included application is really a
supervision tree with a topmost supervisor, started as a child
process to a supervisor in the including application, a
<span class="code">relup</span> file can be manually created.</p>
<p>Example: Assume we have a release containing an application
<span class="code">prim_app</span> which have a supervisor <span class="code">prim_sup</span> in its
supervision tree.</p>
<p>In a new version of the release, our example application
<span class="code">ch_app</span> should be included in <span class="code">prim_app</span>. That is,
its topmost supervisor <span class="code">ch_sup</span> should be started as a child
process to <span class="code">prim_sup</span>.</p>
<p>1) Edit the code for <span class="code">prim_sup</span>:</p>
<div class="example"><pre>
init(...) ->
{ok, {...supervisor flags...,
[...,
{ch_sup, {ch_sup,start_link,[]},
permanent,infinity,supervisor,[ch_sup]},
...]}}.</pre></div>
<p>2) Edit the <span class="code">.app</span> file for <span class="code">prim_app</span>:</p>
<div class="example"><pre>
{application, prim_app,
[...,
{vsn, "2"},
...,
{included_applications, [ch_app]},
...
]}.</pre></div>
<p>3) Create a new <span class="code">.rel</span> file, including <span class="code">ch_app</span>:</p>
<div class="example"><pre>
{release,
...,
[...,
{prim_app, "2"},
{ch_app, "1"}]}.</pre></div>
<h4>Application Restart</h4>
<p>4a) One way to start the included application is to restart
the entire <span class="code">prim_app</span> application. Normally, we would then
use the <span class="code">restart_application</span> instruction in
the <span class="code">.appup</span> file for <span class="code">prim_app</span>.</p>
<p>However, if we did this and then generated a <span class="code">relup</span> file,
not only would it contain instructions for restarting (i.e.
removing and adding) <span class="code">prim_app</span>, it would also contain
instructions for starting <span class="code">ch_app</span> (and stopping it, in
the case of downgrade). This is due to the fact that
<span class="code">ch_app</span> is included in the new <span class="code">.rel</span> file, but not
in the old one.</p>
<p>Instead, a correct <span class="code">relup</span> file can be created manually,
either from scratch or by editing the generated version.
The instructions for starting/stopping <span class="code">ch_app</span> are
replaced by instructions for loading/unloading the application:</p>
<div class="example"><pre>
{"B",
[{"A",
[],
[{load_object_code,{ch_app,"1",[ch_sup,ch3]}},
{load_object_code,{prim_app,"2",[prim_app,prim_sup]}},
point_of_no_return,
{apply,{application,stop,[prim_app]}},
{remove,{prim_app,brutal_purge,brutal_purge}},
{remove,{prim_sup,brutal_purge,brutal_purge}},
{purge,[prim_app,prim_sup]},
{load,{prim_app,brutal_purge,brutal_purge}},
{load,{prim_sup,brutal_purge,brutal_purge}},
{load,{ch_sup,brutal_purge,brutal_purge}},
{load,{ch3,brutal_purge,brutal_purge}},
{apply,{application,load,[ch_app]}},
{apply,{application,start,[prim_app,permanent]}}]}],
[{"A",
[],
[{load_object_code,{prim_app,"1",[prim_app,prim_sup]}},
point_of_no_return,
{apply,{application,stop,[prim_app]}},
{apply,{application,unload,[ch_app]}},
{remove,{ch_sup,brutal_purge,brutal_purge}},
{remove,{ch3,brutal_purge,brutal_purge}},
{purge,[ch_sup,ch3]},
{remove,{prim_app,brutal_purge,brutal_purge}},
{remove,{prim_sup,brutal_purge,brutal_purge}},
{purge,[prim_app,prim_sup]},
{load,{prim_app,brutal_purge,brutal_purge}},
{load,{prim_sup,brutal_purge,brutal_purge}},
{apply,{application,start,[prim_app,permanent]}}]}]
}.</pre></div>
<h4>Supervisor Change</h4>
<p>4b) Another way to start the included application (or stop it
in the case of downgrade) is by combining instructions for
adding and removing child processes to/from <span class="code">prim_sup</span> with
instructions for loading/unloading all <span class="code">ch_app</span> code and
its application specification.</p>
<p>Again, the <span class="code">relup</span> file is created manually. Either from
scratch or by editing a generated version. Load all code for
<span class="code">ch_app</span> first, and also load the application
specification, before <span class="code">prim_sup</span> is updated. When
downgrading, <span class="code">prim_sup</span> should be updated first, before
the code for <span class="code">ch_app</span> and its application specification
are unloaded.</p>
<div class="example"><pre>
{"B",
[{"A",
[],
[{load_object_code,{ch_app,"1",[ch_sup,ch3]}},
{load_object_code,{prim_app,"2",[prim_sup]}},
point_of_no_return,
{load,{ch_sup,brutal_purge,brutal_purge}},
{load,{ch3,brutal_purge,brutal_purge}},
{apply,{application,load,[ch_app]}},
{suspend,[prim_sup]},
{load,{prim_sup,brutal_purge,brutal_purge}},
{code_change,up,[{prim_sup,[]}]},
{resume,[prim_sup]},
{apply,{supervisor,restart_child,[prim_sup,ch_sup]}}]}],
[{"A",
[],
[{load_object_code,{prim_app,"1",[prim_sup]}},
point_of_no_return,
{apply,{supervisor,terminate_child,[prim_sup,ch_sup]}},
{apply,{supervisor,delete_child,[prim_sup,ch_sup]}},
{suspend,[prim_sup]},
{load,{prim_sup,brutal_purge,brutal_purge}},
{code_change,down,[{prim_sup,[]}]},
{resume,[prim_sup]},
{remove,{ch_sup,brutal_purge,brutal_purge}},
{remove,{ch3,brutal_purge,brutal_purge}},
{purge,[ch_sup,ch3]},
{apply,{application,unload,[ch_app]}}]}]
}.</pre></div>
<h3><a name="id79414">12.15
Changing Non-Erlang Code</a></h3>
<p>Changing code for a program written in another programming
language than Erlang, for example a port program, is very
application dependent and OTP provides no special support for it.</p>
<p>Example, changing code for a port program: Assume that
the Erlang process controlling the port is a gen_server
<span class="code">portc</span> and that the port is opened in the callback function
<span class="code">init/1</span>:</p>
<div class="example"><pre>
init(...) ->
...,
PortPrg = filename:join(code:priv_dir(App), "portc"),
Port = open_port({spawn,PortPrg}, [...]),
...,
{ok, #state{port=Port, ...}}.</pre></div>
<p>If the port program should be updated, we can extend the code for
the gen_server with a <span class="code">code_change</span> function which closes
the old port and opens a new port. (If necessary, the gen_server
may first request data that needs to be saved from the port
program and pass this data to the new port):</p>
<div class="example"><pre>
code_change(_OldVsn, State, port) ->
State#state.port ! close,
receive
{Port,close} ->
true
end,
PortPrg = filename:join(code:priv_dir(App), "portc"),
Port = open_port({spawn,PortPrg}, [...]),
{ok, #state{port=Port, ...}}.</pre></div>
<p>Update the application version number in the <span class="code">.app</span> file
and write an <span class="code">.appup</span> file:</p>
<div class="example"><pre>
["2",
[{"1", [{update, portc, {advanced,port}}]}],
[{"1", [{update, portc, {advanced,port}}]}]
].</pre></div>
<p>Make sure the <span class="code">priv</span> directory where the C program is
located is included in the new release package:</p>
<div class="example"><pre>
1> <span class="bold_code">systools:make_tar("my_release", [{dirs,[priv]}]).</span>
...</pre></div>
<h3><a name="id79499">12.16
Emulator Restart and Upgrade</a></h3>
<p>There are two upgrade instructions that will restart the emulator:</p>
<dl>
<dt><strong><span class="code">restart_new_emulator</span></strong></dt>
<dd>Intended for when erts, kernel, stdlib or sasl is
upgraded. It is automatically added when the relup file is
generated by <span class="code">systools:make_relup/3,4</span>. It is executed
before all other upgrade instructions. See
<span class="bold_code"><a href="release_handling.html#restart_new_emulator_instr">Release
Handling</a></span> for more information about this
instruction.</dd>
<dt><strong><span class="code">restart_emulator</span></strong></dt>
<dd>Used when a restart of the emulator is required after all
other upgrade instructions are executed. See
<span class="bold_code"><a href="release_handling.html#restart_emulator_instr">Release
Handling</a></span> for more information about this
instruction.</dd>
</dl>
<p>If an emulator restart is necessary and no upgrade instructions
are needed, i.e. if the restart itself is enough for the
upgraded applications to start running the new versions, a very
simple <span class="code">.relup</span> file can be created manually:</p>
<div class="example"><pre>
{"B",
[{"A",
[],
[restart_emulator]}],
[{"A",
[],
[restart_emulator]}]
}.</pre></div>
<p>In this case, the release handler framework with automatic
packing and unpacking of release packages, automatic path
updates etc. can be used without having to specify <span class="code">.appup</span>
files.</p>
<h3><a name="id79575">12.17
Emulator Upgrade from pre OTP R15</a></h3>
<p>From OTP R15, an emulator upgrade is performed by restarting
the emulator with new versions of the core applications
(<span class="code">kernel</span>, <span class="code">stdlib</span> and <span class="code">sasl</span>) before loading code
and running upgrade instruction for other applications. For this
to work, the release to upgrade from must includes OTP R15 or
later. For the case where the release to upgrade from includes an
earlier emulator version, <span class="code">systools:make_relup</span> will create a
backwards compatible relup file. This means that all upgrade
instructions will be executed before the emulator is
restarted. The new application code will therefore be loaded into
the old emulator. If the new code is compiled with the new
emulator, there might be cases where the beam format has changed
and beam files can not be loaded. To overcome this problem, the
new code should be compiled with the old emulator.</p>
</div>
<div class="footer">
<hr>
<p>Copyright © 1997-2012 Ericsson AB. All Rights Reserved.</p>
</div>
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