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<h2 class="title" style="clear: both"><a id="envfailchk"></a>DbEnv::failchk()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::failchk(u_int32_t flags);</pre>
<p>
The <code class="methodname">DbEnv::failchk()</code> method checks for threads of control (either a
true thread or a process) that have exited while manipulating Berkeley
DB library data structures, while holding a logical database lock, or
with an unresolved transaction (that is, a transaction that was never
aborted or committed). For more information, see
<a href="../../programmer_reference/cam_app.html" class="olink">Architecting Data Store and
Concurrent Data Store applications</a>, and
<a href="../../programmer_reference/transapp_app.html" class="olink">Architecting Transactional
Data Store applications</a>, both in the
<em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
<p>
The <code class="methodname">DbEnv::failchk()</code> method is
used in conjunction with the
<a class="xref" href="envset_thread_count.html" title="DbEnv::set_thread_count()">DbEnv::set_thread_count()</a>,
<a class="xref" href="envset_isalive.html" title="DbEnv::set_isalive()">DbEnv::set_isalive()</a> and
<a class="xref" href="envset_thread_id.html" title="DbEnv::set_thread_id()">DbEnv::set_thread_id()</a>
methods. Before calling the <code class="methodname">failchk()</code>method, applications must:
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Configure their database using the
<a class="xref" href="envset_thread_count.html" title="DbEnv::set_thread_count()">DbEnv::set_thread_count()</a>
method.
</p>
</li>
<li>
<p>
Establish an <code class="literal">is_alive()</code> function and
invoke
<a class="xref" href="envset_isalive.html" title="DbEnv::set_isalive()">DbEnv::set_isalive()</a>
with that function as the <code class="literal">is_alive</code> parameter.
</p>
</li>
<li>
<p>
Establish a <code class="literal">thread_id</code> function and
invoke
<a class="xref" href="envset_thread_id.html" title="DbEnv::set_thread_id()">DbEnv::set_thread_id()</a>
with that function as the <code class="literal">thread_id</code>
parameter.
</p>
</li>
</ol>
</div>
<p>
If any of these methods are omitted, a program may be unable to
allocate a thread control block. This is true of the standalone
Berkeley DB utility programs. To avoid problems when using the
standalone Berkeley DB utility programs with environments
configured for failure checking, incorporate the utility's
functionality directly in the application, or call the
<code class="methodname">DbEnv::failchk()</code> method along with its
associated methods before running the utility.
</p>
<p>
If <code class="methodname">DbEnv::failchk()</code> determines a thread of control exited while
holding database read locks, it will release those locks. If
<code class="methodname">DbEnv::failchk()</code> determines a thread of control exited with an
unresolved transaction, the transaction will be aborted. In either of
these cases, <code class="methodname">DbEnv::failchk()</code> will return 0 and the application may
continue to use the database environment.
</p>
<p>
In either of these cases, the <code class="methodname">DbEnv::failchk()</code> method will also
report the process and thread IDs associated with any released locks
or aborted transactions. The information is printed to a specified
output channel (see the
<a class="xref" href="envset_msgfile.html" title="DbEnv::set_msgfile()">DbEnv::set_msgfile()</a>
method for more information), or passed to an application callback
function (see the
<a class="xref" href="envset_msgcall.html" title="DbEnv::set_msgcall()">DbEnv::set_msgcall()</a>
method for more information).
</p>
<p>
If <code class="methodname">DbEnv::failchk()</code> determines a thread of control has exited such
that database environment recovery is required, it will return
<a href="../../programmer_reference/program_errorret.html#program_errorret.DB_RUNRECOVERY" class="olink">DB_RUNRECOVERY</a>.
In this case, the application should not continue to use the database
environment. For a further description as to the actions the
application should take when this failure occurs, see
<a href="../../programmer_reference/cam_fail.html" class="olink">Handling failure in Data Store and
Concurrent Data Store applications</a>, and
<a href="../../programmer_reference/transapp_fail.html" class="olink">Handling failure in Transactional Data
Store applications</a>, both in the
<em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
<p>
In multiprocess applications, it is recommended that the <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle
used to invoke the <code class="methodname">DbEnv::failchk()</code> method not be shared and therefore
not <span class="emphasis"><em>free-threaded</em></span>.
</p>
<p>
The <code class="methodname">DbEnv::failchk()</code> method may not be called by the
application before the <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
method is called.
</p>
<p>
The <code class="methodname">DbEnv::failchk()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp6751008"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp6750360"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter is currently
unused, and must be set to 0.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp6755536"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::failchk()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp6768072"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp6766776"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp6769400"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a>
</p>
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