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<h2 class="title" style="clear: both"><a id="mutexalloc"></a>DbEnv::mutex_alloc()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::mutex_alloc(u_int32_t flags, db_mutex_t *mutexp);</pre>
<p>
The <code class="methodname">DbEnv::mutex_alloc()</code> method allocates a mutex and returns a
reference to it into the memory specified by <span class="bold"><strong>mutexp</strong></span>.
</p>
<p>
The <code class="methodname">DbEnv::mutex_alloc()</code> method may not be called before the
<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called.
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<p>
The <code class="methodname">DbEnv::mutex_alloc()</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>
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<h3 class="title"><a id="id1697968"></a>Parameters</h3>
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<h4 class="title"><a id="id1698294"></a>flags</h4>
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<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or by bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing
together one or more of the following values:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="alloc_DB_MUTEX_PROCESS_ONLY"></a>
<code class="literal">DB_MUTEX_PROCESS_ONLY</code>
</p>
<p>
The mutex is associated with a single process. The
<a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a> method will
release mutexes held by any process which has exited.
</p>
</li>
<li>
<p><a id="alloc_DB_MUTEX_SELF_BLOCK"></a>
<code class="literal">DB_MUTEX_SELF_BLOCK</code>
</p>
<p>
The mutex must be self-blocking. That is, if a thread of control
locks the mutex and then attempts to lock the mutex again, the thread
of control will block until another thread of control releases the
original lock on the mutex, allowing the original thread of control to
lock the mutex the second time. Attempting to re-acquire a mutex for
which the <code class="literal">DB_MUTEX_SELF_BLOCK</code> flag was not specified will result in
undefined behavior.
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<h4 class="title"><a id="id1698485"></a>mutexp</h4>
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<p>
The <span class="bold"><strong>mutexp</strong></span> parameter references
memory into which the mutex reference is copied.
</p>
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<h3 class="title"><a id="id1698236"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::mutex_alloc()</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>
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<div>
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<h4 class="title"><a id="id1697976"></a>EINVAL</h4>
</div>
</div>
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<p>
An invalid flag value or parameter was specified.
</p>
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<h3 class="title"><a id="id1697977"></a>Class</h3>
</div>
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<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
</p>
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<h3 class="title"><a id="id1697980"></a>See Also</h3>
</div>
</div>
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<p>
<a class="xref" href="mutex.html#mutexlist" title="Mutex Methods">Mutex Methods</a>
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