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Mutex Methods
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<h2 class="title" style="clear: both"><a id="mutexstat"></a>DbEnv::mutex_stat()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::mutex_stat(DB_MUTEX_STAT **statp, u_int32_t flags); </pre>
<p>
The <code class="methodname">DbEnv::mutex_stat()</code> method returns the mutex subsystem
statistics.
</p>
<p>
The <code class="methodname">DbEnv::mutex_stat()</code> method creates a statistical structure of
type <code class="literal">DB_MUTEX_STAT</code> and copies a pointer to it into a user-specified
memory location.
</p>
<p>
Statistical structures are stored in allocated memory. If
application-specific allocation routines have been declared (see
<a class="xref" href="envset_alloc.html" title="DbEnv::set_alloc()">DbEnv::set_alloc()</a>
for more information), they are used to allocate the memory;
otherwise, the standard C library <span class="bold"><strong>malloc</strong></span>(3) is used. The caller is responsible
for deallocating the memory. To deallocate the memory, free the
memory reference; references inside the returned memory need not be
individually freed.
</p>
<p>
The following <code class="literal">DB_MUTEX_STAT</code> fields will be filled in:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>u_int32_t st_mutex_align;</strong></span>
</p>
<p>
The mutex alignment, in bytes.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_mutex_tas_spins;</strong></span>
</p>
<p>
The number of times test-and-set mutexes will spin without blocking.
</p>
</li>
<li>
<p>
<span class="bold"><strong>int st_mutex_cnt;</strong></span>
</p>
<p>
The total number of mutexes configured.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_mutex_free;</strong></span>
</p>
<p>
The number of mutexes currently available.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_mutex_inuse;</strong></span>
</p>
<p>
The number of mutexes currently in use.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_mutex_inuse_max;</strong></span>
</p>
<p>
The maximum number of mutexes ever in use.
</p>
</li>
<li>
<p>
<span class="bold"><strong>roff_t st_regsize;</strong></span>
</p>
<p>
The size of the mutex region, in bytes.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_region_wait;</strong></span>
</p>
<p>
The number of times that a thread of control was forced to wait before
obtaining the mutex region mutex.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_region_nowait;</strong></span>
</p>
<p>
The number of times that a thread of control was able to obtain the
mutex region mutex without waiting.
</p>
</li>
</ul>
</div>
<p>
The <code class="methodname">DbEnv::mutex_stat()</code> method may not be called before the
<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called.
</p>
<p>
The <code class="methodname">DbEnv::mutex_stat()</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="idp53908808"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp53920184"></a>statp</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>statp</strong></span> parameter references memory
into which a pointer to the allocated statistics structure is copied.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp53910312"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or the following value:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">DB_STAT_CLEAR</code>
</p>
<p>
Reset statistics after returning their values.
</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp53917768"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::mutex_stat()</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="idp53938920"></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="idp53937624"></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="idp53917440"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="mutex.html#mutexlist" title="Mutex Methods">Mutex Methods</a>
</p>
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