<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>DbEnv::mutex_alloc()</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> <link rel="up" href="mutex.html" title="Chapter 10. Mutex Methods" /> <link rel="prev" href="mutex.html" title="Chapter 10. Mutex Methods" /> <link rel="next" href="mutexfree.html" title="DbEnv::mutex_free()" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DbEnv::mutex_alloc()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="mutex.html">Prev</a> </td> <th width="60%" align="center">Chapter 10. Mutex Methods </th> <td width="20%" align="right"> <a accesskey="n" href="mutexfree.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="mutexalloc"></a>DbEnv::mutex_alloc()</h2> </div> </div> </div> <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. </p> <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> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1697951"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1697600"></a>flags</h4> </div> </div> </div> <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. </p> </li> </ul> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1698192"></a>mutexp</h4> </div> </div> </div> <p> The <span class="bold"><strong>mutexp</strong></span> parameter references memory into which the mutex reference is copied. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1698217"></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> </p> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1698003"></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="id1698004"></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="id1698212"></a>See Also</h3> </div> </div> </div> <p> <a class="xref" href="mutex.html#mutexlist" title="Mutex Methods">Mutex Methods</a> </p> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="mutex.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="mutex.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="mutexfree.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Chapter 10. Mutex Methods </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DbEnv::mutex_free()</td> </tr> </table> </div> </body> </html>