1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>DbEnv::mutex_alloc()</title> 7 <link rel="stylesheet" href="apiReference.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> 10 <link rel="up" href="mutex.html" title="Chapter 10. Mutex Methods" /> 11 <link rel="prev" href="mutex.html" title="Chapter 10. Mutex Methods" /> 12 <link rel="next" href="mutexfree.html" title="DbEnv::mutex_free()" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">DbEnv::mutex_alloc()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="mutex.html">Prev</a> </td> 22 <th width="60%" align="center">Chapter 10. 23 Mutex Methods 24 </th> 25 <td width="20%" align="right"> <a accesskey="n" href="mutexfree.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="sect1" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title" style="clear: both"><a id="mutexalloc"></a>DbEnv::mutex_alloc()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db_cxx.h> 39 40int 41DbEnv::mutex_alloc(u_int32_t flags, db_mutex_t *mutexp);</pre> 42 <p> 43 The <code class="methodname">DbEnv::mutex_alloc()</code> method allocates a mutex and returns a 44 reference to it into the memory specified by <span class="bold"><strong>mutexp</strong></span>. 45 </p> 46 <p> 47 The <code class="methodname">DbEnv::mutex_alloc()</code> method may not be called before the 48 <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called. 49 </p> 50 <p> 51 The <code class="methodname">DbEnv::mutex_alloc()</code> <span> 52 53 <span> 54 method either returns a non-zero error value or throws an 55 exception that encapsulates a non-zero error value on 56 failure, and returns 0 on success. 57 </span> 58 </span> 59 </p> 60 <div class="sect2" lang="en" xml:lang="en"> 61 <div class="titlepage"> 62 <div> 63 <div> 64 <h3 class="title"><a id="id1697951"></a>Parameters</h3> 65 </div> 66 </div> 67 </div> 68 <div class="sect3" lang="en" xml:lang="en"> 69 <div class="titlepage"> 70 <div> 71 <div> 72 <h4 class="title"><a id="id1697600"></a>flags</h4> 73 </div> 74 </div> 75 </div> 76 <p> 77 The <span class="bold"><strong>flags</strong></span> parameter must be set to 0 78 or by bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing 79 together one or more of the following values: 80 </p> 81 <div class="itemizedlist"> 82 <ul type="disc"> 83 <li> 84 <p><a id="alloc_DB_MUTEX_PROCESS_ONLY"></a> 85 <code class="literal">DB_MUTEX_PROCESS_ONLY</code> 86 </p> 87 <p> 88 The mutex is associated with a single process. The 89 <a class="xref" href="envfailchk.html" title="DbEnv::failchk()">DbEnv::failchk()</a> method will 90 release mutexes held by any process which has exited. 91 </p> 92 </li> 93 <li> 94 <p><a id="alloc_DB_MUTEX_SELF_BLOCK"></a> 95 <code class="literal">DB_MUTEX_SELF_BLOCK</code> 96 </p> 97 <p> 98 The mutex must be self-blocking. That is, if a thread of control 99 locks the mutex and then attempts to lock the mutex again, the thread 100 of control will block until another thread of control releases the 101 original lock on the mutex, allowing the original thread of control to 102 lock the mutex the second time. Attempting to re-acquire a mutex for 103 which the <code class="literal">DB_MUTEX_SELF_BLOCK</code> flag was not specified will result in 104 undefined behavior. 105 </p> 106 </li> 107 </ul> 108 </div> 109 </div> 110 <div class="sect3" lang="en" xml:lang="en"> 111 <div class="titlepage"> 112 <div> 113 <div> 114 <h4 class="title"><a id="id1698192"></a>mutexp</h4> 115 </div> 116 </div> 117 </div> 118 <p> 119 The <span class="bold"><strong>mutexp</strong></span> parameter references 120 memory into which the mutex reference is copied. 121 </p> 122 </div> 123 </div> 124 <div class="sect2" lang="en" xml:lang="en"> 125 <div class="titlepage"> 126 <div> 127 <div> 128 <h3 class="title"><a id="id1698217"></a>Errors</h3> 129 </div> 130 </div> 131 </div> 132 <p> 133 The <code class="methodname">DbEnv::mutex_alloc()</code> <span> 134 135 <span> 136 method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> 137 exception, encapsulating one of the following non-zero errors, or return one 138 of the following non-zero errors: 139 </span> 140 </span> 141 </p> 142 <div class="sect3" lang="en" xml:lang="en"> 143 <div class="titlepage"> 144 <div> 145 <div> 146 <h4 class="title"><a id="id1698003"></a>EINVAL</h4> 147 </div> 148 </div> 149 </div> 150 <p> 151 An invalid flag value or parameter was specified. 152 </p> 153 </div> 154 </div> 155 <div class="sect2" lang="en" xml:lang="en"> 156 <div class="titlepage"> 157 <div> 158 <div> 159 <h3 class="title"><a id="id1698004"></a>Class</h3> 160 </div> 161 </div> 162 </div> 163 <p> 164 <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> 165 </p> 166 </div> 167 <div class="sect2" lang="en" xml:lang="en"> 168 <div class="titlepage"> 169 <div> 170 <div> 171 <h3 class="title"><a id="id1698212"></a>See Also</h3> 172 </div> 173 </div> 174 </div> 175 <p> 176 <a class="xref" href="mutex.html#mutexlist" title="Mutex Methods">Mutex Methods</a> 177 </p> 178 </div> 179 </div> 180 <div class="navfooter"> 181 <hr /> 182 <table width="100%" summary="Navigation footer"> 183 <tr> 184 <td width="40%" align="left"><a accesskey="p" href="mutex.html">Prev</a> </td> 185 <td width="20%" align="center"> 186 <a accesskey="u" href="mutex.html">Up</a> 187 </td> 188 <td width="40%" align="right"> <a accesskey="n" href="mutexfree.html">Next</a></td> 189 </tr> 190 <tr> 191 <td width="40%" align="left" valign="top">Chapter 10. 192 Mutex Methods 193 </td> 194 <td width="20%" align="center"> 195 <a accesskey="h" href="index.html">Home</a> 196 </td> 197 <td width="40%" align="right" valign="top"> DbEnv::mutex_free()</td> 198 </tr> 199 </table> 200 </div> 201 </body> 202</html> 203