<?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_set_align()</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="mutexlock.html" title="DbEnv::mutex_lock()" />
    <link rel="next" href="mutexset_increment.html" title="DbEnv::mutex_set_increment()" />
  </head>
  <body>
    <div xmlns="" class="navheader">
      <div class="libver">
        <p>Library Version 12.1.6.1</p>
      </div>
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">DbEnv::mutex_set_align()</th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="mutexlock.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 10. 
                Mutex Methods 
        </th>
          <td width="20%" align="right"> <a accesskey="n" href="mutexset_increment.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="mutexset_align"></a>DbEnv::mutex_set_align()</h2>
          </div>
        </div>
      </div>
      <pre class="programlisting">#include &lt;db_cxx.h&gt;

int
DbEnv::mutex_set_align(u_int32_t align); </pre>
      <p>
        Set the mutex alignment, in bytes.
    </p>
      <p>
         It is sometimes advantageous to align mutexes on specific byte
         boundaries in order to minimize cache line collisions.   The
         <code class="methodname">DbEnv::mutex_set_align()</code> method specifies an alignment for mutexes
         allocated by Berkeley DB.
    </p>
      <p>
         The database environment's mutex alignment may also be configured
         using the environment's <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file. The
         syntax of the entry in that file is a single line with the string
         "mutex_set_align", one or more whitespace characters, and the mutex
         alignment in bytes. Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file is
         read when the database environment is opened, it will silently
         overrule configuration done before that time.
    </p>
      <p>
         The <code class="methodname">DbEnv::mutex_set_align()</code> method configures a database
         environment, not only operations performed using the specified 
         <a class="link" href="env.html" title="Chapter 5.  The DbEnv Handle">DbEnv</a>  handle.
    </p>
      <p>
         The <code class="methodname">DbEnv::mutex_set_align()</code> method may not be called after the
         <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>  method is
         called. If the database environment already exists when 
         <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>  is called, the
         information specified to <code class="methodname">DbEnv::mutex_set_align()</code> will be ignored.
    </p>
      <p>
         The <code class="methodname">DbEnv::mutex_set_align()</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="idp4960576"></a>Parameters</h3>
            </div>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idp4959928"></a>align</h4>
              </div>
            </div>
          </div>
          <p>
                          The <span class="bold"><strong>align</strong></span> parameter is the mutex
                          alignment, in bytes.  The mutex alignment must be a power-of-two.
                     </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="idp4957104"></a>Errors</h3>
            </div>
          </div>
        </div>
        <p>
                         The <code class="methodname">DbEnv::mutex_set_align()</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="idp4969920"></a>EINVAL</h4>
              </div>
            </div>
          </div>
          <p>
                If the method was called after <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> 
                was called; or if 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="idp4971248"></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="idp4961440"></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="mutexlock.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="mutexset_increment.html">Next</a></td>
        </tr>
        <tr>
          <td width="40%" align="left" valign="top">DbEnv::mutex_lock() </td>
          <td width="20%" align="center">
            <a accesskey="h" href="index.html">Home</a>
          </td>
          <td width="40%" align="right" valign="top"> DbEnv::mutex_set_increment()</td>
        </tr>
      </table>
    </div>
  </body>
</html>
