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<p class="apache">Apache HTTP Server Version 2.2</p>
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<div id="preamble"><h1>Apache MPM event</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/event.html" title="English">&nbsp;en&nbsp;</a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>An experimental variant of the standard <code class="module"><a href="../mod/worker.html">worker</a></code>
MPM</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_event_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>event.c</td></tr></table>
<h3>Summary</h3>

    <div class="warning"><h3>Warning</h3>
      <p>This MPM is experimental, so it may or may not work as
      expected.</p> 
    </div>

    <p>The <code class="module"><a href="../mod/event.html">event</a></code> Multi-Processing Module (MPM) is
    designed to allow more requests to be served simultaneously by
    passing off some processing work to supporting threads, freeing up
    the main threads to work on new requests.  It is based on the
    <code class="module"><a href="../mod/worker.html">worker</a></code> MPM, which implements a hybrid
    multi-process multi-threaded server.  Run-time configuration
    directives are identical to those provided by
    <code class="module"><a href="../mod/worker.html">worker</a></code>.</p>

    <p>To use the <code class="module"><a href="../mod/event.html">event</a></code> MPM, add
      <code>--with-mpm=event</code> to the <code class="program"><a href="../programs/configure.html">configure</a></code>
      script's arguments when building the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</p>

</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
</ul><h3>See also</h3>
<ul class="seealso">
<li><a href="worker.html">The worker MPM</a></li>
</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
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<div class="section">
<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
    <p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client
    completes the first request, the client can keep the connection
    open, and send further requests using the same socket. This can
    save significant overhead in creating TCP connections. However,
    Apache traditionally keeps an entire child process/thread waiting
    for data from the client, which brings its own disadvantages. To
    solve this problem, this MPM uses a dedicated thread to handle both
    the Listening sockets, and all sockets that are in a Keep Alive
    state.</p>

    <p>The MPM assumes that the underlying <code>apr_pollset</code>
    implementation is reasonably threadsafe. This enables the MPM to
    avoid excessive high level locking, or having to wake up the listener
    thread in order to send it a keep-alive socket. This is currently
    only compatible with KQueue and EPoll.</p>

</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="requirements" id="requirements">Requirements</a></h2>
    <p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
    compare-and-swap operations for thread synchronization. If you are
    compiling for an x86 target and you don't need to support 386s, or
    you are compiling for a SPARC and you don't need to run on
    pre-UltraSPARC chips, add
    <code>--enable-nonportable-atomics=yes</code> to the
    <code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
    APR to implement atomic operations using efficient opcodes not
    available in older CPUs.</p>

    <p>This MPM does not perform well on older platforms which lack good
    threading, but the requirement for EPoll or KQueue makes this
    moot.</p>

    <ul>
    
      <li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
      However, it is possible to run this MPM on FreeBSD 5.2.1, if you
      use <code>libkse</code> (see <code>man libmap.conf</code>).</li>

      <li>For NetBSD, at least version 2.0 is recommended.</li>

      <li>For Linux, a 2.6 kernel is recommended. It is also necessary to
      ensure that your version of <code>glibc</code> has been compiled
      with support for EPoll.</li>

    </ul>
</div>
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