apache/docs/manual/mod/event.xml

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<modulesynopsis metafile="event.xml.meta">
<name>event</name>
<description>A variant of the <module>worker</module> MPM with the goal
of consuming threads only for connections with active processing</description>
<status>MPM</status>
<sourcefile>event.c</sourcefile>
<identifier>mpm_event_module</identifier>

<summary>
    <p>The <module>event</module> 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
    <module>worker</module> MPM, which implements a hybrid
    multi-process multi-threaded server.  Run-time configuration
    directives are identical to those provided by
    <module>worker</module>.</p>

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

</summary>

<seealso><a href="worker.html">The worker MPM</a></seealso>

<section id="how-it-works"><title>How it Works</title>
    <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 signifigant overhead in creating TCP connections. However,
    Apache HTTP Server 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>

</section>
<section id="requirements"><title>Requirements</title>
    <p>This MPM depends on <glossary>APR</glossary>'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
    <program>configure</program> 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>
</section>

<directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>EnableExceptionHook</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>Group</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>Listen</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ListenBacklog</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>SendBufferSize</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxClients</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxMemFree</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxConnectionsPerChild</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxSpareThreads</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MinSpareThreads</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>PidFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ScoreBoardFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ServerLimit</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>StartServers</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ThreadLimit</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ThreadsPerChild</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ThreadStackSize</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>User</name>
</directivesynopsis>

</modulesynopsis>