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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>MaxRequestsPerChild</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>