1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- 4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 5 This file is generated from xml source: DO NOT EDIT 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 --> 8<title>event - Apache HTTP Server</title> 9<link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 10<link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 11<link href="/style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="/style/css/prettify.css" /> 12<script src="/style/scripts/prettify.min.js" type="text/javascript"> 13</script> 14 15<link href="/images/favicon.ico" rel="shortcut icon" /></head> 16<body> 17<div id="page-header"> 18<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p> 19<p class="apache">Apache HTTP Server Version 2.4</p> 20<img alt="" src="/images/feather.gif" /></div> 21<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div> 22<div id="path"> 23<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.4</a> > <a href="./">Modules</a></div> 24<div id="page-content"> 25<div id="preamble"><h1>Apache MPM event</h1> 26<div class="toplang"> 27<p><span>Available Languages: </span><a href="/en/mod/event.html" title="English"> en </a> | 28<a href="/fr/mod/event.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p> 29</div> 30<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>A variant of the <code class="module"><a href="/mod/worker.html">worker</a></code> MPM with the goal 31of consuming threads only for connections with active processing</td></tr> 32<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr> 33<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>mpm_event_module</td></tr> 34<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>event.c</td></tr></table> 35<h3>Summary</h3> 36 37 <p>The <code class="module"><a href="/mod/event.html">event</a></code> Multi-Processing Module (MPM) is 38 designed to allow more requests to be served simultaneously by 39 passing off some processing work to supporting threads, freeing up 40 the main threads to work on new requests. It is based on the 41 <code class="module"><a href="/mod/worker.html">worker</a></code> MPM, which implements a hybrid 42 multi-process multi-threaded server. Run-time configuration 43 directives are identical to those provided by 44 <code class="module"><a href="/mod/worker.html">worker</a></code>.</p> 45 46 <p>To use the <code class="module"><a href="/mod/event.html">event</a></code> MPM, add 47 <code>--with-mpm=event</code> to the <code class="program"><a href="/programs/configure.html">configure</a></code> 48 script's arguments when building the <code class="program"><a href="/programs/httpd.html">httpd</a></code>.</p> 49 50</div> 51<div id="quickview"><h3 class="directives">Directives</h3> 52<ul id="toc"> 53<li><img alt="" src="/images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</a></li> 54<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li> 55<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li> 56<li><img alt="" src="/images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li> 57<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li> 58<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li> 59<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li> 60<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li> 61<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li> 62<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li> 63<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li> 64<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li> 65<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li> 66<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li> 67<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li> 68<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li> 69<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li> 70<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li> 71<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li> 72<li><img alt="" src="/images/right.gif" /> <a href="mod_unixd.html#user">User</a></li> 73</ul> 74<h3>Topics</h3> 75<ul id="topics"> 76<li><img alt="" src="/images/down.gif" /> <a href="#how-it-works">How it Works</a></li> 77<li><img alt="" src="/images/down.gif" /> <a href="#requirements">Requirements</a></li> 78</ul><h3>See also</h3> 79<ul class="seealso"> 80<li><a href="worker.html">The worker MPM</a></li> 81</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 82<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 83<div class="section"> 84<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2> 85 <p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client 86 completes the first request, the client can keep the connection 87 open, and send further requests using the same socket. This can 88 save significant overhead in creating TCP connections. However, 89 Apache HTTP Server traditionally keeps an entire child process/thread waiting 90 for data from the client, which brings its own disadvantages. To 91 solve this problem, this MPM uses a dedicated thread to handle both 92 the Listening sockets, all sockets that are in a Keep Alive state, 93 and sockets where the handler and protocol filters have done their work 94 and the only remaining thing to do is send the data to the client. The 95 status page of <code class="module"><a href="/mod/mod_status.html">mod_status</a></code> shows how many connections are 96 in the mentioned states.</p> 97 98 <p>The improved connection handling may not work for certain connection 99 filters that have declared themselves as incompatible with event. In these 100 cases, this MPM will fall back to the behaviour of the 101 <code class="module"><a href="/mod/worker.html">worker</a></code> MPM and reserve one worker thread per connection. 102 All modules shipped with the server are compatible with the event MPM.</p> 103 104 <p>A similar restriction is currently present for requests involving an 105 output filter that needs to read and/or modify the whole response body, 106 like for example mod_ssl, mod_deflate, or mod_include. If the 107 connection to the client blocks while the filter is processing the 108 data, and the amount of data produced by the filter is too big to be 109 buffered in memory, the thread used for the request is not freed while 110 httpd waits until the pending data is sent to the client.</p> 111 112 <p>The MPM assumes that the underlying <code>apr_pollset</code> 113 implementation is reasonably threadsafe. This enables the MPM to 114 avoid excessive high level locking, or having to wake up the listener 115 thread in order to send it a keep-alive socket. This is currently 116 only compatible with KQueue and EPoll.</p> 117 118</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 119<div class="section"> 120<h2><a name="requirements" id="requirements">Requirements</a></h2> 121 <p>This MPM depends on <a class="glossarylink" href="/glossary.html#apr" title="see glossary">APR</a>'s atomic 122 compare-and-swap operations for thread synchronization. If you are 123 compiling for an x86 target and you don't need to support 386s, or 124 you are compiling for a SPARC and you don't need to run on 125 pre-UltraSPARC chips, add 126 <code>--enable-nonportable-atomics=yes</code> to the 127 <code class="program"><a href="/programs/configure.html">configure</a></code> script's arguments. This will cause 128 APR to implement atomic operations using efficient opcodes not 129 available in older CPUs.</p> 130 131 <p>This MPM does not perform well on older platforms which lack good 132 threading, but the requirement for EPoll or KQueue makes this 133 moot.</p> 134 135 <ul> 136 137 <li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended. 138 However, it is possible to run this MPM on FreeBSD 5.2.1, if you 139 use <code>libkse</code> (see <code>man libmap.conf</code>).</li> 140 141 <li>For NetBSD, at least version 2.0 is recommended.</li> 142 143 <li>For Linux, a 2.6 kernel is recommended. It is also necessary to 144 ensure that your version of <code>glibc</code> has been compiled 145 with support for EPoll.</li> 146 147 </ul> 148</div> 149<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 150<div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2> 151<table class="directive"> 152<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr> 153<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr> 154<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr> 155<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr> 156<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr> 157<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr> 158<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr> 159</table> 160 <p>The event MPM handles some connections in an asynchronous way, where 161 request worker threads are only allocated for short periods of time as 162 needed, and other connections with one request worker thread reserved per 163 connection. This can lead to situations where all workers are tied up and 164 no worker thread is available to handle new work on established async 165 connections.</p> 166 167 <p>To mitigate this problem, the event MPM does two things: Firstly, it 168 limits the number of connections accepted per process, depending on the 169 number of idle request workers. Secondly, if all workers are busy, it will 170 close connections in keep-alive state even if the keep-alive timeout has 171 not expired. This allows the respective clients to reconnect to a 172 different process which may still have worker threads available.</p> 173 174 <p>This directive can be used to fine-tune the per-process connection 175 limit. A process will only accept new connections if the current number of 176 connections (not counting connections in the "closing" state) is lower 177 than:</p> 178 179 <p class="indent"><strong> 180 <code class="directive"><a href="/mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> + 181 (<code class="directive">AsyncRequestWorkerFactor</code> * 182 <var>number of idle workers</var>) 183 </strong></p> 184 185 <p>This means the absolute maximum numbers of concurrent connections is:</p> 186 187 <p class="indent"><strong> 188 (<code class="directive">AsyncRequestWorkerFactor</code> + 1) * 189 <code class="directive"><a href="/mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> 190 </strong></p> 191 192 <p><code class="directive"><a href="/mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called 193 <code class="directive">MaxClients</code> prior to version 2.3.13. The above value 194 shows that the old name did not accurately describe its meaning for the event MPM.</p> 195 196 <p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer 197 arguments, e.g "1.5".</p> 198 199 200</div> 201</div> 202<div class="bottomlang"> 203<p><span>Available Languages: </span><a href="/en/mod/event.html" title="English"> en </a> | 204<a href="/fr/mod/event.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p> 205</div><div class="top"><a href="#page-header"><img src="/images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. 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