1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>Chapter&#160;7.&#160;Wait Queues include/linux/wait.h</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel"><link rel="up" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel"><link rel="prev" href="routines-module-use-counters.html" title="try_module_get()/module_put() include/linux/module.h"><link rel="next" href="queue-waitqueue.html" title="Queuing"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter&#160;7.&#160;Wait Queues
2   <code class="filename">include/linux/wait.h</code>
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4   <code class="filename">include/linux/wait.h</code>
5  </h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="sect1"><a href="queues.html#queue-declaring">Declaring</a></span></dt><dt><span class="sect1"><a href="queue-waitqueue.html">Queuing</a></span></dt><dt><span class="sect1"><a href="queue-waking.html">Waking Up Queued Tasks</a></span></dt></dl></div><p>
6   <span class="emphasis"><em>[SLEEPS]</em></span>
7  </p><p>
8   A wait queue is used to wait for someone to wake you up when a
9   certain condition is true.  They must be used carefully to ensure
10   there is no race condition.  You declare a
11   <span class="type">wait_queue_head_t</span>, and then processes which want to
12   wait for that condition declare a <span class="type">wait_queue_t</span>
13   referring to themselves, and place that in the queue.
14  </p><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="queue-declaring"></a>Declaring</h2></div></div></div><p>
15    You declare a <span class="type">wait_queue_head_t</span> using the
16    <code class="function">DECLARE_WAIT_QUEUE_HEAD()</code> macro, or using the
17    <code class="function">init_waitqueue_head()</code> routine in your
18    initialization code.
19   </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="routines-module-use-counters.html">Prev</a>&#160;</td><td width="20%" align="center">&#160;</td><td width="40%" align="right">&#160;<a accesskey="n" href="queue-waitqueue.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> <code class="function">try_module_get()</code>/<code class="function">module_put()</code>
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21