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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Chapter 7. Wait Queues include/linux/wait.h</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><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="ch06s13.html" title="try_module_get()/module_put() include/linux/module.h" /><link rel="next" href="ch07s02.html" title="Queuing" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 7. Wait Queues
<code class="filename">include/linux/wait.h</code>
</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch06s13.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch07s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 7. Wait Queues include/linux/wait.h"><div class="titlepage"><div><div><h2 class="title"><a id="queues"></a>Chapter 7. Wait Queues
<code class="filename">include/linux/wait.h</code>
</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch07.html#queue-declaring">Declaring</a></span></dt><dt><span class="sect1"><a href="ch07s02.html">Queuing</a></span></dt><dt><span class="sect1"><a href="ch07s03.html">Waking Up Queued Tasks</a></span></dt></dl></div><p>
<span class="emphasis"><em>[SLEEPS]</em></span>
</p><p>
A wait queue is used to wait for someone to wake you up when a
certain condition is true. They must be used carefully to ensure
there is no race condition. You declare a
<span class="type">wait_queue_head_t</span>, and then processes which want to
wait for that condition declare a <span class="type">wait_queue_t</span>
referring to themselves, and place that in the queue.
</p><div class="sect1" title="Declaring"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="queue-declaring"></a>Declaring</h2></div></div></div><p>
You declare a <span class="type">wait_queue_head_t</span> using the
<code class="function">DECLARE_WAIT_QUEUE_HEAD()</code> macro, or using the
<code class="function">init_waitqueue_head()</code> routine in your
initialization code.
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