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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>Queuing</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="ch07.html" title="Chapter 7. Wait Queues include/linux/wait.h" /><link rel="prev" href="ch07.html" title="Chapter 7. Wait Queues include/linux/wait.h" /><link rel="next" href="ch07s03.html" title="Waking Up Queued Tasks" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Queuing</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch07.html">Prev</a> </td><th width="60%" align="center">Chapter 7. Wait Queues
<code class="filename">include/linux/wait.h</code>
</th><td width="20%" align="right"> <a accesskey="n" href="ch07s03.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="Queuing"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="queue-waitqueue"></a>Queuing</h2></div></div></div><p>
Placing yourself in the waitqueue is fairly complex, because you
must put yourself in the queue before checking the condition.
There is a macro to do this:
<code class="function">wait_event_interruptible()</code>
<code class="filename">include/linux/wait.h</code> The
first argument is the wait queue head, and the second is an
expression which is evaluated; the macro returns
<span class="returnvalue">0</span> when this expression is true, or
<span class="returnvalue">-ERESTARTSYS</span> if a signal is received.
The <code class="function">wait_event()</code> version ignores signals.
</p><p>
Do not use the <code class="function">sleep_on()</code> function family -
it is very easy to accidentally introduce races; almost certainly
one of the <code class="function">wait_event()</code> family will do, or a
loop around <code class="function">schedule_timeout()</code>. If you choose
to loop around <code class="function">schedule_timeout()</code> remember
you must set the task state (with
<code class="function">set_current_state()</code>) on each iteration to avoid
busy-looping.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch07.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch07.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch07s03.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 7. Wait Queues
<code class="filename">include/linux/wait.h</code>
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