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<title>6.13 mutex -- Mutual exclusion support</title>
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<H1><A NAME="SECTION0081300000000000000000">
6.13 <tt class="module">mutex</tt> --
         Mutual exclusion support</A>
</H1>

<P>
<A NAME="module-mutex"></A>

<P>
The <tt class="module">mutex</tt> module defines a class that allows mutual-exclusion
via acquiring and releasing locks. It does not require (or imply)
threading or multi-tasking, though it could be useful for
those purposes.

<P>
The <tt class="module">mutex</tt> module defines the following class:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-1988' xml:id='l2h-1988' class="class">mutex</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Create a new (unlocked) mutex.

<P>
A mutex has two pieces of state -- a ``locked'' bit and a queue.
When the mutex is not locked, the queue is empty.
Otherwise, the queue contains zero or more
<code>(<var>function</var>, <var>argument</var>)</code> pairs
representing functions (or methods) waiting to acquire the lock.
When the mutex is unlocked while the queue is not empty,
the first queue entry is removed and its
<code><var>function</var>(<var>argument</var>)</code> pair called,
implying it now has the lock.

<P>
Of course, no multi-threading is implied - hence the funny interface
for <tt class="method">lock()</tt>, where a function is called once the lock is
acquired.
</dl>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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