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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>

<P>

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	54
	55	<H1><A NAME="SECTION0081300000000000000000">
	56	6.13 <tt class="module">mutex</tt> --
	57	Mutual exclusion support</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-mutex"></A>
	62
	63	<P>
	64	The <tt class="module">mutex</tt> module defines a class that allows mutual-exclusion
65	via acquiring and releasing locks. It does not require (or imply)
66	threading or multi-tasking, though it could be useful for
67	those purposes.
68
69	<P>
70	The <tt class="module">mutex</tt> module defines the following class:
71
72	<P>
73	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
74	<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-1988' xml:id='l2h-1988' class="class">mutex</tt></b>(</nobr></td>
75	<td><var></var>)</td></tr></table></dt>
76	<dd>
77	Create a new (unlocked) mutex.
78
79	<P>
80	A mutex has two pieces of state -- a ``locked'' bit and a queue.
81	When the mutex is not locked, the queue is empty.
82	Otherwise, the queue contains zero or more
83	<code>(<var>function</var>, <var>argument</var>)</code> pairs
84	representing functions (or methods) waiting to acquire the lock.
85	When the mutex is unlocked while the queue is not empty,
86	the first queue entry is removed and its
87	<code><var>function</var>(<var>argument</var>)</code> pair called,
88	implying it now has the lock.
89
90	<P>
91	Of course, no multi-threading is implied - hence the funny interface
92	for <tt class="method">lock()</tt>, where a function is called once the lock is
93	acquired.
94	</dl>
95
96	<P>
97
98	<p><br /></p><hr class='online-navigation' />
99	<div class='online-navigation'>
100	<!--Table of Child-Links-->
101	<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
102
103	<UL CLASS="ChildLinks">
104	<LI><A href="mutex-objects.html">6.13.1 Mutex Objects</a>
105	</ul>
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