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<div class="section" id="module-mutex">
<h1>8.9. <tt class="xref docutils literal"><span class="pre">mutex</span></tt> — Mutual exclusion support<a class="headerlink" href="#module-mutex" title="Permalink to this headline">¶</a></h1>
<p class="deprecated">
<span class="versionmodified">Deprecated since version 2.6: </span>The <tt class="xref docutils literal"><span class="pre">mutex</span></tt> module has been removed in Python 3.0.</p>
<p>The <tt class="xref docutils literal"><span class="pre">mutex</span></tt> module defines a class that allows mutual-exclusion via
acquiring and releasing locks. It does not require (or imply)
<a title="Higher-level threading interface." class="reference external" href="threading.html#module-threading"><tt class="xref docutils literal"><span class="pre">threading</span></tt></a> or multi-tasking, though it could be useful for those
purposes.</p>
<p>The <tt class="xref docutils literal"><span class="pre">mutex</span></tt> module defines the following class:</p>
<dl class="class">
<dt id="mutex.mutex">
<em class="property">class </em><tt class="descclassname">mutex.</tt><tt class="descname">mutex</tt><a class="headerlink" href="#mutex.mutex" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a new (unlocked) mutex.</p>
<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
<tt class="docutils literal"><span class="pre">(function,</span> <span class="pre">argument)</span></tt> 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 <tt class="docutils literal"><span class="pre">function(argument)</span></tt> pair called,
implying it now has the lock.</p>
<p>Of course, no multi-threading is implied – hence the funny interface for
<a title="mutex.mutex.lock" class="reference internal" href="#mutex.mutex.lock"><tt class="xref docutils literal"><span class="pre">lock()</span></tt></a>, where a function is called once the lock is acquired.</p>
</dd></dl>
<div class="section" id="mutex-objects">
<span id="id1"></span><h2>8.9.1. Mutex Objects<a class="headerlink" href="#mutex-objects" title="Permalink to this headline">¶</a></h2>
<p><a title="mutex.mutex" class="reference internal" href="#mutex.mutex"><tt class="xref docutils literal"><span class="pre">mutex</span></tt></a> objects have following methods:</p>
<dl class="method">
<dt id="mutex.mutex.test">
<tt class="descclassname">mutex.</tt><tt class="descname">test</tt><big>(</big><big>)</big><a class="headerlink" href="#mutex.mutex.test" title="Permalink to this definition">¶</a></dt>
<dd>Check whether the mutex is locked.</dd></dl>
<dl class="method">
<dt id="mutex.mutex.testandset">
<tt class="descclassname">mutex.</tt><tt class="descname">testandset</tt><big>(</big><big>)</big><a class="headerlink" href="#mutex.mutex.testandset" title="Permalink to this definition">¶</a></dt>
<dd>“Atomic” test-and-set, grab the lock if it is not set, and return <tt class="xref docutils literal"><span class="pre">True</span></tt>,
otherwise, return <tt class="xref docutils literal"><span class="pre">False</span></tt>.</dd></dl>
<dl class="method">
<dt id="mutex.mutex.lock">
<tt class="descclassname">mutex.</tt><tt class="descname">lock</tt><big>(</big><em>function</em>, <em>argument</em><big>)</big><a class="headerlink" href="#mutex.mutex.lock" title="Permalink to this definition">¶</a></dt>
<dd>Execute <tt class="docutils literal"><span class="pre">function(argument)</span></tt>, unless the mutex is locked. In the case it is
locked, place the function and argument on the queue. See <a title="mutex.mutex.unlock" class="reference internal" href="#mutex.mutex.unlock"><tt class="xref docutils literal"><span class="pre">unlock()</span></tt></a> for
explanation of when <tt class="docutils literal"><span class="pre">function(argument)</span></tt> is executed in that case.</dd></dl>
<dl class="method">
<dt id="mutex.mutex.unlock">
<tt class="descclassname">mutex.</tt><tt class="descname">unlock</tt><big>(</big><big>)</big><a class="headerlink" href="#mutex.mutex.unlock" title="Permalink to this definition">¶</a></dt>
<dd>Unlock the mutex if queue is empty, otherwise execute the first element in the
queue.</dd></dl>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">8.9. <tt class="docutils literal"><span class="pre">mutex</span></tt> — Mutual exclusion support</a><ul>
<li><a class="reference external" href="#mutex-objects">8.9.1. Mutex Objects</a></li>
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