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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>8.9. mutex — Mutual exclusion support — Python 2.7.16 documentation</title> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.16 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="8.10. Queue — A synchronized queue class" href="queue.html" /> <link rel="prev" title="8.8. sched — Event scheduler" href="sched.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/2/library/mutex.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="queue.html" title="8.10. Queue — A synchronized queue class" accesskey="N">next</a> |</li> <li class="right" > <a href="sched.html" title="8.8. sched — Event scheduler" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.16 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="datatypes.html" accesskey="U">8. Data Types</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-mutex"> <span id="mutex-mutual-exclusion-support"></span><h1>8.9. <a class="reference internal" href="#module-mutex" title="mutex: Lock and queue for mutual exclusion. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">mutex</span></code></a> — Mutual exclusion support<a class="headerlink" href="#module-mutex" title="Permalink to this headline">¶</a></h1> <div class="deprecated"> <p><span class="versionmodified">Deprecated since version 2.6: </span>The <a class="reference internal" href="#module-mutex" title="mutex: Lock and queue for mutual exclusion. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">mutex</span></code></a> module has been removed in Python 3.</p> </div> <p>The <a class="reference internal" href="#module-mutex" title="mutex: Lock and queue for mutual exclusion. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">mutex</span></code></a> module defines a class that allows mutual-exclusion via acquiring and releasing locks. It does not require (or imply) <a class="reference internal" href="threading.html#module-threading" title="threading: Higher-level threading interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> or multi-tasking, though it could be useful for those purposes.</p> <p>The <a class="reference internal" href="#module-mutex" title="mutex: Lock and queue for mutual exclusion. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">mutex</span></code></a> module defines the following class:</p> <dl class="class"> <dt id="mutex.mutex"> <em class="property">class </em><code class="descclassname">mutex.</code><code class="descname">mutex</code><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 <code class="docutils literal notranslate"><span class="pre">(function,</span> <span class="pre">argument)</span></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 class="docutils literal notranslate"><span class="pre">function(argument)</span></code> pair called, implying it now has the lock.</p> <p>Of course, no multi-threading is implied – hence the funny interface for <a class="reference internal" href="#mutex.mutex.lock" title="mutex.mutex.lock"><code class="xref py py-meth docutils literal notranslate"><span class="pre">lock()</span></code></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 class="reference internal" href="#mutex.mutex" title="mutex.mutex"><code class="xref py py-class docutils literal notranslate"><span class="pre">mutex</span></code></a> objects have following methods:</p> <dl class="method"> <dt id="mutex.mutex.test"> <code class="descclassname">mutex.</code><code class="descname">test</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mutex.mutex.test" title="Permalink to this definition">¶</a></dt> <dd><p>Check whether the mutex is locked.</p> </dd></dl> <dl class="method"> <dt id="mutex.mutex.testandset"> <code class="descclassname">mutex.</code><code class="descname">testandset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mutex.mutex.testandset" title="Permalink to this definition">¶</a></dt> <dd><p>“Atomic” test-and-set, grab the lock if it is not set, and return <code class="docutils literal notranslate"><span class="pre">True</span></code>, otherwise, return <code class="docutils literal notranslate"><span class="pre">False</span></code>.</p> </dd></dl> <dl class="method"> <dt id="mutex.mutex.lock"> <code class="descclassname">mutex.</code><code class="descname">lock</code><span class="sig-paren">(</span><em>function</em>, <em>argument</em><span class="sig-paren">)</span><a class="headerlink" href="#mutex.mutex.lock" title="Permalink to this definition">¶</a></dt> <dd><p>Execute <code class="docutils literal notranslate"><span class="pre">function(argument)</span></code>, unless the mutex is locked. In the case it is locked, place the function and argument on the queue. See <a class="reference internal" href="#mutex.mutex.unlock" title="mutex.mutex.unlock"><code class="xref py py-meth docutils literal notranslate"><span class="pre">unlock()</span></code></a> for explanation of when <code class="docutils literal notranslate"><span class="pre">function(argument)</span></code> is executed in that case.</p> </dd></dl> <dl class="method"> <dt id="mutex.mutex.unlock"> <code class="descclassname">mutex.</code><code class="descname">unlock</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mutex.mutex.unlock" title="Permalink to this definition">¶</a></dt> <dd><p>Unlock the mutex if queue is empty, otherwise execute the first element in the queue.</p> </dd></dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">8.9. <code class="docutils literal notranslate"><span class="pre">mutex</span></code> — Mutual exclusion support</a><ul> <li><a class="reference internal" href="#mutex-objects">8.9.1. Mutex Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="sched.html" title="previous chapter">8.8. <code class="docutils literal notranslate"><span class="pre">sched</span></code> — Event scheduler</a></p> <h4>Next topic</h4> <p class="topless"><a href="queue.html" title="next chapter">8.10. <code class="docutils literal notranslate"><span class="pre">Queue</span></code> — A synchronized queue class</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/library/mutex.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="queue.html" title="8.10. 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