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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>Initialization, Finalization, and Threads — Python 2.7.18 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/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 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="Memory Management" href="memory.html" /> <link rel="prev" title="Code Objects" href="code.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/c-api/init.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/c-api/init.html"> Python documentation for the Python3 version packaged in this release</a>. </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" 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="memory.html" title="Memory Management" accesskey="N">next</a> |</li> <li class="right" > <a href="code.html" title="Code Objects" 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 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Python/C API Reference Manual</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="initialization-finalization-and-threads"> <span id="initialization"></span><h1>Initialization, Finalization, and Threads<a class="headerlink" href="#initialization-finalization-and-threads" title="Permalink to this headline">¶</a></h1> <div class="section" id="initializing-and-finalizing-the-interpreter"> <h2>Initializing and finalizing the interpreter<a class="headerlink" href="#initializing-and-finalizing-the-interpreter" title="Permalink to this headline">¶</a></h2> <dl class="function"> <dt id="c.Py_Initialize"> void <code class="descname">Py_Initialize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_Initialize" title="Permalink to this definition">¶</a></dt> <dd><p id="index-0">Initialize the Python interpreter. In an application embedding Python, this should be called before using any other Python/C API functions; with the exception of <a class="reference internal" href="#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a>, <a class="reference internal" href="#c.Py_SetPythonHome" title="Py_SetPythonHome"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetPythonHome()</span></code></a>, <a class="reference internal" href="#c.PyEval_InitThreads" title="PyEval_InitThreads"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_InitThreads()</span></code></a>, <a class="reference internal" href="#c.PyEval_ReleaseLock" title="PyEval_ReleaseLock"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_ReleaseLock()</span></code></a>, and <a class="reference internal" href="#c.PyEval_AcquireLock" title="PyEval_AcquireLock"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_AcquireLock()</span></code></a>. This initializes the table of loaded modules (<code class="docutils literal notranslate"><span class="pre">sys.modules</span></code>), and creates the fundamental modules <a class="reference internal" href="../library/__builtin__.html#module-__builtin__" title="__builtin__: The module that provides the built-in namespace."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__builtin__</span></code></a>, <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__main__</span></code></a> and <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a>. It also initializes the module search path (<code class="docutils literal notranslate"><span class="pre">sys.path</span></code>). It does not set <code class="docutils literal notranslate"><span class="pre">sys.argv</span></code>; use <a class="reference internal" href="#c.PySys_SetArgvEx" title="PySys_SetArgvEx"><code class="xref c c-func docutils literal notranslate"><span class="pre">PySys_SetArgvEx()</span></code></a> for that. This is a no-op when called for a second time (without calling <a class="reference internal" href="#c.Py_Finalize" title="Py_Finalize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Finalize()</span></code></a> first). There is no return value; it is a fatal error if the initialization fails.</p> </dd></dl> <dl class="function"> <dt id="c.Py_InitializeEx"> void <code class="descname">Py_InitializeEx</code><span class="sig-paren">(</span>int<em> initsigs</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_InitializeEx" title="Permalink to this definition">¶</a></dt> <dd><p>This function works like <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a> if <em>initsigs</em> is <code class="docutils literal notranslate"><span class="pre">1</span></code>. If <em>initsigs</em> is <code class="docutils literal notranslate"><span class="pre">0</span></code>, it skips initialization registration of signal handlers, which might be useful when Python is embedded.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.4.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.Py_IsInitialized"> int <code class="descname">Py_IsInitialized</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_IsInitialized" title="Permalink to this definition">¶</a></dt> <dd><p>Return true (nonzero) when the Python interpreter has been initialized, false (zero) if not. After <a class="reference internal" href="#c.Py_Finalize" title="Py_Finalize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Finalize()</span></code></a> is called, this returns false until <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a> is called again.</p> </dd></dl> <dl class="function"> <dt id="c.Py_Finalize"> void <code class="descname">Py_Finalize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_Finalize" title="Permalink to this definition">¶</a></dt> <dd><p>Undo all initializations made by <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a> and subsequent use of Python/C API functions, and destroy all sub-interpreters (see <a class="reference internal" href="#c.Py_NewInterpreter" title="Py_NewInterpreter"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_NewInterpreter()</span></code></a> below) that were created and not yet destroyed since the last call to <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>. Ideally, this frees all memory allocated by the Python interpreter. This is a no-op when called for a second time (without calling <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a> again first). There is no return value; errors during finalization are ignored.</p> <p>This function is provided for a number of reasons. An embedding application might want to restart Python without having to restart the application itself. An application that has loaded the Python interpreter from a dynamically loadable library (or DLL) might want to free all memory allocated by Python before unloading the DLL. During a hunt for memory leaks in an application a developer might want to free all memory allocated by Python before exiting from the application.</p> <p><strong>Bugs and caveats:</strong> The destruction of modules and objects in modules is done in random order; this may cause destructors (<a class="reference internal" href="../reference/datamodel.html#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__del__()</span></code></a> methods) to fail when they depend on other objects (even functions) or modules. Dynamically loaded extension modules loaded by Python are not unloaded. Small amounts of memory allocated by the Python interpreter may not be freed (if you find a leak, please report it). Memory tied up in circular references between objects is not freed. Some memory allocated by extension modules may not be freed. Some extensions may not work properly if their initialization routine is called more than once; this can happen if an application calls <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a> and <a class="reference internal" href="#c.Py_Finalize" title="Py_Finalize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Finalize()</span></code></a> more than once.</p> </dd></dl> </div> <div class="section" id="process-wide-parameters"> <h2>Process-wide parameters<a class="headerlink" href="#process-wide-parameters" title="Permalink to this headline">¶</a></h2> <dl class="function"> <dt id="c.Py_SetProgramName"> void <code class="descname">Py_SetProgramName</code><span class="sig-paren">(</span>char<em> *name</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_SetProgramName" title="Permalink to this definition">¶</a></dt> <dd><p id="index-1">This function should be called before <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a> is called for the first time, if it is called at all. It tells the interpreter the value of the <code class="docutils literal notranslate"><span class="pre">argv[0]</span></code> argument to the <code class="xref c c-func docutils literal notranslate"><span class="pre">main()</span></code> function of the program. This is used by <a class="reference internal" href="#c.Py_GetPath" title="Py_GetPath"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_GetPath()</span></code></a> and some other functions below to find the Python run-time libraries relative to the interpreter executable. The default value is <code class="docutils literal notranslate"><span class="pre">'python'</span></code>. The argument should point to a zero-terminated character string in static storage whose contents will not change for the duration of the program’s execution. No code in the Python interpreter will change the contents of this storage.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetProgramName"> char* <code class="descname">Py_GetProgramName</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetProgramName" title="Permalink to this definition">¶</a></dt> <dd><p id="index-2">Return the program name set with <a class="reference internal" href="#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a>, or the default. The returned string points into static storage; the caller should not modify its value.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetPrefix"> char* <code class="descname">Py_GetPrefix</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetPrefix" title="Permalink to this definition">¶</a></dt> <dd><p>Return the <em>prefix</em> for installed platform-independent files. This is derived through a number of complicated rules from the program name set with <a class="reference internal" href="#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a> and some environment variables; for example, if the program name is <code class="docutils literal notranslate"><span class="pre">'/usr/local/bin/python'</span></code>, the prefix is <code class="docutils literal notranslate"><span class="pre">'/usr/local'</span></code>. The returned string points into static storage; the caller should not modify its value. This corresponds to the <strong class="makevar">prefix</strong> variable in the top-level <code class="file docutils literal notranslate"><span class="pre">Makefile</span></code> and the <code class="docutils literal notranslate"><span class="pre">--prefix</span></code> argument to the <strong class="program">configure</strong> script at build time. The value is available to Python code as <code class="docutils literal notranslate"><span class="pre">sys.prefix</span></code>. It is only useful on Unix. See also the next function.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetExecPrefix"> char* <code class="descname">Py_GetExecPrefix</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetExecPrefix" title="Permalink to this definition">¶</a></dt> <dd><p>Return the <em>exec-prefix</em> for installed platform-<em>dependent</em> files. This is derived through a number of complicated rules from the program name set with <a class="reference internal" href="#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a> and some environment variables; for example, if the program name is <code class="docutils literal notranslate"><span class="pre">'/usr/local/bin/python'</span></code>, the exec-prefix is <code class="docutils literal notranslate"><span class="pre">'/usr/local'</span></code>. The returned string points into static storage; the caller should not modify its value. This corresponds to the <strong class="makevar">exec_prefix</strong> variable in the top-level <code class="file docutils literal notranslate"><span class="pre">Makefile</span></code> and the <code class="docutils literal notranslate"><span class="pre">--exec-prefix</span></code> argument to the <strong class="program">configure</strong> script at build time. The value is available to Python code as <code class="docutils literal notranslate"><span class="pre">sys.exec_prefix</span></code>. It is only useful on Unix.</p> <p>Background: The exec-prefix differs from the prefix when platform dependent files (such as executables and shared libraries) are installed in a different directory tree. In a typical installation, platform dependent files may be installed in the <code class="file docutils literal notranslate"><span class="pre">/usr/local/plat</span></code> subtree while platform independent may be installed in <code class="file docutils literal notranslate"><span class="pre">/usr/local</span></code>.</p> <p>Generally speaking, a platform is a combination of hardware and software families, e.g. Sparc machines running the Solaris 2.x operating system are considered the same platform, but Intel machines running Solaris 2.x are another platform, and Intel machines running Linux are yet another platform. Different major revisions of the same operating system generally also form different platforms. Non-Unix operating systems are a different story; the installation strategies on those systems are so different that the prefix and exec-prefix are meaningless, and set to the empty string. Note that compiled Python bytecode files are platform independent (but not independent from the Python version by which they were compiled!).</p> <p>System administrators will know how to configure the <strong class="program">mount</strong> or <strong class="program">automount</strong> programs to share <code class="file docutils literal notranslate"><span class="pre">/usr/local</span></code> between platforms while having <code class="file docutils literal notranslate"><span class="pre">/usr/local/plat</span></code> be a different filesystem for each platform.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetProgramFullPath"> char* <code class="descname">Py_GetProgramFullPath</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetProgramFullPath" title="Permalink to this definition">¶</a></dt> <dd><p id="index-3">Return the full program name of the Python executable; this is computed as a side-effect of deriving the default module search path from the program name (set by <a class="reference internal" href="#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a> above). The returned string points into static storage; the caller should not modify its value. The value is available to Python code as <code class="docutils literal notranslate"><span class="pre">sys.executable</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetPath"> char* <code class="descname">Py_GetPath</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetPath" title="Permalink to this definition">¶</a></dt> <dd><p id="index-4">Return the default module search path; this is computed from the program name (set by <a class="reference internal" href="#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a> above) and some environment variables. The returned string consists of a series of directory names separated by a platform dependent delimiter character. The delimiter character is <code class="docutils literal notranslate"><span class="pre">':'</span></code> on Unix and Mac OS X, <code class="docutils literal notranslate"><span class="pre">';'</span></code> on Windows. The returned string points into static storage; the caller should not modify its value. The list <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a> is initialized with this value on interpreter startup; it can be (and usually is) modified later to change the search path for loading modules.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetVersion"> const char* <code class="descname">Py_GetVersion</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetVersion" title="Permalink to this definition">¶</a></dt> <dd><p>Return the version of this Python interpreter. This is a string that looks something like</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="s">"1.5 (#67, Dec 31 1997, 22:34:28) [GCC 2.7.2.2]"</span> </pre></div> </div> <p id="index-5">The first word (up to the first space character) is the current Python version; the first three characters are the major and minor version separated by a period. The returned string points into static storage; the caller should not modify its value. The value is available to Python code as <code class="docutils literal notranslate"><span class="pre">sys.version</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetPlatform"> const char* <code class="descname">Py_GetPlatform</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetPlatform" title="Permalink to this definition">¶</a></dt> <dd><p id="index-6">Return the platform identifier for the current platform. On Unix, this is formed from the “official” name of the operating system, converted to lower case, followed by the major revision number; e.g., for Solaris 2.x, which is also known as SunOS 5.x, the value is <code class="docutils literal notranslate"><span class="pre">'sunos5'</span></code>. On Mac OS X, it is <code class="docutils literal notranslate"><span class="pre">'darwin'</span></code>. On Windows, it is <code class="docutils literal notranslate"><span class="pre">'win'</span></code>. The returned string points into static storage; the caller should not modify its value. The value is available to Python code as <code class="docutils literal notranslate"><span class="pre">sys.platform</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetCopyright"> const char* <code class="descname">Py_GetCopyright</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetCopyright" title="Permalink to this definition">¶</a></dt> <dd><p>Return the official copyright string for the current Python version, for example</p> <p><code class="docutils literal notranslate"><span class="pre">'Copyright</span> <span class="pre">1991-1995</span> <span class="pre">Stichting</span> <span class="pre">Mathematisch</span> <span class="pre">Centrum,</span> <span class="pre">Amsterdam'</span></code></p> <p id="index-7">The returned string points into static storage; the caller should not modify its value. The value is available to Python code as <code class="docutils literal notranslate"><span class="pre">sys.copyright</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetCompiler"> const char* <code class="descname">Py_GetCompiler</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetCompiler" title="Permalink to this definition">¶</a></dt> <dd><p>Return an indication of the compiler used to build the current Python version, in square brackets, for example:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="s">"[GCC 2.7.2.2]"</span> </pre></div> </div> <p id="index-8">The returned string points into static storage; the caller should not modify its value. The value is available to Python code as part of the variable <code class="docutils literal notranslate"><span class="pre">sys.version</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetBuildInfo"> const char* <code class="descname">Py_GetBuildInfo</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetBuildInfo" title="Permalink to this definition">¶</a></dt> <dd><p>Return information about the sequence number and build date and time of the current Python interpreter instance, for example</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="s">"#67, Aug 1 1997, 22:34:28"</span> </pre></div> </div> <p id="index-9">The returned string points into static storage; the caller should not modify its value. The value is available to Python code as part of the variable <code class="docutils literal notranslate"><span class="pre">sys.version</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.PySys_SetArgvEx"> void <code class="descname">PySys_SetArgvEx</code><span class="sig-paren">(</span>int<em> argc</em>, char<em> **argv</em>, int<em> updatepath</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PySys_SetArgvEx" title="Permalink to this definition">¶</a></dt> <dd><p id="index-10">Set <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.argv</span></code></a> based on <em>argc</em> and <em>argv</em>. These parameters are similar to those passed to the program’s <code class="xref c c-func docutils literal notranslate"><span class="pre">main()</span></code> function with the difference that the first entry should refer to the script file to be executed rather than the executable hosting the Python interpreter. If there isn’t a script that will be run, the first entry in <em>argv</em> can be an empty string. If this function fails to initialize <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.argv</span></code></a>, a fatal condition is signalled using <a class="reference internal" href="sys.html#c.Py_FatalError" title="Py_FatalError"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_FatalError()</span></code></a>.</p> <p>If <em>updatepath</em> is zero, this is all the function does. If <em>updatepath</em> is non-zero, the function also modifies <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a> according to the following algorithm:</p> <ul class="simple"> <li>If the name of an existing script is passed in <code class="docutils literal notranslate"><span class="pre">argv[0]</span></code>, the absolute path of the directory where the script is located is prepended to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a>.</li> <li>Otherwise (that is, if <em>argc</em> is 0 or <code class="docutils literal notranslate"><span class="pre">argv[0]</span></code> doesn’t point to an existing file name), an empty string is prepended to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a>, which is the same as prepending the current working directory (<code class="docutils literal notranslate"><span class="pre">"."</span></code>).</li> </ul> <div class="admonition note"> <p class="first admonition-title">Note</p> <p>It is recommended that applications embedding the Python interpreter for purposes other than executing a single script pass <code class="docutils literal notranslate"><span class="pre">0</span></code> as <em>updatepath</em>, and update <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a> themselves if desired. See <a class="reference external" href="https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983">CVE-2008-5983</a>.</p> <p>On versions before 2.6.6, you can achieve the same effect by manually popping the first <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a> element after having called <a class="reference internal" href="#c.PySys_SetArgv" title="PySys_SetArgv"><code class="xref c c-func docutils literal notranslate"><span class="pre">PySys_SetArgv()</span></code></a>, for example using:</p> <div class="last highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyRun_SimpleString</span><span class="p">(</span><span class="s">"import sys; sys.path.pop(0)</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> </pre></div> </div> </div> <div class="versionadded"> <p><span class="versionmodified">New in version 2.6.6.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PySys_SetArgv"> void <code class="descname">PySys_SetArgv</code><span class="sig-paren">(</span>int<em> argc</em>, char<em> **argv</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PySys_SetArgv" title="Permalink to this definition">¶</a></dt> <dd><p>This function works like <a class="reference internal" href="#c.PySys_SetArgvEx" title="PySys_SetArgvEx"><code class="xref c c-func docutils literal notranslate"><span class="pre">PySys_SetArgvEx()</span></code></a> with <em>updatepath</em> set to <code class="docutils literal notranslate"><span class="pre">1</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.Py_SetPythonHome"> void <code class="descname">Py_SetPythonHome</code><span class="sig-paren">(</span>char<em> *home</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_SetPythonHome" title="Permalink to this definition">¶</a></dt> <dd><p>Set the default “home” directory, that is, the location of the standard Python libraries. See <span class="target" id="index-11"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONHOME</span></code></a> for the meaning of the argument string.</p> <p>The argument should point to a zero-terminated character string in static storage whose contents will not change for the duration of the program’s execution. No code in the Python interpreter will change the contents of this storage.</p> </dd></dl> <dl class="function"> <dt id="c.Py_GetPythonHome"> char* <code class="descname">Py_GetPythonHome</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GetPythonHome" title="Permalink to this definition">¶</a></dt> <dd><p>Return the default “home”, that is, the value set by a previous call to <a class="reference internal" href="#c.Py_SetPythonHome" title="Py_SetPythonHome"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetPythonHome()</span></code></a>, or the value of the <span class="target" id="index-12"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONHOME</span></code></a> environment variable if it is set.</p> </dd></dl> </div> <div class="section" id="thread-state-and-the-global-interpreter-lock"> <span id="threads"></span><h2>Thread State and the Global Interpreter Lock<a class="headerlink" href="#thread-state-and-the-global-interpreter-lock" title="Permalink to this headline">¶</a></h2> <p id="index-13">The Python interpreter is not fully thread-safe. In order to support multi-threaded Python programs, there’s a global lock, called the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">global interpreter lock</span></a> or <a class="reference internal" href="../glossary.html#term-gil"><span class="xref std std-term">GIL</span></a>, that must be held by the current thread before it can safely access Python objects. Without the lock, even the simplest operations could cause problems in a multi-threaded program: for example, when two threads simultaneously increment the reference count of the same object, the reference count could end up being incremented only once instead of twice.</p> <p id="index-14">Therefore, the rule exists that only the thread that has acquired the <a class="reference internal" href="../glossary.html#term-gil"><span class="xref std std-term">GIL</span></a> may operate on Python objects or call Python/C API functions. In order to emulate concurrency of execution, the interpreter regularly tries to switch threads (see <a class="reference internal" href="../library/sys.html#sys.setcheckinterval" title="sys.setcheckinterval"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.setcheckinterval()</span></code></a>). The lock is also released around potentially blocking I/O operations like reading or writing a file, so that other Python threads can run in the meantime.</p> <p id="index-15">The Python interpreter keeps some thread-specific bookkeeping information inside a data structure called <a class="reference internal" href="#c.PyThreadState" title="PyThreadState"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyThreadState</span></code></a>. There’s also one global variable pointing to the current <a class="reference internal" href="#c.PyThreadState" title="PyThreadState"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyThreadState</span></code></a>: it can be retrieved using <a class="reference internal" href="#c.PyThreadState_Get" title="PyThreadState_Get"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThreadState_Get()</span></code></a>.</p> <div class="section" id="releasing-the-gil-from-extension-code"> <h3>Releasing the GIL from extension code<a class="headerlink" href="#releasing-the-gil-from-extension-code" title="Permalink to this headline">¶</a></h3> <p>Most extension code manipulating the <a class="reference internal" href="../glossary.html#term-gil"><span class="xref std std-term">GIL</span></a> has the following simple structure:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">Save</span> <span class="n">the</span> <span class="kr">thread</span> <span class="n">state</span> <span class="n">in</span> <span class="n">a</span> <span class="n">local</span> <span class="n">variable</span><span class="p">.</span> <span class="n">Release</span> <span class="n">the</span> <span class="n">global</span> <span class="n">interpreter</span> <span class="n">lock</span><span class="p">.</span> <span class="p">...</span> <span class="n">Do</span> <span class="n">some</span> <span class="n">blocking</span> <span class="n">I</span><span class="o">/</span><span class="n">O</span> <span class="n">operation</span> <span class="p">...</span> <span class="n">Reacquire</span> <span class="n">the</span> <span class="n">global</span> <span class="n">interpreter</span> <span class="n">lock</span><span class="p">.</span> <span class="n">Restore</span> <span class="n">the</span> <span class="kr">thread</span> <span class="n">state</span> <span class="n">from</span> <span class="n">the</span> <span class="n">local</span> <span class="n">variable</span><span class="p">.</span> </pre></div> </div> <p>This is so common that a pair of macros exists to simplify it:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">Py_BEGIN_ALLOW_THREADS</span> <span class="p">...</span> <span class="n">Do</span> <span class="n">some</span> <span class="n">blocking</span> <span class="n">I</span><span class="o">/</span><span class="n">O</span> <span class="n">operation</span> <span class="p">...</span> <span class="n">Py_END_ALLOW_THREADS</span> </pre></div> </div> <p id="index-16">The <a class="reference internal" href="#c.Py_BEGIN_ALLOW_THREADS" title="Py_BEGIN_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_BEGIN_ALLOW_THREADS</span></code></a> macro opens a new block and declares a hidden local variable; the <a class="reference internal" href="#c.Py_END_ALLOW_THREADS" title="Py_END_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_END_ALLOW_THREADS</span></code></a> macro closes the block. These two macros are still available when Python is compiled without thread support (they simply have an empty expansion).</p> <p>When thread support is enabled, the block above expands to the following code:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyThreadState</span> <span class="o">*</span><span class="n">_save</span><span class="p">;</span> <span class="n">_save</span> <span class="o">=</span> <span class="n">PyEval_SaveThread</span><span class="p">();</span> <span class="p">...</span><span class="n">Do</span> <span class="n">some</span> <span class="n">blocking</span> <span class="n">I</span><span class="o">/</span><span class="n">O</span> <span class="n">operation</span><span class="p">...</span> <span class="n">PyEval_RestoreThread</span><span class="p">(</span><span class="n">_save</span><span class="p">);</span> </pre></div> </div> <p id="index-17">Here is how these functions work: the global interpreter lock is used to protect the pointer to the current thread state. When releasing the lock and saving the thread state, the current thread state pointer must be retrieved before the lock is released (since another thread could immediately acquire the lock and store its own thread state in the global variable). Conversely, when acquiring the lock and restoring the thread state, the lock must be acquired before storing the thread state pointer.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Calling system I/O functions is the most common use case for releasing the GIL, but it can also be useful before calling long-running computations which don’t need access to Python objects, such as compression or cryptographic functions operating over memory buffers. For example, the standard <a class="reference internal" href="../library/zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zlib</span></code></a> and <a class="reference internal" href="../library/hashlib.html#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal notranslate"><span class="pre">hashlib</span></code></a> modules release the GIL when compressing or hashing data.</p> </div> </div> <div class="section" id="non-python-created-threads"> <span id="gilstate"></span><h3>Non-Python created threads<a class="headerlink" href="#non-python-created-threads" title="Permalink to this headline">¶</a></h3> <p>When threads are created using the dedicated Python APIs (such as the <a class="reference internal" href="../library/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> module), a thread state is automatically associated to them and the code showed above is therefore correct. However, when threads are created from C (for example by a third-party library with its own thread management), they don’t hold the GIL, nor is there a thread state structure for them.</p> <p>If you need to call Python code from these threads (often this will be part of a callback API provided by the aforementioned third-party library), you must first register these threads with the interpreter by creating a thread state data structure, then acquiring the GIL, and finally storing their thread state pointer, before you can start using the Python/C API. When you are done, you should reset the thread state pointer, release the GIL, and finally free the thread state data structure.</p> <p>The <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> and <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a> functions do all of the above automatically. The typical idiom for calling into Python from a C thread is:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyGILState_STATE</span> <span class="n">gstate</span><span class="p">;</span> <span class="n">gstate</span> <span class="o">=</span> <span class="n">PyGILState_Ensure</span><span class="p">();</span> <span class="cm">/* Perform Python actions here. */</span> <span class="n">result</span> <span class="o">=</span> <span class="n">CallSomeFunction</span><span class="p">();</span> <span class="cm">/* evaluate result or handle exception */</span> <span class="cm">/* Release the thread. No Python API allowed beyond this point. */</span> <span class="n">PyGILState_Release</span><span class="p">(</span><span class="n">gstate</span><span class="p">);</span> </pre></div> </div> <p>Note that the <code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_*()</span></code> functions assume there is only one global interpreter (created automatically by <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>). Python supports the creation of additional interpreters (using <a class="reference internal" href="#c.Py_NewInterpreter" title="Py_NewInterpreter"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_NewInterpreter()</span></code></a>), but mixing multiple interpreters and the <code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_*()</span></code> API is unsupported.</p> <p>Another important thing to note about threads is their behaviour in the face of the C <code class="xref c c-func docutils literal notranslate"><span class="pre">fork()</span></code> call. On most systems with <code class="xref c c-func docutils literal notranslate"><span class="pre">fork()</span></code>, after a process forks only the thread that issued the fork will exist. That also means any locks held by other threads will never be released. Python solves this for <a class="reference internal" href="../library/os.html#os.fork" title="os.fork"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.fork()</span></code></a> by acquiring the locks it uses internally before the fork, and releasing them afterwards. In addition, it resets any <a class="reference internal" href="../library/threading.html#lock-objects"><span class="std std-ref">Lock Objects</span></a> in the child. When extending or embedding Python, there is no way to inform Python of additional (non-Python) locks that need to be acquired before or reset after a fork. OS facilities such as <code class="xref c c-func docutils literal notranslate"><span class="pre">pthread_atfork()</span></code> would need to be used to accomplish the same thing. Additionally, when extending or embedding Python, calling <code class="xref c c-func docutils literal notranslate"><span class="pre">fork()</span></code> directly rather than through <a class="reference internal" href="../library/os.html#os.fork" title="os.fork"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.fork()</span></code></a> (and returning to or calling into Python) may result in a deadlock by one of Python’s internal locks being held by a thread that is defunct after the fork. <a class="reference internal" href="sys.html#c.PyOS_AfterFork" title="PyOS_AfterFork"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_AfterFork()</span></code></a> tries to reset the necessary locks, but is not always able to.</p> </div> <div class="section" id="high-level-api"> <h3>High-level API<a class="headerlink" href="#high-level-api" title="Permalink to this headline">¶</a></h3> <p>These are the most commonly used types and functions when writing C extension code, or when embedding the Python interpreter:</p> <dl class="type"> <dt id="c.PyInterpreterState"> <code class="descname">PyInterpreterState</code><a class="headerlink" href="#c.PyInterpreterState" title="Permalink to this definition">¶</a></dt> <dd><p>This data structure represents the state shared by a number of cooperating threads. Threads belonging to the same interpreter share their module administration and a few other internal items. There are no public members in this structure.</p> <p>Threads belonging to different interpreters initially share nothing, except process state like available memory, open file descriptors and such. The global interpreter lock is also shared by all threads, regardless of to which interpreter they belong.</p> </dd></dl> <dl class="type"> <dt id="c.PyThreadState"> <code class="descname">PyThreadState</code><a class="headerlink" href="#c.PyThreadState" title="Permalink to this definition">¶</a></dt> <dd><p>This data structure represents the state of a single thread. The only public data member is <a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyInterpreterState</span> <span class="pre">*</span></code></a><code class="xref py py-attr docutils literal notranslate"><span class="pre">interp</span></code>, which points to this thread’s interpreter state.</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_InitThreads"> void <code class="descname">PyEval_InitThreads</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_InitThreads" title="Permalink to this definition">¶</a></dt> <dd><p id="index-18">Initialize and acquire the global interpreter lock. It should be called in the main thread before creating a second thread or engaging in any other thread operations such as <a class="reference internal" href="#c.PyEval_ReleaseLock" title="PyEval_ReleaseLock"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_ReleaseLock()</span></code></a> or <code class="docutils literal notranslate"><span class="pre">PyEval_ReleaseThread(tstate)</span></code>. It is not needed before calling <a class="reference internal" href="#c.PyEval_SaveThread" title="PyEval_SaveThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SaveThread()</span></code></a> or <a class="reference internal" href="#c.PyEval_RestoreThread" title="PyEval_RestoreThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_RestoreThread()</span></code></a>.</p> <p id="index-19">This is a no-op when called for a second time. It is safe to call this function before calling <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>.</p> <div class="admonition note" id="index-20"> <p class="first admonition-title">Note</p> <p>When only the main thread exists, no GIL operations are needed. This is a common situation (most Python programs do not use threads), and the lock operations slow the interpreter down a bit. Therefore, the lock is not created initially. This situation is equivalent to having acquired the lock: when there is only a single thread, all object accesses are safe. Therefore, when this function initializes the global interpreter lock, it also acquires it. Before the Python <code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code> module creates a new thread, knowing that either it has the lock or the lock hasn’t been created yet, it calls <a class="reference internal" href="#c.PyEval_InitThreads" title="PyEval_InitThreads"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_InitThreads()</span></code></a>. When this call returns, it is guaranteed that the lock has been created and that the calling thread has acquired it.</p> <p>It is <strong>not</strong> safe to call this function when it is unknown which thread (if any) currently has the global interpreter lock.</p> <p class="last">This function is not available when thread support is disabled at compile time.</p> </div> </dd></dl> <dl class="function"> <dt id="c.PyEval_ThreadsInitialized"> int <code class="descname">PyEval_ThreadsInitialized</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_ThreadsInitialized" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a non-zero value if <a class="reference internal" href="#c.PyEval_InitThreads" title="PyEval_InitThreads"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_InitThreads()</span></code></a> has been called. This function can be called without holding the GIL, and therefore can be used to avoid calls to the locking API when running single-threaded. This function is not available when thread support is disabled at compile time.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.4.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyEval_SaveThread"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">PyEval_SaveThread</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_SaveThread" title="Permalink to this definition">¶</a></dt> <dd><p>Release the global interpreter lock (if it has been created and thread support is enabled) and reset the thread state to <em>NULL</em>, returning the previous thread state (which is not <em>NULL</em>). If the lock has been created, the current thread must have acquired it. (This function is available even when thread support is disabled at compile time.)</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_RestoreThread"> void <code class="descname">PyEval_RestoreThread</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_RestoreThread" title="Permalink to this definition">¶</a></dt> <dd><p>Acquire the global interpreter lock (if it has been created and thread support is enabled) and set the thread state to <em>tstate</em>, which must not be <em>NULL</em>. If the lock has been created, the current thread must not have acquired it, otherwise deadlock ensues. (This function is available even when thread support is disabled at compile time.)</p> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_Get"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">PyThreadState_Get</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_Get" title="Permalink to this definition">¶</a></dt> <dd><p>Return the current thread state. The global interpreter lock must be held. When the current thread state is <em>NULL</em>, this issues a fatal error (so that the caller needn’t check for <em>NULL</em>).</p> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_Swap"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">PyThreadState_Swap</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_Swap" title="Permalink to this definition">¶</a></dt> <dd><p>Swap the current thread state with the thread state given by the argument <em>tstate</em>, which may be <em>NULL</em>. The global interpreter lock must be held and is not released.</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_ReInitThreads"> void <code class="descname">PyEval_ReInitThreads</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_ReInitThreads" title="Permalink to this definition">¶</a></dt> <dd><p>This function is called from <a class="reference internal" href="sys.html#c.PyOS_AfterFork" title="PyOS_AfterFork"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_AfterFork()</span></code></a> to ensure that newly created child processes don’t hold locks referring to threads which are not running in the child process.</p> </dd></dl> <p>The following functions use thread-local storage, and are not compatible with sub-interpreters:</p> <dl class="function"> <dt id="c.PyGILState_Ensure"> PyGILState_STATE <code class="descname">PyGILState_Ensure</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyGILState_Ensure" title="Permalink to this definition">¶</a></dt> <dd><p>Ensure that the current thread is ready to call the Python C API regardless of the current state of Python, or of the global interpreter lock. This may be called as many times as desired by a thread as long as each call is matched with a call to <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a>. In general, other thread-related APIs may be used between <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> and <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a> calls as long as the thread state is restored to its previous state before the Release(). For example, normal usage of the <a class="reference internal" href="#c.Py_BEGIN_ALLOW_THREADS" title="Py_BEGIN_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_BEGIN_ALLOW_THREADS</span></code></a> and <a class="reference internal" href="#c.Py_END_ALLOW_THREADS" title="Py_END_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_END_ALLOW_THREADS</span></code></a> macros is acceptable.</p> <p>The return value is an opaque “handle” to the thread state when <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> was called, and must be passed to <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a> to ensure Python is left in the same state. Even though recursive calls are allowed, these handles <em>cannot</em> be shared - each unique call to <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> must save the handle for its call to <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a>.</p> <p>When the function returns, the current thread will hold the GIL and be able to call arbitrary Python code. Failure is a fatal error.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.3.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyGILState_Release"> void <code class="descname">PyGILState_Release</code><span class="sig-paren">(</span>PyGILState_STATE<span class="sig-paren">)</span><a class="headerlink" href="#c.PyGILState_Release" title="Permalink to this definition">¶</a></dt> <dd><p>Release any resources previously acquired. After this call, Python’s state will be the same as it was prior to the corresponding <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> call (but generally this state will be unknown to the caller, hence the use of the GILState API).</p> <p>Every call to <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> must be matched by a call to <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a> on the same thread.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.3.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyGILState_GetThisThreadState"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">PyGILState_GetThisThreadState</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyGILState_GetThisThreadState" title="Permalink to this definition">¶</a></dt> <dd><p>Get the current thread state for this thread. May return <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if no GILState API has been used on the current thread. Note that the main thread always has such a thread-state, even if no auto-thread-state call has been made on the main thread. This is mainly a helper/diagnostic function.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.3.</span></p> </div> </dd></dl> <p>The following macros are normally used without a trailing semicolon; look for example usage in the Python source distribution.</p> <dl class="macro"> <dt id="c.Py_BEGIN_ALLOW_THREADS"> <code class="descname">Py_BEGIN_ALLOW_THREADS</code><a class="headerlink" href="#c.Py_BEGIN_ALLOW_THREADS" title="Permalink to this definition">¶</a></dt> <dd><p>This macro expands to <code class="docutils literal notranslate"><span class="pre">{</span> <span class="pre">PyThreadState</span> <span class="pre">*_save;</span> <span class="pre">_save</span> <span class="pre">=</span> <span class="pre">PyEval_SaveThread();</span></code>. Note that it contains an opening brace; it must be matched with a following <a class="reference internal" href="#c.Py_END_ALLOW_THREADS" title="Py_END_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_END_ALLOW_THREADS</span></code></a> macro. See above for further discussion of this macro. It is a no-op when thread support is disabled at compile time.</p> </dd></dl> <dl class="macro"> <dt id="c.Py_END_ALLOW_THREADS"> <code class="descname">Py_END_ALLOW_THREADS</code><a class="headerlink" href="#c.Py_END_ALLOW_THREADS" title="Permalink to this definition">¶</a></dt> <dd><p>This macro expands to <code class="docutils literal notranslate"><span class="pre">PyEval_RestoreThread(_save);</span> <span class="pre">}</span></code>. Note that it contains a closing brace; it must be matched with an earlier <a class="reference internal" href="#c.Py_BEGIN_ALLOW_THREADS" title="Py_BEGIN_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_BEGIN_ALLOW_THREADS</span></code></a> macro. See above for further discussion of this macro. It is a no-op when thread support is disabled at compile time.</p> </dd></dl> <dl class="macro"> <dt id="c.Py_BLOCK_THREADS"> <code class="descname">Py_BLOCK_THREADS</code><a class="headerlink" href="#c.Py_BLOCK_THREADS" title="Permalink to this definition">¶</a></dt> <dd><p>This macro expands to <code class="docutils literal notranslate"><span class="pre">PyEval_RestoreThread(_save);</span></code>: it is equivalent to <a class="reference internal" href="#c.Py_END_ALLOW_THREADS" title="Py_END_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_END_ALLOW_THREADS</span></code></a> without the closing brace. It is a no-op when thread support is disabled at compile time.</p> </dd></dl> <dl class="macro"> <dt id="c.Py_UNBLOCK_THREADS"> <code class="descname">Py_UNBLOCK_THREADS</code><a class="headerlink" href="#c.Py_UNBLOCK_THREADS" title="Permalink to this definition">¶</a></dt> <dd><p>This macro expands to <code class="docutils literal notranslate"><span class="pre">_save</span> <span class="pre">=</span> <span class="pre">PyEval_SaveThread();</span></code>: it is equivalent to <a class="reference internal" href="#c.Py_BEGIN_ALLOW_THREADS" title="Py_BEGIN_ALLOW_THREADS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_BEGIN_ALLOW_THREADS</span></code></a> without the opening brace and variable declaration. It is a no-op when thread support is disabled at compile time.</p> </dd></dl> </div> <div class="section" id="low-level-api"> <h3>Low-level API<a class="headerlink" href="#low-level-api" title="Permalink to this headline">¶</a></h3> <p>All of the following functions are only available when thread support is enabled at compile time, and must be called only when the global interpreter lock has been created.</p> <dl class="function"> <dt id="c.PyInterpreterState_New"> <a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a>* <code class="descname">PyInterpreterState_New</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyInterpreterState_New" title="Permalink to this definition">¶</a></dt> <dd><p>Create a new interpreter state object. The global interpreter lock need not be held, but may be held if it is necessary to serialize calls to this function.</p> </dd></dl> <dl class="function"> <dt id="c.PyInterpreterState_Clear"> void <code class="descname">PyInterpreterState_Clear</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a><em> *interp</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyInterpreterState_Clear" title="Permalink to this definition">¶</a></dt> <dd><p>Reset all information in an interpreter state object. The global interpreter lock must be held.</p> </dd></dl> <dl class="function"> <dt id="c.PyInterpreterState_Delete"> void <code class="descname">PyInterpreterState_Delete</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a><em> *interp</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyInterpreterState_Delete" title="Permalink to this definition">¶</a></dt> <dd><p>Destroy an interpreter state object. The global interpreter lock need not be held. The interpreter state must have been reset with a previous call to <a class="reference internal" href="#c.PyInterpreterState_Clear" title="PyInterpreterState_Clear"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyInterpreterState_Clear()</span></code></a>.</p> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_New"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">PyThreadState_New</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a><em> *interp</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_New" title="Permalink to this definition">¶</a></dt> <dd><p>Create a new thread state object belonging to the given interpreter object. The global interpreter lock need not be held, but may be held if it is necessary to serialize calls to this function.</p> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_Clear"> void <code class="descname">PyThreadState_Clear</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_Clear" title="Permalink to this definition">¶</a></dt> <dd><p>Reset all information in a thread state object. The global interpreter lock must be held.</p> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_Delete"> void <code class="descname">PyThreadState_Delete</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_Delete" title="Permalink to this definition">¶</a></dt> <dd><p>Destroy a thread state object. The global interpreter lock need not be held. The thread state must have been reset with a previous call to <a class="reference internal" href="#c.PyThreadState_Clear" title="PyThreadState_Clear"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThreadState_Clear()</span></code></a>.</p> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_GetDict"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyThreadState_GetDict</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_GetDict" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: Borrowed reference.</em><p>Return a dictionary in which extensions can store thread-specific state information. Each extension should use a unique key to use to store state in the dictionary. It is okay to call this function when no current thread state is available. If this function returns <em>NULL</em>, no exception has been raised and the caller should assume no current thread state is available.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 2.3: </span>Previously this could only be called when a current thread is active, and <em>NULL</em> meant that an exception was raised.</p> </div> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_SetAsyncExc"> int <code class="descname">PyThreadState_SetAsyncExc</code><span class="sig-paren">(</span>long<em> id</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *exc</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_SetAsyncExc" title="Permalink to this definition">¶</a></dt> <dd><p>Asynchronously raise an exception in a thread. The <em>id</em> argument is the thread id of the target thread; <em>exc</em> is the exception object to be raised. This function does not steal any references to <em>exc</em>. To prevent naive misuse, you must write your own C extension to call this. Must be called with the GIL held. Returns the number of thread states modified; this is normally one, but will be zero if the thread id isn’t found. If <em>exc</em> is <code class="xref py py-const docutils literal notranslate"><span class="pre">NULL</span></code>, the pending exception (if any) for the thread is cleared. This raises no exceptions.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.3.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyEval_AcquireThread"> void <code class="descname">PyEval_AcquireThread</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_AcquireThread" title="Permalink to this definition">¶</a></dt> <dd><p>Acquire the global interpreter lock and set the current thread state to <em>tstate</em>, which should not be <em>NULL</em>. The lock must have been created earlier. If this thread already has the lock, deadlock ensues.</p> <p><a class="reference internal" href="#c.PyEval_RestoreThread" title="PyEval_RestoreThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_RestoreThread()</span></code></a> is a higher-level function which is always available (even when thread support isn’t enabled or when threads have not been initialized).</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_ReleaseThread"> void <code class="descname">PyEval_ReleaseThread</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_ReleaseThread" title="Permalink to this definition">¶</a></dt> <dd><p>Reset the current thread state to <em>NULL</em> and release the global interpreter lock. The lock must have been created earlier and must be held by the current thread. The <em>tstate</em> argument, which must not be <em>NULL</em>, is only used to check that it represents the current thread state — if it isn’t, a fatal error is reported.</p> <p><a class="reference internal" href="#c.PyEval_SaveThread" title="PyEval_SaveThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SaveThread()</span></code></a> is a higher-level function which is always available (even when thread support isn’t enabled or when threads have not been initialized).</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_AcquireLock"> void <code class="descname">PyEval_AcquireLock</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_AcquireLock" title="Permalink to this definition">¶</a></dt> <dd><p>Acquire the global interpreter lock. The lock must have been created earlier. If this thread already has the lock, a deadlock ensues.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">This function does not change the current thread state. Please use <a class="reference internal" href="#c.PyEval_RestoreThread" title="PyEval_RestoreThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_RestoreThread()</span></code></a> or <a class="reference internal" href="#c.PyEval_AcquireThread" title="PyEval_AcquireThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_AcquireThread()</span></code></a> instead.</p> </div> </dd></dl> <dl class="function"> <dt id="c.PyEval_ReleaseLock"> void <code class="descname">PyEval_ReleaseLock</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_ReleaseLock" title="Permalink to this definition">¶</a></dt> <dd><p>Release the global interpreter lock. The lock must have been created earlier.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">This function does not change the current thread state. Please use <a class="reference internal" href="#c.PyEval_SaveThread" title="PyEval_SaveThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SaveThread()</span></code></a> or <a class="reference internal" href="#c.PyEval_ReleaseThread" title="PyEval_ReleaseThread"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_ReleaseThread()</span></code></a> instead.</p> </div> </dd></dl> </div> </div> <div class="section" id="sub-interpreter-support"> <h2>Sub-interpreter support<a class="headerlink" href="#sub-interpreter-support" title="Permalink to this headline">¶</a></h2> <p>While in most uses, you will only embed a single Python interpreter, there are cases where you need to create several independent interpreters in the same process and perhaps even in the same thread. Sub-interpreters allow you to do that. You can switch between sub-interpreters using the <a class="reference internal" href="#c.PyThreadState_Swap" title="PyThreadState_Swap"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyThreadState_Swap()</span></code></a> function. You can create and destroy them using the following functions:</p> <dl class="function"> <dt id="c.Py_NewInterpreter"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">Py_NewInterpreter</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_NewInterpreter" title="Permalink to this definition">¶</a></dt> <dd><p id="index-21">Create a new sub-interpreter. This is an (almost) totally separate environment for the execution of Python code. In particular, the new interpreter has separate, independent versions of all imported modules, including the fundamental modules <code class="xref py py-mod docutils literal notranslate"><span class="pre">builtins</span></code>, <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__main__</span></code></a> and <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a>. The table of loaded modules (<code class="docutils literal notranslate"><span class="pre">sys.modules</span></code>) and the module search path (<code class="docutils literal notranslate"><span class="pre">sys.path</span></code>) are also separate. The new environment has no <code class="docutils literal notranslate"><span class="pre">sys.argv</span></code> variable. It has new standard I/O stream file objects <code class="docutils literal notranslate"><span class="pre">sys.stdin</span></code>, <code class="docutils literal notranslate"><span class="pre">sys.stdout</span></code> and <code class="docutils literal notranslate"><span class="pre">sys.stderr</span></code> (however these refer to the same underlying file descriptors).</p> <p>The return value points to the first thread state created in the new sub-interpreter. This thread state is made in the current thread state. Note that no actual thread is created; see the discussion of thread states below. If creation of the new interpreter is unsuccessful, <em>NULL</em> is returned; no exception is set since the exception state is stored in the current thread state and there may not be a current thread state. (Like all other Python/C API functions, the global interpreter lock must be held before calling this function and is still held when it returns; however, unlike most other Python/C API functions, there needn’t be a current thread state on entry.)</p> <p id="index-22">Extension modules are shared between (sub-)interpreters as follows: the first time a particular extension is imported, it is initialized normally, and a (shallow) copy of its module’s dictionary is squirreled away. When the same extension is imported by another (sub-)interpreter, a new module is initialized and filled with the contents of this copy; the extension’s <code class="docutils literal notranslate"><span class="pre">init</span></code> function is not called. Note that this is different from what happens when an extension is imported after the interpreter has been completely re-initialized by calling <a class="reference internal" href="#c.Py_Finalize" title="Py_Finalize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Finalize()</span></code></a> and <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>; in that case, the extension’s <code class="docutils literal notranslate"><span class="pre">initmodule</span></code> function <em>is</em> called again.</p> <span class="target" id="index-23"></span></dd></dl> <dl class="function"> <dt id="c.Py_EndInterpreter"> void <code class="descname">Py_EndInterpreter</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_EndInterpreter" title="Permalink to this definition">¶</a></dt> <dd><p id="index-24">Destroy the (sub-)interpreter represented by the given thread state. The given thread state must be the current thread state. See the discussion of thread states below. When the call returns, the current thread state is <em>NULL</em>. All thread states associated with this interpreter are destroyed. (The global interpreter lock must be held before calling this function and is still held when it returns.) <a class="reference internal" href="#c.Py_Finalize" title="Py_Finalize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Finalize()</span></code></a> will destroy all sub-interpreters that haven’t been explicitly destroyed at that point.</p> </dd></dl> <div class="section" id="bugs-and-caveats"> <h3>Bugs and caveats<a class="headerlink" href="#bugs-and-caveats" title="Permalink to this headline">¶</a></h3> <p>Because sub-interpreters (and the main interpreter) are part of the same process, the insulation between them isn’t perfect — for example, using low-level file operations like <a class="reference internal" href="../library/os.html#os.close" title="os.close"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.close()</span></code></a> they can (accidentally or maliciously) affect each other’s open files. Because of the way extensions are shared between (sub-)interpreters, some extensions may not work properly; this is especially likely when the extension makes use of (static) global variables, or when the extension manipulates its module’s dictionary after its initialization. It is possible to insert objects created in one sub-interpreter into a namespace of another sub-interpreter; this should be done with great care to avoid sharing user-defined functions, methods, instances or classes between sub-interpreters, since import operations executed by such objects may affect the wrong (sub-)interpreter’s dictionary of loaded modules.</p> <p>Also note that combining this functionality with <code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_*()</span></code> APIs is delicate, because these APIs assume a bijection between Python thread states and OS-level threads, an assumption broken by the presence of sub-interpreters. It is highly recommended that you don’t switch sub-interpreters between a pair of matching <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Ensure()</span></code></a> and <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyGILState_Release()</span></code></a> calls. Furthermore, extensions (such as <a class="reference internal" href="../library/ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a>) using these APIs to allow calling of Python code from non-Python created threads will probably be broken when using sub-interpreters.</p> </div> </div> <div class="section" id="asynchronous-notifications"> <h2>Asynchronous Notifications<a class="headerlink" href="#asynchronous-notifications" title="Permalink to this headline">¶</a></h2> <p>A mechanism is provided to make asynchronous notifications to the main interpreter thread. These notifications take the form of a function pointer and a void pointer argument.</p> <dl class="function"> <dt id="c.Py_AddPendingCall"> int <code class="descname">Py_AddPendingCall</code><span class="sig-paren">(</span>int (<em>*func</em>)(void *), void<em> *arg</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_AddPendingCall" title="Permalink to this definition">¶</a></dt> <dd><p id="index-25">Schedule a function to be called from the main interpreter thread. On success, <code class="docutils literal notranslate"><span class="pre">0</span></code> is returned and <em>func</em> is queued for being called in the main thread. On failure, <code class="docutils literal notranslate"><span class="pre">-1</span></code> is returned without setting any exception.</p> <p>When successfully queued, <em>func</em> will be <em>eventually</em> called from the main interpreter thread with the argument <em>arg</em>. It will be called asynchronously with respect to normally running Python code, but with both these conditions met:</p> <ul class="simple"> <li>on a <a class="reference internal" href="../glossary.html#term-bytecode"><span class="xref std std-term">bytecode</span></a> boundary;</li> <li>with the main thread holding the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">global interpreter lock</span></a> (<em>func</em> can therefore use the full C API).</li> </ul> <p><em>func</em> must return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, or <code class="docutils literal notranslate"><span class="pre">-1</span></code> on failure with an exception set. <em>func</em> won’t be interrupted to perform another asynchronous notification recursively, but it can still be interrupted to switch threads if the global interpreter lock is released.</p> <p>This function doesn’t need a current thread state to run, and it doesn’t need the global interpreter lock.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">This is a low-level function, only useful for very special cases. There is no guarantee that <em>func</em> will be called as quick as possible. If the main thread is busy executing a system call, <em>func</em> won’t be called before the system call returns. This function is generally <strong>not</strong> suitable for calling Python code from arbitrary C threads. Instead, use the <a class="reference internal" href="#gilstate"><span class="std std-ref">PyGILState API</span></a>.</p> </div> <div class="versionadded"> <p><span class="versionmodified">New in version 2.7.</span></p> </div> </dd></dl> </div> <div class="section" id="profiling-and-tracing"> <span id="profiling"></span><h2>Profiling and Tracing<a class="headerlink" href="#profiling-and-tracing" title="Permalink to this headline">¶</a></h2> <p>The Python interpreter provides some low-level support for attaching profiling and execution tracing facilities. These are used for profiling, debugging, and coverage analysis tools.</p> <p>Starting with Python 2.2, the implementation of this facility was substantially revised, and an interface from C was added. This C interface allows the profiling or tracing code to avoid the overhead of calling through Python-level callable objects, making a direct C function call instead. The essential attributes of the facility have not changed; the interface allows trace functions to be installed per-thread, and the basic events reported to the trace function are the same as had been reported to the Python-level trace functions in previous versions.</p> <dl class="type"> <dt id="c.Py_tracefunc"> int <code class="descname">(*Py_tracefunc)</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em>, PyFrameObject<em> *frame</em>, int<em> what</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *arg</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_tracefunc" title="Permalink to this definition">¶</a></dt> <dd><p>The type of the trace function registered using <a class="reference internal" href="#c.PyEval_SetProfile" title="PyEval_SetProfile"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SetProfile()</span></code></a> and <a class="reference internal" href="#c.PyEval_SetTrace" title="PyEval_SetTrace"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SetTrace()</span></code></a>. The first parameter is the object passed to the registration function as <em>obj</em>, <em>frame</em> is the frame object to which the event pertains, <em>what</em> is one of the constants <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_CALL</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_EXCEPTION</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_LINE</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_RETURN</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_CALL</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_EXCEPTION</span></code>, or <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_RETURN</span></code>, and <em>arg</em> depends on the value of <em>what</em>:</p> <table border="1" class="docutils"> <colgroup> <col width="44%" /> <col width="56%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Value of <em>what</em></th> <th class="head">Meaning of <em>arg</em></th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_CALL</span></code></td> <td>Always <a class="reference internal" href="none.html#c.Py_None" title="Py_None"><code class="xref c c-data docutils literal notranslate"><span class="pre">Py_None</span></code></a>.</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_EXCEPTION</span></code></td> <td>Exception information as returned by <a class="reference internal" href="../library/sys.html#sys.exc_info" title="sys.exc_info"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exc_info()</span></code></a>.</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_LINE</span></code></td> <td>Always <a class="reference internal" href="none.html#c.Py_None" title="Py_None"><code class="xref c c-data docutils literal notranslate"><span class="pre">Py_None</span></code></a>.</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_RETURN</span></code></td> <td>Value being returned to the caller, or <em>NULL</em> if caused by an exception.</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_CALL</span></code></td> <td>Function object being called.</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_EXCEPTION</span></code></td> <td>Function object being called.</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_RETURN</span></code></td> <td>Function object being called.</td> </tr> </tbody> </table> </dd></dl> <dl class="var"> <dt id="c.PyTrace_CALL"> int <code class="descname">PyTrace_CALL</code><a class="headerlink" href="#c.PyTrace_CALL" title="Permalink to this definition">¶</a></dt> <dd><p>The value of the <em>what</em> parameter to a <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tracefunc</span></code></a> function when a new call to a function or method is being reported, or a new entry into a generator. Note that the creation of the iterator for a generator function is not reported as there is no control transfer to the Python bytecode in the corresponding frame.</p> </dd></dl> <dl class="var"> <dt id="c.PyTrace_EXCEPTION"> int <code class="descname">PyTrace_EXCEPTION</code><a class="headerlink" href="#c.PyTrace_EXCEPTION" title="Permalink to this definition">¶</a></dt> <dd><p>The value of the <em>what</em> parameter to a <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tracefunc</span></code></a> function when an exception has been raised. The callback function is called with this value for <em>what</em> when after any bytecode is processed after which the exception becomes set within the frame being executed. The effect of this is that as exception propagation causes the Python stack to unwind, the callback is called upon return to each frame as the exception propagates. Only trace functions receives these events; they are not needed by the profiler.</p> </dd></dl> <dl class="var"> <dt id="c.PyTrace_LINE"> int <code class="descname">PyTrace_LINE</code><a class="headerlink" href="#c.PyTrace_LINE" title="Permalink to this definition">¶</a></dt> <dd><p>The value passed as the <em>what</em> parameter to a trace function (but not a profiling function) when a line-number event is being reported.</p> </dd></dl> <dl class="var"> <dt id="c.PyTrace_RETURN"> int <code class="descname">PyTrace_RETURN</code><a class="headerlink" href="#c.PyTrace_RETURN" title="Permalink to this definition">¶</a></dt> <dd><p>The value for the <em>what</em> parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tracefunc</span></code></a> functions when a call is about to return.</p> </dd></dl> <dl class="var"> <dt id="c.PyTrace_C_CALL"> int <code class="descname">PyTrace_C_CALL</code><a class="headerlink" href="#c.PyTrace_C_CALL" title="Permalink to this definition">¶</a></dt> <dd><p>The value for the <em>what</em> parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tracefunc</span></code></a> functions when a C function is about to be called.</p> </dd></dl> <dl class="var"> <dt id="c.PyTrace_C_EXCEPTION"> int <code class="descname">PyTrace_C_EXCEPTION</code><a class="headerlink" href="#c.PyTrace_C_EXCEPTION" title="Permalink to this definition">¶</a></dt> <dd><p>The value for the <em>what</em> parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tracefunc</span></code></a> functions when a C function has raised an exception.</p> </dd></dl> <dl class="var"> <dt id="c.PyTrace_C_RETURN"> int <code class="descname">PyTrace_C_RETURN</code><a class="headerlink" href="#c.PyTrace_C_RETURN" title="Permalink to this definition">¶</a></dt> <dd><p>The value for the <em>what</em> parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_tracefunc</span></code></a> functions when a C function has returned.</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_SetProfile"> void <code class="descname">PyEval_SetProfile</code><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc">Py_tracefunc</a><em> func</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_SetProfile" title="Permalink to this definition">¶</a></dt> <dd><p>Set the profiler function to <em>func</em>. The <em>obj</em> parameter is passed to the function as its first parameter, and may be any Python object, or <em>NULL</em>. If the profile function needs to maintain state, using a different value for <em>obj</em> for each thread provides a convenient and thread-safe place to store it. The profile function is called for all monitored events except <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_LINE</span></code> and <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_EXCEPTION</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_SetTrace"> void <code class="descname">PyEval_SetTrace</code><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc">Py_tracefunc</a><em> func</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_SetTrace" title="Permalink to this definition">¶</a></dt> <dd><p>Set the tracing function to <em>func</em>. This is similar to <a class="reference internal" href="#c.PyEval_SetProfile" title="PyEval_SetProfile"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SetProfile()</span></code></a>, except the tracing function does receive line-number events and does not receive any event related to C function objects being called. Any trace function registered using <a class="reference internal" href="#c.PyEval_SetTrace" title="PyEval_SetTrace"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyEval_SetTrace()</span></code></a> will not receive <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_CALL</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_EXCEPTION</span></code> or <code class="xref py py-const docutils literal notranslate"><span class="pre">PyTrace_C_RETURN</span></code> as a value for the <em>what</em> parameter.</p> </dd></dl> <dl class="function"> <dt id="c.PyEval_GetCallStats"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyEval_GetCallStats</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *self</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyEval_GetCallStats" title="Permalink to this definition">¶</a></dt> <dd><p>Return a tuple of function call counts. There are constants defined for the positions within the tuple:</p> <table border="1" class="docutils"> <colgroup> <col width="82%" /> <col width="18%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Name</th> <th class="head">Value</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_ALL</span></code></td> <td>0</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_FUNCTION</span></code></td> <td>1</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_FAST_FUNCTION</span></code></td> <td>2</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_FASTER_FUNCTION</span></code></td> <td>3</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_METHOD</span></code></td> <td>4</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_BOUND_METHOD</span></code></td> <td>5</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_CFUNCTION</span></code></td> <td>6</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_TYPE</span></code></td> <td>7</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_GENERATOR</span></code></td> <td>8</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_OTHER</span></code></td> <td>9</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_POP</span></code></td> <td>10</td> </tr> </tbody> </table> <p><code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_FAST_FUNCTION</span></code> means no argument tuple needs to be created. <code class="xref py py-const docutils literal notranslate"><span class="pre">PCALL_FASTER_FUNCTION</span></code> means that the fast-path frame setup code is used.</p> <p>If there is a method call where the call can be optimized by changing the argument tuple and calling the function directly, it gets recorded twice.</p> <p>This function is only present if Python is compiled with <code class="xref py py-const docutils literal notranslate"><span class="pre">CALL_PROFILE</span></code> defined.</p> </dd></dl> </div> <div class="section" id="advanced-debugger-support"> <span id="advanced-debugging"></span><h2>Advanced Debugger Support<a class="headerlink" href="#advanced-debugger-support" title="Permalink to this headline">¶</a></h2> <p>These functions are only intended to be used by advanced debugging tools.</p> <dl class="function"> <dt id="c.PyInterpreterState_Head"> <a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a>* <code class="descname">PyInterpreterState_Head</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyInterpreterState_Head" title="Permalink to this definition">¶</a></dt> <dd><p>Return the interpreter state object at the head of the list of all such objects.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyInterpreterState_Next"> <a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a>* <code class="descname">PyInterpreterState_Next</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a><em> *interp</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyInterpreterState_Next" title="Permalink to this definition">¶</a></dt> <dd><p>Return the next interpreter state object after <em>interp</em> from the list of all such objects.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyInterpreterState_ThreadHead"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> * <code class="descname">PyInterpreterState_ThreadHead</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a><em> *interp</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyInterpreterState_ThreadHead" title="Permalink to this definition">¶</a></dt> <dd><p>Return the pointer to the first <a class="reference internal" href="#c.PyThreadState" title="PyThreadState"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyThreadState</span></code></a> object in the list of threads associated with the interpreter <em>interp</em>.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyThreadState_Next"> <a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a>* <code class="descname">PyThreadState_Next</code><span class="sig-paren">(</span><a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a><em> *tstate</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyThreadState_Next" title="Permalink to this definition">¶</a></dt> <dd><p>Return the next thread state object after <em>tstate</em> from the list of all such objects belonging to the same <a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyInterpreterState</span></code></a> object.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </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="#">Initialization, Finalization, and Threads</a><ul> <li><a class="reference internal" href="#initializing-and-finalizing-the-interpreter">Initializing and finalizing the interpreter</a></li> <li><a class="reference internal" href="#process-wide-parameters">Process-wide parameters</a></li> <li><a class="reference internal" href="#thread-state-and-the-global-interpreter-lock">Thread State and the Global Interpreter Lock</a><ul> <li><a class="reference internal" href="#releasing-the-gil-from-extension-code">Releasing the GIL from extension code</a></li> <li><a class="reference internal" href="#non-python-created-threads">Non-Python created threads</a></li> <li><a class="reference internal" href="#high-level-api">High-level API</a></li> <li><a class="reference internal" href="#low-level-api">Low-level API</a></li> </ul> </li> <li><a class="reference internal" href="#sub-interpreter-support">Sub-interpreter support</a><ul> <li><a class="reference internal" href="#bugs-and-caveats">Bugs and caveats</a></li> </ul> </li> <li><a class="reference internal" href="#asynchronous-notifications">Asynchronous Notifications</a></li> <li><a class="reference internal" href="#profiling-and-tracing">Profiling and Tracing</a></li> <li><a class="reference internal" href="#advanced-debugger-support">Advanced Debugger Support</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="code.html" title="previous chapter">Code Objects</a></p> <h4>Next topic</h4> <p class="topless"><a href="memory.html" title="next chapter">Memory 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