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 <section id="initialization-finalization-and-threads">
<h1>Initialization, Finalization, and Threads<a class="headerlink" href="#initialization-finalization-and-threads" title="Permalink to this headline">¶</a></h1>
<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="c function">
<dt class="sig sig-object c" id="c.Py_Initialize">
void Py_Initialize()<a class="headerlink" href="#c.Py_Initialize" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_SetProgramName()</code></a>, <a class="reference internal" href="#c.Py_SetPythonHome" title="Py_SetPythonHome"><code class="xref c c-func docutils literal notranslate">Py_SetPythonHome()</code></a>, <a class="reference internal" href="#c.PyEval_InitThreads" title="PyEval_InitThreads"><code class="xref c c-func docutils literal notranslate">PyEval_InitThreads()</code></a>,
<a class="reference internal" href="#c.PyEval_ReleaseLock" title="PyEval_ReleaseLock"><code class="xref c c-func docutils literal notranslate">PyEval_ReleaseLock()</code></a>, and <a class="reference internal" href="#c.PyEval_AcquireLock" title="PyEval_AcquireLock"><code class="xref c c-func docutils literal notranslate">PyEval_AcquireLock()</code></a>. This initializes
the table of loaded modules (<code class="docutils literal notranslate">sys.modules</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">__builtin__</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">__main__</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">sys</code></a>. It also initializes
the module search path (<code class="docutils literal notranslate">sys.path</code>). It does not set <code class="docutils literal notranslate">sys.argv</code>; use
<a class="reference internal" href="#c.PySys_SetArgvEx" title="PySys_SetArgvEx"><code class="xref c c-func docutils literal notranslate">PySys_SetArgvEx()</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">Py_Finalize()</code></a> first). There is no return value; it is a
fatal error if the initialization fails.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_InitializeEx">
void Py_InitializeEx(int initsigs)<a class="headerlink" href="#c.Py_InitializeEx" title="Permalink to this definition">¶</a> </dt>
<dd>This function works like <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate">Py_Initialize()</code></a> if initsigs is <code class="docutils literal notranslate">1</code>. If
initsigs is <code class="docutils literal notranslate">0</code>, it skips initialization registration of signal handlers, which
might be useful when Python is embedded.
<div class="versionadded">
New in version 2.4.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_IsInitialized">
int Py_IsInitialized()<a class="headerlink" href="#c.Py_IsInitialized" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_Finalize()</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">Py_Initialize()</code></a> is called again.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_Finalize">
void Py_Finalize()<a class="headerlink" href="#c.Py_Finalize" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_Initialize()</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">Py_NewInterpreter()</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">Py_Initialize()</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">Py_Initialize()</code></a> again first). There is no return
value; errors during finalization are ignored.
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.
Bugs and caveats: The destruction of modules and objects in modules is done
in random order; this may cause destructors (<code class="xref py py-meth docutils literal notranslate">__del__()</code> 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">Py_Initialize()</code></a> and
<a class="reference internal" href="#c.Py_Finalize" title="Py_Finalize"><code class="xref c c-func docutils literal notranslate">Py_Finalize()</code></a> more than once.
</dd></dl>

</section>
<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="c function">
<dt class="sig sig-object c" id="c.Py_SetProgramName">
void Py_SetProgramName(char *name)<a class="headerlink" href="#c.Py_SetProgramName" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_Initialize()</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">argv[0]</code> argument to the <code class="xref c c-func docutils literal notranslate">main()</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">Py_GetPath()</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">'python'</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.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetProgramName">
char *Py_GetProgramName()<a class="headerlink" href="#c.Py_GetProgramName" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_SetProgramName()</code></a>, or the default.
The returned string points into static storage; the caller should not modify its
value.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetPrefix">
char *Py_GetPrefix()<a class="headerlink" href="#c.Py_GetPrefix" title="Permalink to this definition">¶</a> </dt>
<dd>Return the prefix 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">Py_SetProgramName()</code></a> and some environment variables; for example, if the
program name is <code class="docutils literal notranslate">'/usr/local/bin/python'</code>, the prefix is <code class="docutils literal notranslate">'/usr/local'</code>. The
returned string points into static storage; the caller should not modify its
value. This corresponds to the prefix variable in the top-level
<code class="file docutils literal notranslate">Makefile</code> and the <code class="docutils literal notranslate">--prefix</code> argument to the configure
script at build time. The value is available to Python code as <code class="docutils literal notranslate">sys.prefix</code>.
It is only useful on Unix. See also the next function.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetExecPrefix">
char *Py_GetExecPrefix()<a class="headerlink" href="#c.Py_GetExecPrefix" title="Permalink to this definition">¶</a> </dt>
<dd>Return the exec-prefix for installed platform-dependent 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">Py_SetProgramName()</code></a> and some environment variables; for example, if the
program name is <code class="docutils literal notranslate">'/usr/local/bin/python'</code>, the exec-prefix is
<code class="docutils literal notranslate">'/usr/local'</code>. The returned string points into static storage; the caller
should not modify its value. This corresponds to the exec_prefix
variable in the top-level <code class="file docutils literal notranslate">Makefile</code> and the <code class="docutils literal notranslate">--exec-prefix</code>
argument to the configure script at build time. The value is
available to Python code as <code class="docutils literal notranslate">sys.exec_prefix</code>. It is only useful on Unix.
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">/usr/local/plat</code> subtree while platform independent may
be installed in <code class="file docutils literal notranslate">/usr/local</code>.
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!).
System administrators will know how to configure the mount or
automount programs to share <code class="file docutils literal notranslate">/usr/local</code> between platforms
while having <code class="file docutils literal notranslate">/usr/local/plat</code> be a different filesystem for each
platform.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetProgramFullPath">
char *Py_GetProgramFullPath()<a class="headerlink" href="#c.Py_GetProgramFullPath" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_SetProgramName()</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">sys.executable</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetPath">
char *Py_GetPath()<a class="headerlink" href="#c.Py_GetPath" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_SetProgramName()</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">':'</code>
on Unix and Mac OS X, <code class="docutils literal notranslate">';'</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">sys.path</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.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetVersion">
const char *Py_GetVersion()<a class="headerlink" href="#c.Py_GetVersion" title="Permalink to this definition">¶</a> </dt>
<dd>Return the version of this Python interpreter. This is a string that looks
something like
<div class="highlight-default notranslate"><div class="highlight"><pre>&quot;1.5 (#67, Dec 31 1997, 22:34:28) [GCC 2.7.2.2]&quot;
</pre></div>
</div>
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">sys.version</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetPlatform">
const char *Py_GetPlatform()<a class="headerlink" href="#c.Py_GetPlatform" title="Permalink to this definition">¶</a> </dt>
<dd>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">'sunos5'</code>. On Mac OS X, it is
<code class="docutils literal notranslate">'darwin'</code>. On Windows, it is <code class="docutils literal notranslate">'win'</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">sys.platform</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetCopyright">
const char *Py_GetCopyright()<a class="headerlink" href="#c.Py_GetCopyright" title="Permalink to this definition">¶</a> </dt>
<dd>Return the official copyright string for the current Python version, for example
<code class="docutils literal notranslate">'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'</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">sys.copyright</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetCompiler">
const char *Py_GetCompiler()<a class="headerlink" href="#c.Py_GetCompiler" title="Permalink to this definition">¶</a> </dt>
<dd>Return an indication of the compiler used to build the current Python version,
in square brackets, for example:
<div class="highlight-default notranslate"><div class="highlight"><pre>&quot;[GCC 2.7.2.2]&quot;
</pre></div>
</div>
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">sys.version</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetBuildInfo">
const char *Py_GetBuildInfo()<a class="headerlink" href="#c.Py_GetBuildInfo" title="Permalink to this definition">¶</a> </dt>
<dd>Return information about the sequence number and build date and time of the
current Python interpreter instance, for example
<div class="highlight-default notranslate"><div class="highlight"><pre>&quot;#67, Aug 1 1997, 22:34:28&quot;
</pre></div>
</div>
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">sys.version</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PySys_SetArgvEx">
void PySys_SetArgvEx(int argc, char **argv, int updatepath)<a class="headerlink" href="#c.PySys_SetArgvEx" title="Permalink to this definition">¶</a> </dt>
<dd>Set <a class="reference internal" href="../library/sys.html#sys.argv" title="sys.argv"><code class="xref py py-data docutils literal notranslate">sys.argv</code></a> based on argc and argv. These parameters are
similar to those passed to the program’s <code class="xref c c-func docutils literal notranslate">main()</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 argv 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">sys.argv</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">Py_FatalError()</code></a>.
If updatepath is zero, this is all the function does. If updatepath
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">sys.path</code></a> according to the
following algorithm:
<ul class="simple">
<li>If the name of an existing script is passed in <code class="docutils literal notranslate">argv[0]</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">sys.path</code></a>.</li>
<li>Otherwise (that is, if argc is 0 or <code class="docutils literal notranslate">argv[0]</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">sys.path</code></a>, which is the same as prepending the current working
directory (<code class="docutils literal notranslate">&quot;.&quot;</code>).</li>
</ul>
<div class="admonition note">
Note
It is recommended that applications embedding the Python interpreter
for purposes other than executing a single script pass <code class="docutils literal notranslate">0</code> as updatepath,
and update <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</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>.
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">sys.path</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">PySys_SetArgv()</code></a>, for example using:
<div class="highlight-default notranslate"><div class="highlight"><pre>PyRun_SimpleString(&quot;import sys; sys.path.pop(0)\n&quot;);
</pre></div>
</div>
</div>
<div class="versionadded">
New in version 2.6.6.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PySys_SetArgv">
void PySys_SetArgv(int argc, char **argv)<a class="headerlink" href="#c.PySys_SetArgv" title="Permalink to this definition">¶</a> </dt>
<dd>This function works like <a class="reference internal" href="#c.PySys_SetArgvEx" title="PySys_SetArgvEx"><code class="xref c c-func docutils literal notranslate">PySys_SetArgvEx()</code></a> with updatepath set to <code class="docutils literal notranslate">1</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_SetPythonHome">
void Py_SetPythonHome(char *home)<a class="headerlink" href="#c.Py_SetPythonHome" title="Permalink to this definition">¶</a> </dt>
<dd>Set the default “home” directory, that is, the location of the standard
Python libraries. See <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate">PYTHONHOME</code></a> for the meaning of the
argument string.
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.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GetPythonHome">
char *Py_GetPythonHome()<a class="headerlink" href="#c.Py_GetPythonHome" title="Permalink to this definition">¶</a> </dt>
<dd>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">Py_SetPythonHome()</code></a>, or the value of the <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate">PYTHONHOME</code></a>
environment variable if it is set.
</dd></dl>

</section>
<section id="thread-state-and-the-global-interpreter-lock">
<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>
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">global
interpreter lock</a> or <a class="reference internal" href="../glossary.html#term-GIL">GIL</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.
Therefore, the rule exists that only the thread that has acquired the
<a class="reference internal" href="../glossary.html#term-GIL">GIL</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">sys.setcheckinterval()</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.
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">PyThreadState</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">PyThreadState</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">PyThreadState_Get()</code></a>.
<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>
Most extension code manipulating the <a class="reference internal" href="../glossary.html#term-GIL">GIL</a> has the following simple
structure:
<div class="highlight-default notranslate"><div class="highlight"><pre>Save the thread state in a local variable.
Release the global interpreter lock.
... Do some blocking I/O operation ...
Reacquire the global interpreter lock.
Restore the thread state from the local variable.
</pre></div>
</div>
This is so common that a pair of macros exists to simplify it:
<div class="highlight-default notranslate"><div class="highlight"><pre>Py_BEGIN_ALLOW_THREADS
... Do some blocking I/O operation ...
Py_END_ALLOW_THREADS
</pre></div>
</div>
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">Py_BEGIN_ALLOW_THREADS</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">Py_END_ALLOW_THREADS</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).
When thread support is enabled, the block above expands to the following code:
<div class="highlight-default notranslate"><div class="highlight"><pre>PyThreadState *_save;

_save = PyEval_SaveThread();
...Do some blocking I/O operation...
PyEval_RestoreThread(_save);
</pre></div>
</div>
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.
<div class="admonition note">
Note
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">zlib</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">hashlib</code></a> modules release the GIL when
compressing or hashing data.
</div>
</section>
<section id="non-python-created-threads">
<h3>Non-Python created threads<a class="headerlink" href="#non-python-created-threads" title="Permalink to this headline">¶</a></h3>
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">threading</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.
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.
The <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate">PyGILState_Ensure()</code></a> and <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate">PyGILState_Release()</code></a> functions do
all of the above automatically. The typical idiom for calling into Python
from a C thread is:
<div class="highlight-default notranslate"><div class="highlight"><pre>PyGILState_STATE gstate;
gstate = PyGILState_Ensure();

/* Perform Python actions here. */
result = CallSomeFunction();
/* evaluate result or handle exception */

/* Release the thread. No Python API allowed beyond this point. */
PyGILState_Release(gstate);
</pre></div>
</div>
Note that the <code class="xref c c-func docutils literal notranslate">PyGILState_*()</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">Py_Initialize()</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">Py_NewInterpreter()</code></a>), but mixing multiple interpreters and the
<code class="xref c c-func docutils literal notranslate">PyGILState_*()</code> API is unsupported.
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">fork()</code> call. On most systems with <code class="xref c c-func docutils literal notranslate">fork()</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">os.fork()</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">Lock Objects</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">pthread_atfork()</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">fork()</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">os.fork()</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">PyOS_AfterFork()</code></a> tries to reset the necessary locks, but is not
always able to.
</section>
<section id="high-level-api">
<h3>High-level API<a class="headerlink" href="#high-level-api" title="Permalink to this headline">¶</a></h3>
These are the most commonly used types and functions when writing C extension
code, or when embedding the Python interpreter:
<dl class="c type">
<dt class="sig sig-object c" id="c.PyInterpreterState">
type PyInterpreterState<a class="headerlink" href="#c.PyInterpreterState" title="Permalink to this definition">¶</a> </dt>
<dd>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.
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.
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyThreadState">
type PyThreadState<a class="headerlink" href="#c.PyThreadState" title="Permalink to this definition">¶</a> </dt>
<dd>This data structure represents the state of a single thread. The only public
data member is <code class="xref c c-type docutils literal notranslate">PyInterpreterState *</code><code class="xref py py-attr docutils literal notranslate">interp</code>, which points to
this thread’s interpreter state.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_InitThreads">
void PyEval_InitThreads()<a class="headerlink" href="#c.PyEval_InitThreads" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyEval_ReleaseLock()</code></a> or
<code class="docutils literal notranslate">PyEval_ReleaseThread(tstate)</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">PyEval_SaveThread()</code></a> or <a class="reference internal" href="#c.PyEval_RestoreThread" title="PyEval_RestoreThread"><code class="xref c c-func docutils literal notranslate">PyEval_RestoreThread()</code></a>.
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">Py_Initialize()</code></a>.
<div class="admonition note" id="index-20">
Note
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">_thread</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">PyEval_InitThreads()</code></a>. When this call returns, it is guaranteed that
the lock has been created and that the calling thread has acquired it.
It is not safe to call this function when it is unknown which thread (if
any) currently has the global interpreter lock.
This function is not available when thread support is disabled at compile time.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_ThreadsInitialized">
int PyEval_ThreadsInitialized()<a class="headerlink" href="#c.PyEval_ThreadsInitialized" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyEval_InitThreads()</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.
<div class="versionadded">
New in version 2.4.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_SaveThread">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyEval_SaveThread()<a class="headerlink" href="#c.PyEval_SaveThread" title="Permalink to this definition">¶</a> </dt>
<dd>Release the global interpreter lock (if it has been created and thread
support is enabled) and reset the thread state to NULL, returning the
previous thread state (which is not NULL). 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.)
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_RestoreThread">
void PyEval_RestoreThread(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyEval_RestoreThread" title="Permalink to this definition">¶</a> </dt>
<dd>Acquire the global interpreter lock (if it has been created and thread
support is enabled) and set the thread state to tstate, which must not be
NULL. 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.)
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_Get">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyThreadState_Get()<a class="headerlink" href="#c.PyThreadState_Get" title="Permalink to this definition">¶</a> </dt>
<dd>Return the current thread state. The global interpreter lock must be held.
When the current thread state is NULL, this issues a fatal error (so that
the caller needn’t check for NULL).
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_Swap">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyThreadState_Swap(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyThreadState_Swap" title="Permalink to this definition">¶</a> </dt>
<dd>Swap the current thread state with the thread state given by the argument
tstate, which may be NULL. The global interpreter lock must be held
and is not released.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_ReInitThreads">
void PyEval_ReInitThreads()<a class="headerlink" href="#c.PyEval_ReInitThreads" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyOS_AfterFork()</code></a> to ensure that newly
created child processes don’t hold locks referring to threads which
are not running in the child process.
</dd></dl>

The following functions use thread-local storage, and are not compatible
with sub-interpreters:
<dl class="c function">
<dt class="sig sig-object c" id="c.PyGILState_Ensure">
PyGILState_STATE PyGILState_Ensure()<a class="headerlink" href="#c.PyGILState_Ensure" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyGILState_Release()</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">PyGILState_Ensure()</code></a> and
<a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate">PyGILState_Release()</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">Py_BEGIN_ALLOW_THREADS</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">Py_END_ALLOW_THREADS</code></a> macros is
acceptable.
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">PyGILState_Ensure()</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">PyGILState_Release()</code></a> to ensure Python is left in the same state. Even
though recursive calls are allowed, these handles cannot 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">PyGILState_Ensure()</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">PyGILState_Release()</code></a>.
When the function returns, the current thread will hold the GIL and be able
to call arbitrary Python code. Failure is a fatal error.
<div class="versionadded">
New in version 2.3.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyGILState_Release">
void PyGILState_Release(PyGILState_STATE)<a class="headerlink" href="#c.PyGILState_Release" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyGILState_Ensure()</code></a> call
(but generally this state will be unknown to the caller, hence the use of the
GILState API).
Every call to <a class="reference internal" href="#c.PyGILState_Ensure" title="PyGILState_Ensure"><code class="xref c c-func docutils literal notranslate">PyGILState_Ensure()</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">PyGILState_Release()</code></a> on the same thread.
<div class="versionadded">
New in version 2.3.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyGILState_GetThisThreadState">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyGILState_GetThisThreadState()<a class="headerlink" href="#c.PyGILState_GetThisThreadState" title="Permalink to this definition">¶</a> </dt>
<dd>Get the current thread state for this thread. May return <code class="docutils literal notranslate">NULL</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.
<div class="versionadded">
New in version 2.3.
</div>
</dd></dl>

The following macros are normally used without a trailing semicolon; look for
example usage in the Python source distribution.
<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_BEGIN_ALLOW_THREADS">
Py_BEGIN_ALLOW_THREADS<a class="headerlink" href="#c.Py_BEGIN_ALLOW_THREADS" title="Permalink to this definition">¶</a> </dt>
<dd>This macro expands to <code class="docutils literal notranslate">{ PyThreadState *_save; _save = PyEval_SaveThread();</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">Py_END_ALLOW_THREADS</code></a> macro. See above for further discussion of this
macro. It is a no-op when thread support is disabled at compile time.
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_END_ALLOW_THREADS">
Py_END_ALLOW_THREADS<a class="headerlink" href="#c.Py_END_ALLOW_THREADS" title="Permalink to this definition">¶</a> </dt>
<dd>This macro expands to <code class="docutils literal notranslate">PyEval_RestoreThread(_save); }</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">Py_BEGIN_ALLOW_THREADS</code></a> macro. See above for further discussion of
this macro. It is a no-op when thread support is disabled at compile time.
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_BLOCK_THREADS">
Py_BLOCK_THREADS<a class="headerlink" href="#c.Py_BLOCK_THREADS" title="Permalink to this definition">¶</a> </dt>
<dd>This macro expands to <code class="docutils literal notranslate">PyEval_RestoreThread(_save);</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">Py_END_ALLOW_THREADS</code></a> without the closing brace. It is a no-op when
thread support is disabled at compile time.
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_UNBLOCK_THREADS">
Py_UNBLOCK_THREADS<a class="headerlink" href="#c.Py_UNBLOCK_THREADS" title="Permalink to this definition">¶</a> </dt>
<dd>This macro expands to <code class="docutils literal notranslate">_save = PyEval_SaveThread();</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">Py_BEGIN_ALLOW_THREADS</code></a> without the opening brace and variable
declaration. It is a no-op when thread support is disabled at compile time.
</dd></dl>

</section>
<section id="low-level-api">
<h3>Low-level API<a class="headerlink" href="#low-level-api" title="Permalink to this headline">¶</a></h3>
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.
<dl class="c function">
<dt class="sig sig-object c" id="c.PyInterpreterState_New">
<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *PyInterpreterState_New()<a class="headerlink" href="#c.PyInterpreterState_New" title="Permalink to this definition">¶</a> </dt>
<dd>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.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyInterpreterState_Clear">
void PyInterpreterState_Clear(<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *interp)<a class="headerlink" href="#c.PyInterpreterState_Clear" title="Permalink to this definition">¶</a> </dt>
<dd>Reset all information in an interpreter state object. The global interpreter
lock must be held.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyInterpreterState_Delete">
void PyInterpreterState_Delete(<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *interp)<a class="headerlink" href="#c.PyInterpreterState_Delete" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyInterpreterState_Clear()</code></a>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_New">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyThreadState_New(<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *interp)<a class="headerlink" href="#c.PyThreadState_New" title="Permalink to this definition">¶</a> </dt>
<dd>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.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_Clear">
void PyThreadState_Clear(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyThreadState_Clear" title="Permalink to this definition">¶</a> </dt>
<dd>Reset all information in a thread state object. The global interpreter lock
must be held.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_Delete">
void PyThreadState_Delete(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyThreadState_Delete" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyThreadState_Clear()</code></a>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_GetDict">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *PyThreadState_GetDict()<a class="headerlink" href="#c.PyThreadState_GetDict" title="Permalink to this definition">¶</a> </dt>
<dd>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 NULL, no exception has been raised and
the caller should assume no current thread state is available.
<div class="versionchanged">
Changed in version 2.3: Previously this could only be called when a current thread is active, and NULL
meant that an exception was raised.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_SetAsyncExc">
int PyThreadState_SetAsyncExc(long id, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *exc)<a class="headerlink" href="#c.PyThreadState_SetAsyncExc" title="Permalink to this definition">¶</a> </dt>
<dd>Asynchronously raise an exception in a thread. The id argument is the thread
id of the target thread; exc is the exception object to be raised. This
function does not steal any references to exc. 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 exc is <code class="xref py py-const docutils literal notranslate">NULL</code>, the pending
exception (if any) for the thread is cleared. This raises no exceptions.
<div class="versionadded">
New in version 2.3.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_AcquireThread">
void PyEval_AcquireThread(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyEval_AcquireThread" title="Permalink to this definition">¶</a> </dt>
<dd>Acquire the global interpreter lock and set the current thread state to
tstate, which should not be NULL. The lock must have been created earlier.
If this thread already has the lock, deadlock ensues.
<a class="reference internal" href="#c.PyEval_RestoreThread" title="PyEval_RestoreThread"><code class="xref c c-func docutils literal notranslate">PyEval_RestoreThread()</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).
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_ReleaseThread">
void PyEval_ReleaseThread(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyEval_ReleaseThread" title="Permalink to this definition">¶</a> </dt>
<dd>Reset the current thread state to NULL and release the global interpreter
lock. The lock must have been created earlier and must be held by the current
thread. The tstate argument, which must not be NULL, is only used to check
that it represents the current thread state — if it isn’t, a fatal error is
reported.
<a class="reference internal" href="#c.PyEval_SaveThread" title="PyEval_SaveThread"><code class="xref c c-func docutils literal notranslate">PyEval_SaveThread()</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).
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_AcquireLock">
void PyEval_AcquireLock()<a class="headerlink" href="#c.PyEval_AcquireLock" title="Permalink to this definition">¶</a> </dt>
<dd>Acquire the global interpreter lock. The lock must have been created earlier.
If this thread already has the lock, a deadlock ensues.
<div class="admonition warning">
Warning
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">PyEval_RestoreThread()</code></a> or <a class="reference internal" href="#c.PyEval_AcquireThread" title="PyEval_AcquireThread"><code class="xref c c-func docutils literal notranslate">PyEval_AcquireThread()</code></a>
instead.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_ReleaseLock">
void PyEval_ReleaseLock()<a class="headerlink" href="#c.PyEval_ReleaseLock" title="Permalink to this definition">¶</a> </dt>
<dd>Release the global interpreter lock. The lock must have been created earlier.
<div class="admonition warning">
Warning
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">PyEval_SaveThread()</code></a> or <a class="reference internal" href="#c.PyEval_ReleaseThread" title="PyEval_ReleaseThread"><code class="xref c c-func docutils literal notranslate">PyEval_ReleaseThread()</code></a>
instead.
</div>
</dd></dl>

</section>
</section>
<section id="sub-interpreter-support">
<h2>Sub-interpreter support<a class="headerlink" href="#sub-interpreter-support" title="Permalink to this headline">¶</a></h2>
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">PyThreadState_Swap()</code></a> function. You can create and destroy them
using the following functions:
<dl class="c function">
<dt class="sig sig-object c" id="c.Py_NewInterpreter">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *Py_NewInterpreter()<a class="headerlink" href="#c.Py_NewInterpreter" title="Permalink to this definition">¶</a> </dt>
<dd>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">builtins</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">__main__</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">sys</code></a>. The
table of loaded modules (<code class="docutils literal notranslate">sys.modules</code>) and the module search path
(<code class="docutils literal notranslate">sys.path</code>) are also separate. The new environment has no <code class="docutils literal notranslate">sys.argv</code>
variable. It has new standard I/O stream file objects <code class="docutils literal notranslate">sys.stdin</code>,
<code class="docutils literal notranslate">sys.stdout</code> and <code class="docutils literal notranslate">sys.stderr</code> (however these refer to the same underlying
file descriptors).
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, NULL 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.)
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">init</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">Py_Finalize()</code></a> and <a class="reference internal" href="#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate">Py_Initialize()</code></a>; in that case, the extension’s
<code class="docutils literal notranslate">initmodule</code> function is called again.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_EndInterpreter">
void Py_EndInterpreter(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.Py_EndInterpreter" title="Permalink to this definition">¶</a> </dt>
<dd>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 NULL. 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">Py_Finalize()</code></a> will destroy all sub-interpreters that
haven’t been explicitly destroyed at that point.
</dd></dl>

<section id="bugs-and-caveats">
<h3>Bugs and caveats<a class="headerlink" href="#bugs-and-caveats" title="Permalink to this headline">¶</a></h3>
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">os.close()</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.
Also note that combining this functionality with <code class="xref c c-func docutils literal notranslate">PyGILState_*()</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">PyGILState_Ensure()</code></a> and <a class="reference internal" href="#c.PyGILState_Release" title="PyGILState_Release"><code class="xref c c-func docutils literal notranslate">PyGILState_Release()</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">ctypes</code></a>) using these APIs to allow calling
of Python code from non-Python created threads will probably be broken when using
sub-interpreters.
</section>
</section>
<section id="asynchronous-notifications">
<h2>Asynchronous Notifications<a class="headerlink" href="#asynchronous-notifications" title="Permalink to this headline">¶</a></h2>
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.
<dl class="c function">
<dt class="sig sig-object c" id="c.Py_AddPendingCall">
int Py_AddPendingCall(int (*func)(void*), void *arg)<a class="headerlink" href="#c.Py_AddPendingCall" title="Permalink to this definition">¶</a> </dt>
<dd>Schedule a function to be called from the main interpreter thread. On
success, <code class="docutils literal notranslate">0</code> is returned and func is queued for being called in the
main thread. On failure, <code class="docutils literal notranslate">-1</code> is returned without setting any exception.
When successfully queued, func will be eventually called from the
main interpreter thread with the argument arg. It will be called
asynchronously with respect to normally running Python code, but with
both these conditions met:
<ul class="simple">
<li>on a <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> boundary;</li>
<li>with the main thread holding the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock">global interpreter lock</a>
(func can therefore use the full C API).</li>
</ul>
func must return <code class="docutils literal notranslate">0</code> on success, or <code class="docutils literal notranslate">-1</code> on failure with an exception
set. func 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.
This function doesn’t need a current thread state to run, and it doesn’t
need the global interpreter lock.
<div class="admonition warning">
Warning
This is a low-level function, only useful for very special cases.
There is no guarantee that func will be called as quick as
possible. If the main thread is busy executing a system call,
func won’t be called before the system call returns. This
function is generally not suitable for calling Python code from
arbitrary C threads. Instead, use the <a class="reference internal" href="#gilstate">PyGILState API</a>.
</div>
<div class="versionadded">
New in version 2.7.
</div>
</dd></dl>

</section>
<section id="profiling-and-tracing">
<h2>Profiling and Tracing<a class="headerlink" href="#profiling-and-tracing" title="Permalink to this headline">¶</a></h2>
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.
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.
<dl class="c type">
<dt class="sig sig-object c" id="c.Py_tracefunc">
typedef int (*Py_tracefunc)(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *obj, PyFrameObject *frame, int what, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *arg)<a class="headerlink" href="#c.Py_tracefunc" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyEval_SetProfile()</code></a> and
<a class="reference internal" href="#c.PyEval_SetTrace" title="PyEval_SetTrace"><code class="xref c c-func docutils literal notranslate">PyEval_SetTrace()</code></a>. The first parameter is the object passed to the
registration function as obj, frame is the frame object to which the event
pertains, what is one of the constants <code class="xref py py-const docutils literal notranslate">PyTrace_CALL</code>,
<code class="xref py py-const docutils literal notranslate">PyTrace_EXCEPTION</code>, <code class="xref py py-const docutils literal notranslate">PyTrace_LINE</code>, <code class="xref py py-const docutils literal notranslate">PyTrace_RETURN</code>,
<code class="xref py py-const docutils literal notranslate">PyTrace_C_CALL</code>, <code class="xref py py-const docutils literal notranslate">PyTrace_C_EXCEPTION</code>, or
<code class="xref py py-const docutils literal notranslate">PyTrace_C_RETURN</code>, and arg depends on the value of what:
<table class="docutils align-default">
<colgroup>
<col style="width: 44%" />
<col style="width: 56%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Value of what</th>
<th class="head">Meaning of arg</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PyTrace_CALL</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">Py_None</code></a>.</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PyTrace_EXCEPTION</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">sys.exc_info()</code></a>.</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PyTrace_LINE</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">Py_None</code></a>.</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PyTrace_RETURN</code></td>
<td>Value being returned to the caller,
or NULL if caused by an exception.</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PyTrace_C_CALL</code></td>
<td>Function object being called.</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PyTrace_C_EXCEPTION</code></td>
<td>Function object being called.</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PyTrace_C_RETURN</code></td>
<td>Function object being called.</td>
</tr>
</tbody>
</table>
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_CALL">
int PyTrace_CALL<a class="headerlink" href="#c.PyTrace_CALL" title="Permalink to this definition">¶</a> </dt>
<dd>The value of the what parameter to a <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate">Py_tracefunc</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.
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_EXCEPTION">
int PyTrace_EXCEPTION<a class="headerlink" href="#c.PyTrace_EXCEPTION" title="Permalink to this definition">¶</a> </dt>
<dd>The value of the what parameter to a <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate">Py_tracefunc</code></a> function when an
exception has been raised. The callback function is called with this value for
what 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.
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_LINE">
int PyTrace_LINE<a class="headerlink" href="#c.PyTrace_LINE" title="Permalink to this definition">¶</a> </dt>
<dd>The value passed as the what parameter to a trace function (but not a
profiling function) when a line-number event is being reported.
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_RETURN">
int PyTrace_RETURN<a class="headerlink" href="#c.PyTrace_RETURN" title="Permalink to this definition">¶</a> </dt>
<dd>The value for the what parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate">Py_tracefunc</code></a> functions when a
call is about to return.
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_C_CALL">
int PyTrace_C_CALL<a class="headerlink" href="#c.PyTrace_C_CALL" title="Permalink to this definition">¶</a> </dt>
<dd>The value for the what parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate">Py_tracefunc</code></a> functions when a C
function is about to be called.
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_C_EXCEPTION">
int PyTrace_C_EXCEPTION<a class="headerlink" href="#c.PyTrace_C_EXCEPTION" title="Permalink to this definition">¶</a> </dt>
<dd>The value for the what parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate">Py_tracefunc</code></a> functions when a C
function has raised an exception.
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyTrace_C_RETURN">
int PyTrace_C_RETURN<a class="headerlink" href="#c.PyTrace_C_RETURN" title="Permalink to this definition">¶</a> </dt>
<dd>The value for the what parameter to <a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc"><code class="xref c c-type docutils literal notranslate">Py_tracefunc</code></a> functions when a C
function has returned.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_SetProfile">
void PyEval_SetProfile(<a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc">Py_tracefunc</a> func, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *obj)<a class="headerlink" href="#c.PyEval_SetProfile" title="Permalink to this definition">¶</a> </dt>
<dd>Set the profiler function to func. The obj parameter is passed to the
function as its first parameter, and may be any Python object, or NULL. If
the profile function needs to maintain state, using a different value for obj
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">PyTrace_LINE</code>
and <code class="xref py py-const docutils literal notranslate">PyTrace_EXCEPTION</code>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_SetTrace">
void PyEval_SetTrace(<a class="reference internal" href="#c.Py_tracefunc" title="Py_tracefunc">Py_tracefunc</a> func, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *obj)<a class="headerlink" href="#c.PyEval_SetTrace" title="Permalink to this definition">¶</a> </dt>
<dd>Set the tracing function to func. This is similar to
<a class="reference internal" href="#c.PyEval_SetProfile" title="PyEval_SetProfile"><code class="xref c c-func docutils literal notranslate">PyEval_SetProfile()</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">PyEval_SetTrace()</code></a> will not receive
<code class="xref py py-const docutils literal notranslate">PyTrace_C_CALL</code>, <code class="xref py py-const docutils literal notranslate">PyTrace_C_EXCEPTION</code> or <code class="xref py py-const docutils literal notranslate">PyTrace_C_RETURN</code>
as a value for the what parameter.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyEval_GetCallStats">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *PyEval_GetCallStats(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *self)<a class="headerlink" href="#c.PyEval_GetCallStats" title="Permalink to this definition">¶</a> </dt>
<dd>Return a tuple of function call counts. There are constants defined for the
positions within the tuple:
<table class="docutils align-default">
<colgroup>
<col style="width: 82%" />
<col style="width: 18%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Name</th>
<th class="head">Value</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PCALL_ALL</code></td>
<td>0</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PCALL_FUNCTION</code></td>
<td>1</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PCALL_FAST_FUNCTION</code></td>
<td>2</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PCALL_FASTER_FUNCTION</code></td>
<td>3</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PCALL_METHOD</code></td>
<td>4</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PCALL_BOUND_METHOD</code></td>
<td>5</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PCALL_CFUNCTION</code></td>
<td>6</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PCALL_TYPE</code></td>
<td>7</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PCALL_GENERATOR</code></td>
<td>8</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate">PCALL_OTHER</code></td>
<td>9</td>
</tr>
<tr class="row-even"><td><code class="xref py py-const docutils literal notranslate">PCALL_POP</code></td>
<td>10</td>
</tr>
</tbody>
</table>
<code class="xref py py-const docutils literal notranslate">PCALL_FAST_FUNCTION</code> means no argument tuple needs to be created.
<code class="xref py py-const docutils literal notranslate">PCALL_FASTER_FUNCTION</code> means that the fast-path frame setup code is used.
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.
This function is only present if Python is compiled with <code class="xref py py-const docutils literal notranslate">CALL_PROFILE</code>
defined.
</dd></dl>

</section>
<section id="advanced-debugger-support">
<h2>Advanced Debugger Support<a class="headerlink" href="#advanced-debugger-support" title="Permalink to this headline">¶</a></h2>
These functions are only intended to be used by advanced debugging tools.
<dl class="c function">
<dt class="sig sig-object c" id="c.PyInterpreterState_Head">
<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *PyInterpreterState_Head()<a class="headerlink" href="#c.PyInterpreterState_Head" title="Permalink to this definition">¶</a> </dt>
<dd>Return the interpreter state object at the head of the list of all such objects.
<div class="versionadded">
New in version 2.2.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyInterpreterState_Next">
<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *PyInterpreterState_Next(<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *interp)<a class="headerlink" href="#c.PyInterpreterState_Next" title="Permalink to this definition">¶</a> </dt>
<dd>Return the next interpreter state object after interp from the list of all
such objects.
<div class="versionadded">
New in version 2.2.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyInterpreterState_ThreadHead">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyInterpreterState_ThreadHead(<a class="reference internal" href="#c.PyInterpreterState" title="PyInterpreterState">PyInterpreterState</a> *interp)<a class="headerlink" href="#c.PyInterpreterState_ThreadHead" title="Permalink to this definition">¶</a> </dt>
<dd>Return the pointer to the first <a class="reference internal" href="#c.PyThreadState" title="PyThreadState"><code class="xref c c-type docutils literal notranslate">PyThreadState</code></a> object in the list of
threads associated with the interpreter interp.
<div class="versionadded">
New in version 2.2.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyThreadState_Next">
<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *PyThreadState_Next(<a class="reference internal" href="#c.PyThreadState" title="PyThreadState">PyThreadState</a> *tstate)<a class="headerlink" href="#c.PyThreadState_Next" title="Permalink to this definition">¶</a> </dt>
<dd>Return the next thread state object after tstate 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">PyInterpreterState</code></a> object.
<div class="versionadded">
New in version 2.2.
</div>
</dd></dl>

</section>
</section>

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 <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>
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<li><a class="reference internal" href="#bugs-and-caveats">Bugs and caveats</a></li>
</ul>
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<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>

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