--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Doc/c-api/init.rst Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,982 @@
+.. highlightlang:: c
+
+
+.. _initialization:
+
+*****************************************
+Initialization, Finalization, and Threads
+*****************************************
+
+
+.. cfunction:: void Py_Initialize()
+
+ .. index::
+ single: Py_SetProgramName()
+ single: PyEval_InitThreads()
+ single: PyEval_ReleaseLock()
+ single: PyEval_AcquireLock()
+ single: modules (in module sys)
+ single: path (in module sys)
+ module: __builtin__
+ module: __main__
+ module: sys
+ triple: module; search; path
+ single: PySys_SetArgv()
+ single: Py_Finalize()
+
+ 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 :cfunc:`Py_SetProgramName`, :cfunc:`PyEval_InitThreads`,
+ :cfunc:`PyEval_ReleaseLock`, and :cfunc:`PyEval_AcquireLock`. This initializes
+ the table of loaded modules (``sys.modules``), and creates the fundamental
+ modules :mod:`__builtin__`, :mod:`__main__` and :mod:`sys`. It also initializes
+ the module search path (``sys.path``). It does not set ``sys.argv``; use
+ :cfunc:`PySys_SetArgv` for that. This is a no-op when called for a second time
+ (without calling :cfunc:`Py_Finalize` first). There is no return value; it is a
+ fatal error if the initialization fails.
+
+
+.. cfunction:: void Py_InitializeEx(int initsigs)
+
+ This function works like :cfunc:`Py_Initialize` if *initsigs* is 1. If
+ *initsigs* is 0, it skips initialization registration of signal handlers, which
+ might be useful when Python is embedded.
+
+ .. versionadded:: 2.4
+
+
+.. cfunction:: int Py_IsInitialized()
+
+ Return true (nonzero) when the Python interpreter has been initialized, false
+ (zero) if not. After :cfunc:`Py_Finalize` is called, this returns false until
+ :cfunc:`Py_Initialize` is called again.
+
+
+.. cfunction:: void Py_Finalize()
+
+ Undo all initializations made by :cfunc:`Py_Initialize` and subsequent use of
+ Python/C API functions, and destroy all sub-interpreters (see
+ :cfunc:`Py_NewInterpreter` below) that were created and not yet destroyed since
+ the last call to :cfunc:`Py_Initialize`. Ideally, this frees all memory
+ allocated by the Python interpreter. This is a no-op when called for a second
+ time (without calling :cfunc:`Py_Initialize` 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 (:meth:`__del__` 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 :cfunc:`Py_Initialize` and
+ :cfunc:`Py_Finalize` more than once.
+
+
+.. cfunction:: PyThreadState* Py_NewInterpreter()
+
+ .. index::
+ module: __builtin__
+ module: __main__
+ module: sys
+ single: stdout (in module sys)
+ single: stderr (in module sys)
+ single: stdin (in module sys)
+
+ 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 :mod:`__builtin__`, :mod:`__main__` and :mod:`sys`. The
+ table of loaded modules (``sys.modules``) and the module search path
+ (``sys.path``) are also separate. The new environment has no ``sys.argv``
+ variable. It has new standard I/O stream file objects ``sys.stdin``,
+ ``sys.stdout`` and ``sys.stderr`` (however these refer to the same underlying
+ :ctype:`FILE` structures in the C library).
+
+ 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.)
+
+ .. index::
+ single: Py_Finalize()
+ single: Py_Initialize()
+
+ 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 ``init`` 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
+ :cfunc:`Py_Finalize` and :cfunc:`Py_Initialize`; in that case, the extension's
+ ``initmodule`` function *is* called again.
+
+ .. index:: single: close() (in module os)
+
+ **Bugs and caveats:** 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 :func:`os.close` 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. (XXX This is a hard-to-fix bug that will be addressed in a future
+ release.)
+
+ Also note that the use of this functionality is incompatible with extension
+ modules such as PyObjC and ctypes that use the :cfunc:`PyGILState_\*` APIs (and
+ this is inherent in the way the :cfunc:`PyGILState_\*` functions work). Simple
+ things may work, but confusing behavior will always be near.
+
+
+.. cfunction:: void Py_EndInterpreter(PyThreadState *tstate)
+
+ .. index:: single: Py_Finalize()
+
+ 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.) :cfunc:`Py_Finalize` will destroy all sub-interpreters that
+ haven't been explicitly destroyed at that point.
+
+
+.. cfunction:: void Py_SetProgramName(char *name)
+
+ .. index::
+ single: Py_Initialize()
+ single: main()
+ single: Py_GetPath()
+
+ This function should be called before :cfunc:`Py_Initialize` is called for
+ the first time, if it is called at all. It tells the interpreter the value
+ of the ``argv[0]`` argument to the :cfunc:`main` function of the program.
+ This is used by :cfunc:`Py_GetPath` and some other functions below to find
+ the Python run-time libraries relative to the interpreter executable. The
+ default value is ``'python'``. 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.
+
+
+.. cfunction:: char* Py_GetProgramName()
+
+ .. index:: single: Py_SetProgramName()
+
+ Return the program name set with :cfunc:`Py_SetProgramName`, or the default.
+ The returned string points into static storage; the caller should not modify its
+ value.
+
+
+.. cfunction:: char* Py_GetPrefix()
+
+ Return the *prefix* for installed platform-independent files. This is derived
+ through a number of complicated rules from the program name set with
+ :cfunc:`Py_SetProgramName` and some environment variables; for example, if the
+ program name is ``'/usr/local/bin/python'``, the prefix is ``'/usr/local'``. The
+ returned string points into static storage; the caller should not modify its
+ value. This corresponds to the :makevar:`prefix` variable in the top-level
+ :file:`Makefile` and the :option:`--prefix` argument to the :program:`configure`
+ script at build time. The value is available to Python code as ``sys.prefix``.
+ It is only useful on Unix. See also the next function.
+
+
+.. cfunction:: char* Py_GetExecPrefix()
+
+ Return the *exec-prefix* for installed platform-*dependent* files. This is
+ derived through a number of complicated rules from the program name set with
+ :cfunc:`Py_SetProgramName` and some environment variables; for example, if the
+ program name is ``'/usr/local/bin/python'``, the exec-prefix is
+ ``'/usr/local'``. The returned string points into static storage; the caller
+ should not modify its value. This corresponds to the :makevar:`exec_prefix`
+ variable in the top-level :file:`Makefile` and the :option:`--exec-prefix`
+ argument to the :program:`configure` script at build time. The value is
+ available to Python code as ``sys.exec_prefix``. 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 :file:`/usr/local/plat` subtree while platform independent may
+ be installed in :file:`/usr/local`.
+
+ 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 :program:`mount` or
+ :program:`automount` programs to share :file:`/usr/local` between platforms
+ while having :file:`/usr/local/plat` be a different filesystem for each
+ platform.
+
+
+.. cfunction:: char* Py_GetProgramFullPath()
+
+ .. index::
+ single: Py_SetProgramName()
+ single: executable (in module sys)
+
+ 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 :cfunc:`Py_SetProgramName` above). The returned string points into
+ static storage; the caller should not modify its value. The value is available
+ to Python code as ``sys.executable``.
+
+
+.. cfunction:: char* Py_GetPath()
+
+ .. index::
+ triple: module; search; path
+ single: path (in module sys)
+
+ Return the default module search path; this is computed from the program name
+ (set by :cfunc:`Py_SetProgramName` 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 ``':'`` on Unix and
+ Mac OS X, ``';'`` on Windows. The returned string points into static storage;
+ the caller should not modify its value. The value is available to Python code
+ as the list ``sys.path``, which may be modified to change the future search path
+ for loaded modules.
+
+ .. XXX should give the exact rules
+
+
+.. cfunction:: const char* Py_GetVersion()
+
+ Return the version of this Python interpreter. This is a string that looks
+ something like ::
+
+ "1.5 (#67, Dec 31 1997, 22:34:28) [GCC 2.7.2.2]"
+
+ .. index:: single: version (in module sys)
+
+ 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 ``sys.version``.
+
+
+.. cfunction:: const char* Py_GetBuildNumber()
+
+ Return a string representing the Subversion revision that this Python executable
+ was built from. This number is a string because it may contain a trailing 'M'
+ if Python was built from a mixed revision source tree.
+
+ .. versionadded:: 2.5
+
+
+.. cfunction:: const char* Py_GetPlatform()
+
+ .. index:: single: platform (in module sys)
+
+ 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 ``'sunos5'``. On Mac OS X, it is
+ ``'darwin'``. On Windows, it is ``'win'``. The returned string points into
+ static storage; the caller should not modify its value. The value is available
+ to Python code as ``sys.platform``.
+
+
+.. cfunction:: const char* Py_GetCopyright()
+
+ Return the official copyright string for the current Python version, for example
+
+ ``'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'``
+
+ .. index:: single: copyright (in module sys)
+
+ The returned string points into static storage; the caller should not modify its
+ value. The value is available to Python code as ``sys.copyright``.
+
+
+.. cfunction:: const char* Py_GetCompiler()
+
+ Return an indication of the compiler used to build the current Python version,
+ in square brackets, for example::
+
+ "[GCC 2.7.2.2]"
+
+ .. index:: single: version (in module sys)
+
+ 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
+ ``sys.version``.
+
+
+.. cfunction:: const char* Py_GetBuildInfo()
+
+ Return information about the sequence number and build date and time of the
+ current Python interpreter instance, for example ::
+
+ "#67, Aug 1 1997, 22:34:28"
+
+ .. index:: single: version (in module sys)
+
+ 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
+ ``sys.version``.
+
+
+.. cfunction:: void PySys_SetArgv(int argc, char **argv)
+
+ .. index::
+ single: main()
+ single: Py_FatalError()
+ single: argv (in module sys)
+
+ Set ``sys.argv`` based on *argc* and *argv*. These parameters are similar to
+ those passed to the program's :cfunc:`main` 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 ``sys.argv``, a fatal condition is signalled using
+ :cfunc:`Py_FatalError`.
+
+ .. XXX impl. doesn't seem consistent in allowing 0/NULL for the params;
+ check w/ Guido.
+
+
+.. _threads:
+
+Thread State and the Global Interpreter Lock
+============================================
+
+.. index::
+ single: global interpreter lock
+ single: interpreter lock
+ single: lock, interpreter
+
+The Python interpreter is not fully thread safe. In order to support
+multi-threaded Python programs, there's a global lock 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.
+
+.. index:: single: setcheckinterval() (in module sys)
+
+Therefore, the rule exists that only the thread that has acquired the global
+interpreter lock may operate on Python objects or call Python/C API functions.
+In order to support multi-threaded Python programs, the interpreter regularly
+releases and reacquires the lock --- by default, every 100 bytecode instructions
+(this can be changed with :func:`sys.setcheckinterval`). The lock is also
+released and reacquired around potentially blocking I/O operations like reading
+or writing a file, so that other threads can run while the thread that requests
+the I/O is waiting for the I/O operation to complete.
+
+.. index::
+ single: PyThreadState
+ single: PyThreadState
+
+The Python interpreter needs to keep some bookkeeping information separate per
+thread --- for this it uses a data structure called :ctype:`PyThreadState`.
+There's one global variable, however: the pointer to the current
+:ctype:`PyThreadState` structure. While most thread packages have a way to
+store "per-thread global data," Python's internal platform independent thread
+abstraction doesn't support this yet. Therefore, the current thread state must
+be manipulated explicitly.
+
+This is easy enough in most cases. Most code manipulating the global
+interpreter lock has the following simple structure::
+
+ Save the thread state in a local variable.
+ Release the interpreter lock.
+ ...Do some blocking I/O operation...
+ Reacquire the interpreter lock.
+ Restore the thread state from the local variable.
+
+This is so common that a pair of macros exists to simplify it::
+
+ Py_BEGIN_ALLOW_THREADS
+ ...Do some blocking I/O operation...
+ Py_END_ALLOW_THREADS
+
+.. index::
+ single: Py_BEGIN_ALLOW_THREADS
+ single: Py_END_ALLOW_THREADS
+
+The :cmacro:`Py_BEGIN_ALLOW_THREADS` macro opens a new block and declares a
+hidden local variable; the :cmacro:`Py_END_ALLOW_THREADS` macro closes the
+block. Another advantage of using these two macros is that when Python is
+compiled without thread support, they are defined empty, thus saving the thread
+state and lock manipulations.
+
+When thread support is enabled, the block above expands to the following code::
+
+ PyThreadState *_save;
+
+ _save = PyEval_SaveThread();
+ ...Do some blocking I/O operation...
+ PyEval_RestoreThread(_save);
+
+Using even lower level primitives, we can get roughly the same effect as
+follows::
+
+ PyThreadState *_save;
+
+ _save = PyThreadState_Swap(NULL);
+ PyEval_ReleaseLock();
+ ...Do some blocking I/O operation...
+ PyEval_AcquireLock();
+ PyThreadState_Swap(_save);
+
+.. index::
+ single: PyEval_RestoreThread()
+ single: errno
+ single: PyEval_SaveThread()
+ single: PyEval_ReleaseLock()
+ single: PyEval_AcquireLock()
+
+There are some subtle differences; in particular, :cfunc:`PyEval_RestoreThread`
+saves and restores the value of the global variable :cdata:`errno`, since the
+lock manipulation does not guarantee that :cdata:`errno` is left alone. Also,
+when thread support is disabled, :cfunc:`PyEval_SaveThread` and
+:cfunc:`PyEval_RestoreThread` don't manipulate the lock; in this case,
+:cfunc:`PyEval_ReleaseLock` and :cfunc:`PyEval_AcquireLock` are not available.
+This is done so that dynamically loaded extensions compiled with thread support
+enabled can be loaded by an interpreter that was compiled with disabled thread
+support.
+
+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.
+
+Why am I going on with so much detail about this? Because when threads are
+created from C, they don't have the global interpreter lock, nor is there a
+thread state data structure for them. Such threads must bootstrap themselves
+into existence, by first creating a thread state data structure, then acquiring
+the lock, and finally storing their thread state pointer, before they can start
+using the Python/C API. When they are done, they should reset the thread state
+pointer, release the lock, and finally free their thread state data structure.
+
+Beginning with version 2.3, threads can now take advantage of the
+:cfunc:`PyGILState_\*` functions to do all of the above automatically. The
+typical idiom for calling into Python from a C thread is now::
+
+ PyGILState_STATE gstate;
+ gstate = PyGILState_Ensure();
+
+ /* Perform Python actions here. */
+ result = CallSomeFunction();
+ /* evaluate result */
+
+ /* Release the thread. No Python API allowed beyond this point. */
+ PyGILState_Release(gstate);
+
+Note that the :cfunc:`PyGILState_\*` functions assume there is only one global
+interpreter (created automatically by :cfunc:`Py_Initialize`). Python still
+supports the creation of additional interpreters (using
+:cfunc:`Py_NewInterpreter`), but mixing multiple interpreters and the
+:cfunc:`PyGILState_\*` API is unsupported.
+
+
+.. ctype:: PyInterpreterState
+
+ 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.
+
+
+.. ctype:: PyThreadState
+
+ This data structure represents the state of a single thread. The only public
+ data member is :ctype:`PyInterpreterState \*`:attr:`interp`, which points to
+ this thread's interpreter state.
+
+
+.. cfunction:: void PyEval_InitThreads()
+
+ .. index::
+ single: PyEval_ReleaseLock()
+ single: PyEval_ReleaseThread()
+ single: PyEval_SaveThread()
+ single: PyEval_RestoreThread()
+
+ 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 :cfunc:`PyEval_ReleaseLock` or
+ ``PyEval_ReleaseThread(tstate)``. It is not needed before calling
+ :cfunc:`PyEval_SaveThread` or :cfunc:`PyEval_RestoreThread`.
+
+ .. index:: single: Py_Initialize()
+
+ This is a no-op when called for a second time. It is safe to call this function
+ before calling :cfunc:`Py_Initialize`.
+
+ .. index:: module: thread
+
+ When only the main thread exists, no lock 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 lock, it also acquires it. Before the Python
+ :mod:`thread` module creates a new thread, knowing that either it has the lock
+ or the lock hasn't been created yet, it calls :cfunc:`PyEval_InitThreads`. 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.
+
+
+.. cfunction:: int PyEval_ThreadsInitialized()
+
+ Returns a non-zero value if :cfunc:`PyEval_InitThreads` has been called. This
+ function can be called without holding the lock, 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.
+
+ .. versionadded:: 2.4
+
+
+.. cfunction:: void PyEval_AcquireLock()
+
+ Acquire the global interpreter lock. The lock must have been created earlier.
+ If this thread already has the lock, a deadlock ensues. This function is not
+ available when thread support is disabled at compile time.
+
+
+.. cfunction:: void PyEval_ReleaseLock()
+
+ Release the global interpreter lock. The lock must have been created earlier.
+ This function is not available when thread support is disabled at compile time.
+
+
+.. cfunction:: void PyEval_AcquireThread(PyThreadState *tstate)
+
+ 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. This function is not
+ available when thread support is disabled at compile time.
+
+
+.. cfunction:: void PyEval_ReleaseThread(PyThreadState *tstate)
+
+ 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. This function is not available when thread support is disabled at
+ compile time.
+
+
+.. cfunction:: PyThreadState* PyEval_SaveThread()
+
+ Release the 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.)
+
+
+.. cfunction:: void PyEval_RestoreThread(PyThreadState *tstate)
+
+ Acquire the 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.)
+
+
+.. cfunction:: void PyEval_ReInitThreads()
+
+ This function is called from :cfunc:`PyOS_AfterFork` to ensure that newly
+ created child processes don't hold locks referring to threads which
+ are not running in the child process.
+
+
+The following macros are normally used without a trailing semicolon; look for
+example usage in the Python source distribution.
+
+
+.. cmacro:: Py_BEGIN_ALLOW_THREADS
+
+ This macro expands to ``{ PyThreadState *_save; _save = PyEval_SaveThread();``.
+ Note that it contains an opening brace; it must be matched with a following
+ :cmacro:`Py_END_ALLOW_THREADS` macro. See above for further discussion of this
+ macro. It is a no-op when thread support is disabled at compile time.
+
+
+.. cmacro:: Py_END_ALLOW_THREADS
+
+ This macro expands to ``PyEval_RestoreThread(_save); }``. Note that it contains
+ a closing brace; it must be matched with an earlier
+ :cmacro:`Py_BEGIN_ALLOW_THREADS` macro. See above for further discussion of
+ this macro. It is a no-op when thread support is disabled at compile time.
+
+
+.. cmacro:: Py_BLOCK_THREADS
+
+ This macro expands to ``PyEval_RestoreThread(_save);``: it is equivalent to
+ :cmacro:`Py_END_ALLOW_THREADS` without the closing brace. It is a no-op when
+ thread support is disabled at compile time.
+
+
+.. cmacro:: Py_UNBLOCK_THREADS
+
+ This macro expands to ``_save = PyEval_SaveThread();``: it is equivalent to
+ :cmacro:`Py_BEGIN_ALLOW_THREADS` without the opening brace and variable
+ declaration. It is a no-op when thread support is disabled at compile time.
+
+All of the following functions are only available when thread support is enabled
+at compile time, and must be called only when the interpreter lock has been
+created.
+
+
+.. cfunction:: PyInterpreterState* PyInterpreterState_New()
+
+ Create a new interpreter state object. The interpreter lock need not be held,
+ but may be held if it is necessary to serialize calls to this function.
+
+
+.. cfunction:: void PyInterpreterState_Clear(PyInterpreterState *interp)
+
+ Reset all information in an interpreter state object. The interpreter lock must
+ be held.
+
+
+.. cfunction:: void PyInterpreterState_Delete(PyInterpreterState *interp)
+
+ Destroy an interpreter state object. The interpreter lock need not be held.
+ The interpreter state must have been reset with a previous call to
+ :cfunc:`PyInterpreterState_Clear`.
+
+
+.. cfunction:: PyThreadState* PyThreadState_New(PyInterpreterState *interp)
+
+ Create a new thread state object belonging to the given interpreter object. The
+ interpreter lock need not be held, but may be held if it is necessary to
+ serialize calls to this function.
+
+
+.. cfunction:: void PyThreadState_Clear(PyThreadState *tstate)
+
+ Reset all information in a thread state object. The interpreter lock must be
+ held.
+
+
+.. cfunction:: void PyThreadState_Delete(PyThreadState *tstate)
+
+ Destroy a thread state object. The interpreter lock need not be held. The
+ thread state must have been reset with a previous call to
+ :cfunc:`PyThreadState_Clear`.
+
+
+.. cfunction:: PyThreadState* PyThreadState_Get()
+
+ Return the current thread state. The 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*).
+
+
+.. cfunction:: PyThreadState* PyThreadState_Swap(PyThreadState *tstate)
+
+ Swap the current thread state with the thread state given by the argument
+ *tstate*, which may be *NULL*. The interpreter lock must be held.
+
+
+.. cfunction:: PyObject* PyThreadState_GetDict()
+
+ 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.
+
+ .. versionchanged:: 2.3
+ Previously this could only be called when a current thread is active, and *NULL*
+ meant that an exception was raised.
+
+
+.. cfunction:: int PyThreadState_SetAsyncExc(long id, PyObject *exc)
+
+ 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 :const:`NULL`, the pending
+ exception (if any) for the thread is cleared. This raises no exceptions.
+
+ .. versionadded:: 2.3
+
+
+.. cfunction:: PyGILState_STATE PyGILState_Ensure()
+
+ Ensure that the current thread is ready to call the Python C API regardless of
+ the current state of Python, or of its thread lock. This may be called as many
+ times as desired by a thread as long as each call is matched with a call to
+ :cfunc:`PyGILState_Release`. In general, other thread-related APIs may be used
+ between :cfunc:`PyGILState_Ensure` and :cfunc:`PyGILState_Release` calls as long
+ as the thread state is restored to its previous state before the Release(). For
+ example, normal usage of the :cmacro:`Py_BEGIN_ALLOW_THREADS` and
+ :cmacro:`Py_END_ALLOW_THREADS` macros is acceptable.
+
+ The return value is an opaque "handle" to the thread state when
+ :cfunc:`PyGILState_Ensure` was called, and must be passed to
+ :cfunc:`PyGILState_Release` to ensure Python is left in the same state. Even
+ though recursive calls are allowed, these handles *cannot* be shared - each
+ unique call to :cfunc:`PyGILState_Ensure` must save the handle for its call
+ to :cfunc:`PyGILState_Release`.
+
+ When the function returns, the current thread will hold the GIL. Failure is a
+ fatal error.
+
+ .. versionadded:: 2.3
+
+
+.. cfunction:: void PyGILState_Release(PyGILState_STATE)
+
+ Release any resources previously acquired. After this call, Python's state will
+ be the same as it was prior to the corresponding :cfunc:`PyGILState_Ensure` call
+ (but generally this state will be unknown to the caller, hence the use of the
+ GILState API.)
+
+ Every call to :cfunc:`PyGILState_Ensure` must be matched by a call to
+ :cfunc:`PyGILState_Release` on the same thread.
+
+ .. versionadded:: 2.3
+
+
+.. _profiling:
+
+Profiling and Tracing
+=====================
+
+.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
+
+
+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.
+
+
+.. ctype:: int (*Py_tracefunc)(PyObject *obj, PyFrameObject *frame, int what, PyObject *arg)
+
+ The type of the trace function registered using :cfunc:`PyEval_SetProfile` and
+ :cfunc:`PyEval_SetTrace`. 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 :const:`PyTrace_CALL`,
+ :const:`PyTrace_EXCEPTION`, :const:`PyTrace_LINE`, :const:`PyTrace_RETURN`,
+ :const:`PyTrace_C_CALL`, :const:`PyTrace_C_EXCEPTION`, or
+ :const:`PyTrace_C_RETURN`, and *arg* depends on the value of *what*:
+
+ +------------------------------+--------------------------------------+
+ | Value of *what* | Meaning of *arg* |
+ +==============================+======================================+
+ | :const:`PyTrace_CALL` | Always *NULL*. |
+ +------------------------------+--------------------------------------+
+ | :const:`PyTrace_EXCEPTION` | Exception information as returned by |
+ | | :func:`sys.exc_info`. |
+ +------------------------------+--------------------------------------+
+ | :const:`PyTrace_LINE` | Always *NULL*. |
+ +------------------------------+--------------------------------------+
+ | :const:`PyTrace_RETURN` | Value being returned to the caller. |
+ +------------------------------+--------------------------------------+
+ | :const:`PyTrace_C_CALL` | Name of function being called. |
+ +------------------------------+--------------------------------------+
+ | :const:`PyTrace_C_EXCEPTION` | Always *NULL*. |
+ +------------------------------+--------------------------------------+
+ | :const:`PyTrace_C_RETURN` | Always *NULL*. |
+ +------------------------------+--------------------------------------+
+
+
+.. cvar:: int PyTrace_CALL
+
+ The value of the *what* parameter to a :ctype:`Py_tracefunc` 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.
+
+
+.. cvar:: int PyTrace_EXCEPTION
+
+ The value of the *what* parameter to a :ctype:`Py_tracefunc` 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.
+
+
+.. cvar:: int PyTrace_LINE
+
+ The value passed as the *what* parameter to a trace function (but not a
+ profiling function) when a line-number event is being reported.
+
+
+.. cvar:: int PyTrace_RETURN
+
+ The value for the *what* parameter to :ctype:`Py_tracefunc` functions when a
+ call is returning without propagating an exception.
+
+
+.. cvar:: int PyTrace_C_CALL
+
+ The value for the *what* parameter to :ctype:`Py_tracefunc` functions when a C
+ function is about to be called.
+
+
+.. cvar:: int PyTrace_C_EXCEPTION
+
+ The value for the *what* parameter to :ctype:`Py_tracefunc` functions when a C
+ function has thrown an exception.
+
+
+.. cvar:: int PyTrace_C_RETURN
+
+ The value for the *what* parameter to :ctype:`Py_tracefunc` functions when a C
+ function has returned.
+
+
+.. cfunction:: void PyEval_SetProfile(Py_tracefunc func, PyObject *obj)
+
+ 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 the line-number
+ events.
+
+
+.. cfunction:: void PyEval_SetTrace(Py_tracefunc func, PyObject *obj)
+
+ Set the tracing function to *func*. This is similar to
+ :cfunc:`PyEval_SetProfile`, except the tracing function does receive line-number
+ events.
+
+.. cfunction:: PyObject* PyEval_GetCallStats(PyObject *self)
+
+ Return a tuple of function call counts. There are constants defined for the
+ positions within the tuple:
+
+ +-------------------------------+-------+
+ | Name | Value |
+ +===============================+=======+
+ | :const:`PCALL_ALL` | 0 |
+ +-------------------------------+-------+
+ | :const:`PCALL_FUNCTION` | 1 |
+ +-------------------------------+-------+
+ | :const:`PCALL_FAST_FUNCTION` | 2 |
+ +-------------------------------+-------+
+ | :const:`PCALL_FASTER_FUNCTION`| 3 |
+ +-------------------------------+-------+
+ | :const:`PCALL_METHOD` | 4 |
+ +-------------------------------+-------+
+ | :const:`PCALL_BOUND_METHOD` | 5 |
+ +-------------------------------+-------+
+ | :const:`PCALL_CFUNCTION` | 6 |
+ +-------------------------------+-------+
+ | :const:`PCALL_TYPE` | 7 |
+ +-------------------------------+-------+
+ | :const:`PCALL_GENERATOR` | 8 |
+ +-------------------------------+-------+
+ | :const:`PCALL_OTHER` | 9 |
+ +-------------------------------+-------+
+ | :const:`PCALL_POP` | 10 |
+ +-------------------------------+-------+
+
+ :const:`PCALL_FAST_FUNCTION` means no argument tuple needs to be created.
+ :const:`PCALL_FASTER_FUNCTION` 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 :const:`CALL_PROFILE`
+ defined.
+
+.. _advanced-debugging:
+
+Advanced Debugger Support
+=========================
+
+.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
+
+
+These functions are only intended to be used by advanced debugging tools.
+
+
+.. cfunction:: PyInterpreterState* PyInterpreterState_Head()
+
+ Return the interpreter state object at the head of the list of all such objects.
+
+ .. versionadded:: 2.2
+
+
+.. cfunction:: PyInterpreterState* PyInterpreterState_Next(PyInterpreterState *interp)
+
+ Return the next interpreter state object after *interp* from the list of all
+ such objects.
+
+ .. versionadded:: 2.2
+
+
+.. cfunction:: PyThreadState * PyInterpreterState_ThreadHead(PyInterpreterState *interp)
+
+ Return the a pointer to the first :ctype:`PyThreadState` object in the list of
+ threads associated with the interpreter *interp*.
+
+ .. versionadded:: 2.2
+
+
+.. cfunction:: PyThreadState* PyThreadState_Next(PyThreadState *tstate)
+
+ Return the next thread state object after *tstate* from the list of all such
+ objects belonging to the same :ctype:`PyInterpreterState` object.
+
+ .. versionadded:: 2.2
+