| .. 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: builtins |
| module: __main__ |
| module: sys |
| triple: module; search; path |
| single: PySys_SetArgv() |
| single: PySys_SetArgvEx() |
| 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:`builtins`, :mod:`__main__` and :mod:`sys`. It also initializes |
| the module search path (``sys.path``). It does not set ``sys.argv``; use |
| :cfunc:`PySys_SetArgvEx` 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. |
| |
| |
| .. 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: builtins |
| 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:`builtins`, :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(wchar_t *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 |
| (converted to wide characters). |
| 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 wide 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:: wchar* 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:: wchar_t* 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:: wchar_t* 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:: wchar_t* 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:: wchar_t* 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 list |
| :data:`sys.path` is initialized with this value on interpreter startup; it |
| can be (and usually is) modified later to change the search path for loading |
| 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 :: |
| |
| "3.0a5+ (py3k:63103M, May 12 2008, 00:53:55) \n[GCC 4.2.3]" |
| |
| .. 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 :data:`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. |
| |
| |
| .. 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_SetArgvEx(int argc, wchar_t **argv, int updatepath) |
| |
| .. index:: |
| single: main() |
| single: Py_FatalError() |
| single: argv (in module sys) |
| |
| Set :data:`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 :data:`sys.argv`, a fatal |
| condition is signalled using :cfunc:`Py_FatalError`. |
| |
| If *updatepath* is zero, this is all the function does. If *updatepath* |
| is non-zero, the function also modifies :data:`sys.path` according to the |
| following algorithm: |
| |
| - If the name of an existing script is passed in ``argv[0]``, the absolute |
| path of the directory where the script is located is prepended to |
| :data:`sys.path`. |
| - Otherwise (that is, if *argc* is 0 or ``argv[0]`` doesn't point |
| to an existing file name), an empty string is prepended to |
| :data:`sys.path`, which is the same as prepending the current working |
| directory (``"."``). |
| |
| .. note:: |
| It is recommended that applications embedding the Python interpreter |
| for purposes other than executing a single script pass 0 as *updatepath*, |
| and update :data:`sys.path` themselves if desired. |
| See `CVE-2008-5983 <http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983>`_. |
| |
| On versions before 3.1.3, you can achieve the same effect by manually |
| popping the first :data:`sys.path` element after having called |
| :cfunc:`PySys_SetArgv`, for example using:: |
| |
| PyRun_SimpleString("import sys; sys.path.pop(0)\n"); |
| |
| .. versionadded:: 3.1.3 |
| |
| .. XXX impl. doesn't seem consistent in allowing 0/NULL for the params; |
| check w/ Guido. |
| |
| |
| .. cfunction:: void PySys_SetArgv(int argc, wchar_t **argv) |
| |
| This function works like :cfunc:`PySys_SetArgvEx` with *updatepath* set to 1. |
| |
| |
| .. cfunction:: void Py_SetPythonHome(wchar_t *home) |
| |
| Set the default "home" directory, that is, the location of the standard |
| Python libraries. The libraries are searched in |
| :file:`{home}/lib/python{version}` and :file:`{home}/lib/python{version}`. |
| 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:: w_char* Py_GetPythonHome() |
| |
| Return the default "home", that is, the value set by a previous call to |
| :cfunc:`Py_SetPythonHome`, or the value of the :envvar:`PYTHONHOME` |
| environment variable if it is set. |
| |
| |
| .. _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, called the :dfn:`global |
| interpreter lock` or :dfn:`GIL`, 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. Before the addition of :dfn:`thread-local |
| storage` (:dfn:`TLS`) the current thread state had to 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 global interpreter lock. |
| ...Do some blocking I/O operation... |
| Reacquire the global 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 GIL 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 GIL; 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. |
| |
| It is important to note that 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. |
| |
| Threads can 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. |
| |
| Another important thing to note about threads is their behaviour in the face |
| of the C :cfunc:`fork` call. On most systems with :cfunc:`fork`, 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 :func:`os.fork` by acquiring the locks it uses internally before |
| the fork, and releasing them afterwards. In addition, it resets any |
| :ref:`lock-objects` 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 |
| :cfunc:`posix_atfork` would need to be used to accomplish the same thing. |
| Additionally, when extending or embedding Python, calling :cfunc:`fork` |
| directly rather than through :func:`os.fork` (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. |
| :cfunc:`PyOS_AfterFork` tries to reset the necessary locks, but is not |
| always able to. |
| |
| .. 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 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 :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 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. |
| |
| |
| .. 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 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.) |
| |
| |
| .. cfunction:: void PyEval_RestoreThread(PyThreadState *tstate) |
| |
| 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.) |
| |
| |
| .. 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 global interpreter lock has |
| been created. |
| |
| |
| .. cfunction:: PyInterpreterState* PyInterpreterState_New() |
| |
| 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. |
| |
| |
| .. cfunction:: void PyInterpreterState_Clear(PyInterpreterState *interp) |
| |
| Reset all information in an interpreter state object. The global interpreter |
| lock must be held. |
| |
| |
| .. cfunction:: void PyInterpreterState_Delete(PyInterpreterState *interp) |
| |
| 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 |
| :cfunc:`PyInterpreterState_Clear`. |
| |
| |
| .. cfunction:: PyThreadState* PyThreadState_New(PyInterpreterState *interp) |
| |
| 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. |
| |
| |
| .. cfunction:: void PyThreadState_Clear(PyThreadState *tstate) |
| |
| Reset all information in a thread state object. The global interpreter lock |
| must be held. |
| |
| |
| .. cfunction:: void PyThreadState_Delete(PyThreadState *tstate) |
| |
| 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 |
| :cfunc:`PyThreadState_Clear`. |
| |
| |
| .. cfunction:: PyThreadState* PyThreadState_Get() |
| |
| 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*). |
| |
| |
| .. 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 global 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. |
| |
| |
| .. 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. |
| |
| |
| .. 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 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 :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. |
| |
| |
| .. 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. |
| |
| |
| |
| Asynchronous Notifications |
| ========================== |
| |
| 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 argument. |
| |
| .. index:: single: setcheckinterval() (in module sys) |
| |
| Every check interval, when the global interpreter lock is released and |
| reacquired, Python will also call any such provided functions. This can be used |
| for example by asynchronous IO handlers. The notification can be scheduled from |
| a worker thread and the actual call than made at the earliest convenience by the |
| main thread where it has possession of the global interpreter lock and can |
| perform any Python API calls. |
| |
| .. cfunction:: void Py_AddPendingCall( int (*func)(void *, void *arg) ) |
| |
| .. index:: single: Py_AddPendingCall() |
| |
| Post a notification to the Python main thread. If successful, *func* will be |
| called with the argument *arg* at the earliest convenience. *func* will be |
| called having the global interpreter lock held and can thus use the full |
| Python API and can take any action such as setting object attributes to |
| signal IO completion. It must return 0 on success, or -1 signalling an |
| exception. The notification function 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, for example, if it |
| calls back into Python code. |
| |
| This function returns 0 on success in which case the notification has been |
| scheduled. Otherwise, for example if the notification buffer is full, it |
| returns -1 without setting any exception. |
| |
| This function can be called on any thread, be it a Python thread or some |
| other system thread. If it is a Python thread, it doesn't matter if it holds |
| the global interpreter lock or not. |
| |
| .. versionadded:: 3.1 |
| |
| |
| .. _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. |
| |
| 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. |
| |
| |
| .. cfunction:: PyInterpreterState* PyInterpreterState_Next(PyInterpreterState *interp) |
| |
| Return the next interpreter state object after *interp* from the list of all |
| such objects. |
| |
| |
| .. 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*. |
| |
| |
| .. 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. |
| |