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Diffstat (limited to 'Doc/c-api/init.rst')
| -rw-r--r-- | Doc/c-api/init.rst | 271 |
1 files changed, 73 insertions, 198 deletions
diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst index 52f64a61006..409539dec17 100644 --- a/Doc/c-api/init.rst +++ b/Doc/c-api/init.rst @@ -77,10 +77,7 @@ The following functions can be safely called before Python is initialized: Despite their apparent similarity to some of the functions listed above, the following functions **should not be called** before the interpreter has - been initialized: :c:func:`Py_EncodeLocale`, :c:func:`Py_GetPath`, - :c:func:`Py_GetPrefix`, :c:func:`Py_GetExecPrefix`, - :c:func:`Py_GetProgramFullPath`, :c:func:`Py_GetPythonHome`, - :c:func:`Py_GetProgramName`, :c:func:`PyEval_InitThreads`, and + been initialized: :c:func:`Py_EncodeLocale`, :c:func:`PyEval_InitThreads`, and :c:func:`Py_RunMain`. @@ -145,9 +142,6 @@ to 1 and ``-bb`` sets :c:data:`Py_BytesWarningFlag` to 2. :c:member:`PyConfig.pathconfig_warnings` should be used instead, see :ref:`Python Initialization Configuration <init-config>`. - Suppress error messages when calculating the module search path in - :c:func:`Py_GetPath`. - Private flag used by ``_freeze_module`` and ``frozenmain`` programs. .. deprecated-removed:: 3.12 3.15 @@ -203,7 +197,7 @@ to 1 and ``-bb`` sets :c:data:`Py_BytesWarningFlag` to 2. Set by the :option:`-i` option. - .. deprecated:: 3.12 + .. deprecated-removed:: 3.12 3.15 .. c:var:: int Py_IsolatedFlag @@ -498,17 +492,8 @@ Initializing and finalizing the interpreter strings other than those passed in (however, the contents of the strings pointed to by the argument list are not modified). - The return value will be ``0`` if the interpreter exits normally (i.e., - without an exception), ``1`` if the interpreter exits due to an exception, - or ``2`` if the argument list does not represent a valid Python command - line. - - Note that if an otherwise unhandled :exc:`SystemExit` is raised, this - function will not return ``1``, but exit the process, as long as - ``Py_InspectFlag`` is not set. If ``Py_InspectFlag`` is set, execution will - drop into the interactive Python prompt, at which point a second otherwise - unhandled :exc:`SystemExit` will still exit the process, while any other - means of exiting will set the return value as described above. + The return value is ``2`` if the argument list does not represent a valid + Python command line, and otherwise the same as :c:func:`Py_RunMain`. In terms of the CPython runtime configuration APIs documented in the :ref:`runtime configuration <init-config>` section (and without accounting @@ -545,23 +530,18 @@ Initializing and finalizing the interpreter If :c:member:`PyConfig.inspect` is not set (the default), the return value will be ``0`` if the interpreter exits normally (that is, without raising - an exception), or ``1`` if the interpreter exits due to an exception. If an - otherwise unhandled :exc:`SystemExit` is raised, the function will immediately - exit the process instead of returning ``1``. + an exception), the exit status of an unhandled :exc:`SystemExit`, or ``1`` + for any other unhandled exception. If :c:member:`PyConfig.inspect` is set (such as when the :option:`-i` option is used), rather than returning when the interpreter exits, execution will instead resume in an interactive Python prompt (REPL) using the ``__main__`` module's global namespace. If the interpreter exited with an exception, it is immediately raised in the REPL session. The function return value is - then determined by the way the *REPL session* terminates: returning ``0`` - if the session terminates without raising an unhandled exception, exiting - immediately for an unhandled :exc:`SystemExit`, and returning ``1`` for - any other unhandled exception. + then determined by the way the *REPL session* terminates: ``0``, ``1``, or + the status of a :exc:`SystemExit`, as specified above. - This function always finalizes the Python interpreter regardless of whether - it returns a value or immediately exits the process due to an unhandled - :exc:`SystemExit` exception. + This function always finalizes the Python interpreter before it returns. See :ref:`Python Configuration <init-python-config>` for an example of a customized Python that always runs in isolated mode using @@ -586,7 +566,6 @@ Process-wide parameters .. index:: single: Py_Initialize() single: main() - single: Py_GetPath() This API is kept for backward compatibility: setting :c:member:`PyConfig.program_name` should be used instead, see :ref:`Python @@ -596,7 +575,7 @@ Process-wide parameters the first time, if it is called at all. It tells the interpreter the value of the ``argv[0]`` argument to the :c:func:`main` function of the program (converted to wide characters). - This is used by :c:func:`Py_GetPath` and some other functions below to find + This is used by 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 @@ -609,146 +588,6 @@ Process-wide parameters .. deprecated-removed:: 3.11 3.15 -.. c:function:: wchar_t* Py_GetProgramName() - - Return the program name set with :c:member:`PyConfig.program_name`, or the default. - The returned string points into static storage; the caller should not modify its - value. - - This function should not be called before :c:func:`Py_Initialize`, otherwise - it returns ``NULL``. - - .. versionchanged:: 3.10 - It now returns ``NULL`` if called before :c:func:`Py_Initialize`. - - .. deprecated-removed:: 3.13 3.15 - Use :c:func:`PyConfig_Get("executable") <PyConfig_Get>` - (:data:`sys.executable`) instead. - - -.. c:function:: 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 - :c:member:`PyConfig.program_name` 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.base_prefix``. - It is only useful on Unix. See also the next function. - - This function should not be called before :c:func:`Py_Initialize`, otherwise - it returns ``NULL``. - - .. versionchanged:: 3.10 - It now returns ``NULL`` if called before :c:func:`Py_Initialize`. - - .. deprecated-removed:: 3.13 3.15 - Use :c:func:`PyConfig_Get("base_prefix") <PyConfig_Get>` - (:data:`sys.base_prefix`) instead. Use :c:func:`PyConfig_Get("prefix") - <PyConfig_Get>` (:data:`sys.prefix`) if :ref:`virtual environments - <venv-def>` need to be handled. - - -.. c:function:: 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 - :c:member:`PyConfig.program_name` 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 ``--exec-prefix`` - argument to the :program:`configure` script at build time. The value is - available to Python code as ``sys.base_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. - - This function should not be called before :c:func:`Py_Initialize`, otherwise - it returns ``NULL``. - - .. versionchanged:: 3.10 - It now returns ``NULL`` if called before :c:func:`Py_Initialize`. - - .. deprecated-removed:: 3.13 3.15 - Use :c:func:`PyConfig_Get("base_exec_prefix") <PyConfig_Get>` - (:data:`sys.base_exec_prefix`) instead. Use - :c:func:`PyConfig_Get("exec_prefix") <PyConfig_Get>` - (:data:`sys.exec_prefix`) if :ref:`virtual environments <venv-def>` need - to be handled. - -.. c:function:: wchar_t* Py_GetProgramFullPath() - - .. index:: - 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 :c:member:`PyConfig.program_name`). The returned string points into - static storage; the caller should not modify its value. The value is available - to Python code as ``sys.executable``. - - This function should not be called before :c:func:`Py_Initialize`, otherwise - it returns ``NULL``. - - .. versionchanged:: 3.10 - It now returns ``NULL`` if called before :c:func:`Py_Initialize`. - - .. deprecated-removed:: 3.13 3.15 - Use :c:func:`PyConfig_Get("executable") <PyConfig_Get>` - (:data:`sys.executable`) instead. - - -.. c:function:: 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 :c:member:`PyConfig.program_name`) 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 macOS, ``';'`` 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. - - This function should not be called before :c:func:`Py_Initialize`, otherwise - it returns ``NULL``. - - .. XXX should give the exact rules - - .. versionchanged:: 3.10 - It now returns ``NULL`` if called before :c:func:`Py_Initialize`. - - .. deprecated-removed:: 3.13 3.15 - Use :c:func:`PyConfig_Get("module_search_paths") <PyConfig_Get>` - (:data:`sys.path`) instead. - .. c:function:: const char* Py_GetVersion() Return the version of this Python interpreter. This is a string that looks @@ -919,23 +758,6 @@ Process-wide parameters .. deprecated-removed:: 3.11 3.15 -.. c:function:: wchar_t* Py_GetPythonHome() - - Return the default "home", that is, the value set by - :c:member:`PyConfig.home`, or the value of the :envvar:`PYTHONHOME` - environment variable if it is set. - - This function should not be called before :c:func:`Py_Initialize`, otherwise - it returns ``NULL``. - - .. versionchanged:: 3.10 - It now returns ``NULL`` if called before :c:func:`Py_Initialize`. - - .. deprecated-removed:: 3.13 3.15 - Use :c:func:`PyConfig_Get("home") <PyConfig_Get>` or the - :envvar:`PYTHONHOME` environment variable instead. - - .. _threads: Thread State and the Global Interpreter Lock @@ -1083,8 +905,36 @@ Note that the ``PyGILState_*`` functions assume there is only one global interpreter (created automatically by :c:func:`Py_Initialize`). Python supports the creation of additional interpreters (using :c:func:`Py_NewInterpreter`), but mixing multiple interpreters and the -``PyGILState_*`` API is unsupported. +``PyGILState_*`` API is unsupported. This is because :c:func:`PyGILState_Ensure` +and similar functions default to :term:`attaching <attached thread state>` a +:term:`thread state` for the main interpreter, meaning that the thread can't safely +interact with the calling subinterpreter. + +Supporting subinterpreters in non-Python threads +------------------------------------------------ + +If you would like to support subinterpreters with non-Python created threads, you +must use the ``PyThreadState_*`` API instead of the traditional ``PyGILState_*`` +API. + +In particular, you must store the interpreter state from the calling +function and pass it to :c:func:`PyThreadState_New`, which will ensure that +the :term:`thread state` is targeting the correct interpreter:: + + /* The return value of PyInterpreterState_Get() from the + function that created this thread. */ + PyInterpreterState *interp = ThreadData->interp; + PyThreadState *tstate = PyThreadState_New(interp); + PyThreadState_Swap(tstate); + + /* GIL of the subinterpreter is now held. + Perform Python actions here. */ + result = CallSomeFunction(); + /* evaluate result or handle exception */ + /* Destroy the thread state. No Python API allowed beyond this point. */ + PyThreadState_Clear(tstate); + PyThreadState_DeleteCurrent(); .. _fork-and-threads: @@ -1261,6 +1111,10 @@ code, or when embedding the Python interpreter: .. seealso: :c:func:`PyEval_ReleaseThread` + .. note:: + Similar to :c:func:`PyGILState_Ensure`, this function will hang the + thread if the runtime is finalizing. + The following functions use thread-local storage, and are not compatible with sub-interpreters: @@ -1287,10 +1141,10 @@ with sub-interpreters: When the function returns, there will be an :term:`attached thread state` and the thread will be able to call arbitrary Python code. Failure is a fatal error. - .. note:: - Calling this function from a thread when the runtime is finalizing will - hang the thread until the program exits, even if the thread was not - created by Python. Refer to + .. warning:: + Calling this function when the runtime is finalizing is unsafe. Doing + so will either hang the thread until the program ends, or fully crash + the interpreter in rare cases. Refer to :ref:`cautions-regarding-runtime-finalization` for more details. .. versionchanged:: 3.14 @@ -1307,7 +1161,6 @@ with sub-interpreters: Every call to :c:func:`PyGILState_Ensure` must be matched by a call to :c:func:`PyGILState_Release` on the same thread. - .. c:function:: PyThreadState* PyGILState_GetThisThreadState() Get the :term:`attached thread state` for this thread. May return ``NULL`` if no @@ -1315,20 +1168,30 @@ with sub-interpreters: 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. - .. seealso: :c:func:`PyThreadState_Get`` + .. note:: + This function does not account for :term:`thread states <thread state>` created + by something other than :c:func:`PyGILState_Ensure` (such as :c:func:`PyThreadState_New`). + Prefer :c:func:`PyThreadState_Get` or :c:func:`PyThreadState_GetUnchecked` + for most cases. + .. seealso: :c:func:`PyThreadState_Get`` .. c:function:: int PyGILState_Check() Return ``1`` if the current thread is holding the :term:`GIL` and ``0`` otherwise. This function can be called from any thread at any time. - Only if it has had its Python thread state initialized and currently is - holding the :term:`GIL` will it return ``1``. + Only if it has had its :term:`thread state <attached thread state>` initialized + via :c:func:`PyGILState_Ensure` will it return ``1``. This is mainly a helper/diagnostic function. It can be useful for example in callback contexts or memory allocation functions when knowing that the :term:`GIL` is locked can allow the caller to perform sensitive actions or otherwise behave differently. + .. note:: + If the current Python process has ever created a subinterpreter, this + function will *always* return ``1``. Prefer :c:func:`PyThreadState_GetUnchecked` + for most cases. + .. versionadded:: 3.4 @@ -1387,7 +1250,7 @@ All of the following functions must be called after :c:func:`Py_Initialize`. .. c:function:: void PyInterpreterState_Clear(PyInterpreterState *interp) Reset all information in an interpreter state object. There must be - an :term:`attached thread state` for the the interpreter. + an :term:`attached thread state` for the interpreter. .. audit-event:: cpython.PyInterpreterState_Clear "" c.PyInterpreterState_Clear @@ -2414,6 +2277,18 @@ The C-API provides a basic mutual exclusion lock. .. versionadded:: 3.13 +.. c:function:: int PyMutex_IsLocked(PyMutex *m) + + Returns non-zero if the mutex *m* is currently locked, zero otherwise. + + .. note:: + + This function is intended for use in assertions and debugging only and + should not be used to make concurrency control decisions, as the lock + state may change immediately after the check. + + .. versionadded:: next + .. _python-critical-section-api: Python Critical Section API |