mirror of
https://github.com/python/cpython
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1947 lines
74 KiB
ReStructuredText
1947 lines
74 KiB
ReStructuredText
.. highlight:: c
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.. _initialization:
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*****************************************
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Initialization, Finalization, and Threads
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*****************************************
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See also :ref:`Python Initialization Configuration <init-config>`.
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.. _pre-init-safe:
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Before Python Initialization
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============================
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In an application embedding Python, the :c:func:`Py_Initialize` function must
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be called before using any other Python/C API functions; with the exception of
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a few functions and the :ref:`global configuration variables
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<global-conf-vars>`.
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The following functions can be safely called before Python is initialized:
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* Configuration functions:
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* :c:func:`PyImport_AppendInittab`
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* :c:func:`PyImport_ExtendInittab`
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* :c:func:`!PyInitFrozenExtensions`
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* :c:func:`PyMem_SetAllocator`
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* :c:func:`PyMem_SetupDebugHooks`
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* :c:func:`PyObject_SetArenaAllocator`
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* :c:func:`PySys_ResetWarnOptions`
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* Informative functions:
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* :c:func:`Py_IsInitialized`
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* :c:func:`PyMem_GetAllocator`
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* :c:func:`PyObject_GetArenaAllocator`
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* :c:func:`Py_GetBuildInfo`
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* :c:func:`Py_GetCompiler`
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* :c:func:`Py_GetCopyright`
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* :c:func:`Py_GetPlatform`
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* :c:func:`Py_GetVersion`
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* Utilities:
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* :c:func:`Py_DecodeLocale`
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* Memory allocators:
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* :c:func:`PyMem_RawMalloc`
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* :c:func:`PyMem_RawRealloc`
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* :c:func:`PyMem_RawCalloc`
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* :c:func:`PyMem_RawFree`
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.. note::
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The following functions **should not be called** before
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:c:func:`Py_Initialize`: :c:func:`Py_EncodeLocale`, :c:func:`Py_GetPath`,
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:c:func:`Py_GetPrefix`, :c:func:`Py_GetExecPrefix`,
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:c:func:`Py_GetProgramFullPath`, :c:func:`Py_GetPythonHome`,
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and :c:func:`Py_GetProgramName`.
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.. _global-conf-vars:
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Global configuration variables
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==============================
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Python has variables for the global configuration to control different features
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and options. By default, these flags are controlled by :ref:`command line
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options <using-on-interface-options>`.
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When a flag is set by an option, the value of the flag is the number of times
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that the option was set. For example, ``-b`` sets :c:data:`Py_BytesWarningFlag`
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to 1 and ``-bb`` sets :c:data:`Py_BytesWarningFlag` to 2.
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.. c:var:: int Py_BytesWarningFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.bytes_warning` should be used instead, see :ref:`Python
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Initialization Configuration <init-config>`.
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Issue a warning when comparing :class:`bytes` or :class:`bytearray` with
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:class:`str` or :class:`bytes` with :class:`int`. Issue an error if greater
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or equal to ``2``.
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Set by the :option:`-b` option.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_DebugFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.parser_debug` should be used instead, see :ref:`Python
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Initialization Configuration <init-config>`.
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Turn on parser debugging output (for expert only, depending on compilation
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options).
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Set by the :option:`-d` option and the :envvar:`PYTHONDEBUG` environment
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variable.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_DontWriteBytecodeFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.write_bytecode` should be used instead, see :ref:`Python
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Initialization Configuration <init-config>`.
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If set to non-zero, Python won't try to write ``.pyc`` files on the
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import of source modules.
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Set by the :option:`-B` option and the :envvar:`PYTHONDONTWRITEBYTECODE`
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environment variable.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_FrozenFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.pathconfig_warnings` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Suppress error messages when calculating the module search path in
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:c:func:`Py_GetPath`.
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Private flag used by ``_freeze_module`` and ``frozenmain`` programs.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_HashRandomizationFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.hash_seed` and :c:member:`PyConfig.use_hash_seed` should
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be used instead, see :ref:`Python Initialization Configuration
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<init-config>`.
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Set to ``1`` if the :envvar:`PYTHONHASHSEED` environment variable is set to
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a non-empty string.
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If the flag is non-zero, read the :envvar:`PYTHONHASHSEED` environment
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variable to initialize the secret hash seed.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_IgnoreEnvironmentFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.use_environment` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Ignore all :envvar:`!PYTHON*` environment variables, e.g.
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:envvar:`PYTHONPATH` and :envvar:`PYTHONHOME`, that might be set.
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Set by the :option:`-E` and :option:`-I` options.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_InspectFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.inspect` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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When a script is passed as first argument or the :option:`-c` option is used,
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enter interactive mode after executing the script or the command, even when
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:data:`sys.stdin` does not appear to be a terminal.
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Set by the :option:`-i` option and the :envvar:`PYTHONINSPECT` environment
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variable.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_InteractiveFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.interactive` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Set by the :option:`-i` option.
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.. deprecated:: 3.12
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.. c:var:: int Py_IsolatedFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.isolated` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Run Python in isolated mode. In isolated mode :data:`sys.path` contains
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neither the script's directory nor the user's site-packages directory.
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Set by the :option:`-I` option.
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.. versionadded:: 3.4
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_LegacyWindowsFSEncodingFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyPreConfig.legacy_windows_fs_encoding` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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If the flag is non-zero, use the ``mbcs`` encoding with ``replace`` error
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handler, instead of the UTF-8 encoding with ``surrogatepass`` error handler,
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for the :term:`filesystem encoding and error handler`.
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Set to ``1`` if the :envvar:`PYTHONLEGACYWINDOWSFSENCODING` environment
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variable is set to a non-empty string.
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See :pep:`529` for more details.
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.. availability:: Windows.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_LegacyWindowsStdioFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.legacy_windows_stdio` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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If the flag is non-zero, use :class:`io.FileIO` instead of
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:class:`!io._WindowsConsoleIO` for :mod:`sys` standard streams.
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Set to ``1`` if the :envvar:`PYTHONLEGACYWINDOWSSTDIO` environment
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variable is set to a non-empty string.
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See :pep:`528` for more details.
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.. availability:: Windows.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_NoSiteFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.site_import` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Disable the import of the module :mod:`site` and the site-dependent
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manipulations of :data:`sys.path` that it entails. Also disable these
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manipulations if :mod:`site` is explicitly imported later (call
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:func:`site.main` if you want them to be triggered).
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Set by the :option:`-S` option.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_NoUserSiteDirectory
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.user_site_directory` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Don't add the :data:`user site-packages directory <site.USER_SITE>` to
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:data:`sys.path`.
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Set by the :option:`-s` and :option:`-I` options, and the
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:envvar:`PYTHONNOUSERSITE` environment variable.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_OptimizeFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.optimization_level` should be used instead, see
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:ref:`Python Initialization Configuration <init-config>`.
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Set by the :option:`-O` option and the :envvar:`PYTHONOPTIMIZE` environment
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variable.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_QuietFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.quiet` should be used instead, see :ref:`Python
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Initialization Configuration <init-config>`.
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Don't display the copyright and version messages even in interactive mode.
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Set by the :option:`-q` option.
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.. versionadded:: 3.2
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_UnbufferedStdioFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.buffered_stdio` should be used instead, see :ref:`Python
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Initialization Configuration <init-config>`.
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Force the stdout and stderr streams to be unbuffered.
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Set by the :option:`-u` option and the :envvar:`PYTHONUNBUFFERED`
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environment variable.
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.. deprecated-removed:: 3.12 3.14
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.. c:var:: int Py_VerboseFlag
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This API is kept for backward compatibility: setting
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:c:member:`PyConfig.verbose` should be used instead, see :ref:`Python
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Initialization Configuration <init-config>`.
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Print a message each time a module is initialized, showing the place
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(filename or built-in module) from which it is loaded. If greater or equal
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to ``2``, print a message for each file that is checked for when
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searching for a module. Also provides information on module cleanup at exit.
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Set by the :option:`-v` option and the :envvar:`PYTHONVERBOSE` environment
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variable.
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.. deprecated-removed:: 3.12 3.14
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Initializing and finalizing the interpreter
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===========================================
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.. c:function:: void Py_Initialize()
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.. index::
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single: modules (in module sys)
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single: path (in module sys)
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pair: module; builtins
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pair: module; __main__
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pair: module; sys
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triple: module; search; path
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single: Py_FinalizeEx()
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Initialize the Python interpreter. In an application embedding Python,
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this should be called before using any other Python/C API functions; see
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:ref:`Before Python Initialization <pre-init-safe>` for the few exceptions.
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This initializes
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the table of loaded modules (``sys.modules``), and creates the fundamental
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modules :mod:`builtins`, :mod:`__main__` and :mod:`sys`. It also initializes
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the module search path (``sys.path``). It does not set ``sys.argv``; use
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the new :c:type:`PyConfig` API of the :ref:`Python Initialization
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Configuration <init-config>` for that. This is a no-op when called for a
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second time
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(without calling :c:func:`Py_FinalizeEx` first). There is no return value; it is a
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fatal error if the initialization fails.
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Use the :c:func:`Py_InitializeFromConfig` function to customize the
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:ref:`Python Initialization Configuration <init-config>`.
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.. note::
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On Windows, changes the console mode from ``O_TEXT`` to ``O_BINARY``, which will
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also affect non-Python uses of the console using the C Runtime.
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.. c:function:: void Py_InitializeEx(int initsigs)
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This function works like :c:func:`Py_Initialize` if *initsigs* is ``1``. If
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*initsigs* is ``0``, it skips initialization registration of signal handlers, which
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might be useful when Python is embedded.
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Use the :c:func:`Py_InitializeFromConfig` function to customize the
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:ref:`Python Initialization Configuration <init-config>`.
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.. c:function:: int Py_IsInitialized()
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Return true (nonzero) when the Python interpreter has been initialized, false
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(zero) if not. After :c:func:`Py_FinalizeEx` is called, this returns false until
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:c:func:`Py_Initialize` is called again.
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.. c:function:: int Py_IsFinalizing()
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Return true (non-zero) if the main Python interpreter is
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:term:`shutting down <interpreter shutdown>`. Return false (zero) otherwise.
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.. versionadded:: 3.13
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.. c:function:: int Py_FinalizeEx()
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Undo all initializations made by :c:func:`Py_Initialize` and subsequent use of
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Python/C API functions, and destroy all sub-interpreters (see
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:c:func:`Py_NewInterpreter` below) that were created and not yet destroyed since
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the last call to :c:func:`Py_Initialize`. Ideally, this frees all memory
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allocated by the Python interpreter. This is a no-op when called for a second
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time (without calling :c:func:`Py_Initialize` again first). Normally the
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return value is ``0``. If there were errors during finalization
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(flushing buffered data), ``-1`` is returned.
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This function is provided for a number of reasons. An embedding application
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might want to restart Python without having to restart the application itself.
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An application that has loaded the Python interpreter from a dynamically
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loadable library (or DLL) might want to free all memory allocated by Python
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before unloading the DLL. During a hunt for memory leaks in an application a
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developer might want to free all memory allocated by Python before exiting from
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the application.
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**Bugs and caveats:** The destruction of modules and objects in modules is done
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in random order; this may cause destructors (:meth:`~object.__del__` methods) to fail
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when they depend on other objects (even functions) or modules. Dynamically
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loaded extension modules loaded by Python are not unloaded. Small amounts of
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memory allocated by the Python interpreter may not be freed (if you find a leak,
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please report it). Memory tied up in circular references between objects is not
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freed. Some memory allocated by extension modules may not be freed. Some
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extensions may not work properly if their initialization routine is called more
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than once; this can happen if an application calls :c:func:`Py_Initialize` and
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:c:func:`Py_FinalizeEx` more than once.
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.. audit-event:: cpython._PySys_ClearAuditHooks "" c.Py_FinalizeEx
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.. versionadded:: 3.6
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.. c:function:: void Py_Finalize()
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This is a backwards-compatible version of :c:func:`Py_FinalizeEx` that
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disregards the return value.
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Process-wide parameters
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=======================
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.. c:function:: wchar_t* Py_GetProgramName()
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Return the program name set with :c:member:`PyConfig.program_name`, or the default.
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The returned string points into static storage; the caller should not modify its
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value.
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This function should not be called before :c:func:`Py_Initialize`, otherwise
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it returns ``NULL``.
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.. versionchanged:: 3.10
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It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
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.. deprecated-removed:: 3.13 3.15
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Get :data:`sys.executable` instead.
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.. c:function:: wchar_t* Py_GetPrefix()
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Return the *prefix* for installed platform-independent files. This is derived
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through a number of complicated rules from the program name set with
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:c:member:`PyConfig.program_name` and some environment variables; for example, if the
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program name is ``'/usr/local/bin/python'``, the prefix is ``'/usr/local'``. The
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returned string points into static storage; the caller should not modify its
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value. This corresponds to the :makevar:`prefix` variable in the top-level
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:file:`Makefile` and the :option:`--prefix` argument to the :program:`configure`
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script at build time. The value is available to Python code as ``sys.prefix``.
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It is only useful on Unix. See also the next function.
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This function should not be called before :c:func:`Py_Initialize`, otherwise
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it returns ``NULL``.
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.. versionchanged:: 3.10
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It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
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.. deprecated-removed:: 3.13 3.15
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Get :data:`sys.prefix` instead.
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.. c:function:: wchar_t* Py_GetExecPrefix()
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Return the *exec-prefix* for installed platform-*dependent* files. This is
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derived through a number of complicated rules from the program name set with
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:c:member:`PyConfig.program_name` and some environment variables; for example, if the
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program name is ``'/usr/local/bin/python'``, the exec-prefix is
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``'/usr/local'``. The returned string points into static storage; the caller
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should not modify its value. This corresponds to the :makevar:`exec_prefix`
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variable in the top-level :file:`Makefile` and the ``--exec-prefix``
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argument to the :program:`configure` script at build time. The value is
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available to Python code as ``sys.exec_prefix``. It is only useful on Unix.
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Background: The exec-prefix differs from the prefix when platform dependent
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files (such as executables and shared libraries) are installed in a different
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directory tree. In a typical installation, platform dependent files may be
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installed in the :file:`/usr/local/plat` subtree while platform independent may
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be installed in :file:`/usr/local`.
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Generally speaking, a platform is a combination of hardware and software
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families, e.g. Sparc machines running the Solaris 2.x operating system are
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considered the same platform, but Intel machines running Solaris 2.x are another
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platform, and Intel machines running Linux are yet another platform. Different
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major revisions of the same operating system generally also form different
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platforms. Non-Unix operating systems are a different story; the installation
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strategies on those systems are so different that the prefix and exec-prefix are
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meaningless, and set to the empty string. Note that compiled Python bytecode
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files are platform independent (but not independent from the Python version by
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which they were compiled!).
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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
|
|
Get :data:`sys.exec_prefix` instead.
|
|
|
|
|
|
.. 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
|
|
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
|
|
Get :data:`sys.path` instead.
|
|
|
|
|
|
.. c:function:: 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 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`.
|
|
|
|
See also the :c:var:`Py_Version` constant.
|
|
|
|
|
|
.. c:function:: 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 macOS, 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``.
|
|
|
|
|
|
.. c:function:: 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``.
|
|
|
|
|
|
.. c:function:: 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``.
|
|
|
|
|
|
.. c:function:: 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``.
|
|
|
|
|
|
.. 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
|
|
Get :c:member:`PyConfig.home` or :envvar:`PYTHONHOME` environment
|
|
variable instead.
|
|
|
|
|
|
.. _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 :term:`global
|
|
interpreter lock` or :term:`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: setswitchinterval() (in module sys)
|
|
|
|
Therefore, the rule exists that only the thread that has acquired the
|
|
:term:`GIL` may operate on Python objects or call Python/C API functions.
|
|
In order to emulate concurrency of execution, the interpreter regularly
|
|
tries to switch threads (see :func:`sys.setswitchinterval`). The lock is also
|
|
released around potentially blocking I/O operations like reading or writing
|
|
a file, so that other Python threads can run in the meantime.
|
|
|
|
.. index::
|
|
single: PyThreadState
|
|
single: PyThreadState
|
|
|
|
The Python interpreter keeps some thread-specific bookkeeping information
|
|
inside a data structure called :c:type:`PyThreadState`. There's also one
|
|
global variable pointing to the current :c:type:`PyThreadState`: it can
|
|
be retrieved using :c:func:`PyThreadState_Get`.
|
|
|
|
Releasing the GIL from extension code
|
|
-------------------------------------
|
|
|
|
Most extension code manipulating the :term:`GIL` 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 :c:macro:`Py_BEGIN_ALLOW_THREADS` macro opens a new block and declares a
|
|
hidden local variable; the :c:macro:`Py_END_ALLOW_THREADS` macro closes the
|
|
block.
|
|
|
|
The block above expands to the following code::
|
|
|
|
PyThreadState *_save;
|
|
|
|
_save = PyEval_SaveThread();
|
|
... Do some blocking I/O operation ...
|
|
PyEval_RestoreThread(_save);
|
|
|
|
.. index::
|
|
single: PyEval_RestoreThread()
|
|
single: PyEval_SaveThread()
|
|
|
|
Here is how these functions work: the global interpreter lock is used to protect the pointer to the
|
|
current thread state. When releasing the lock and saving the thread state,
|
|
the current thread state pointer must be retrieved before the lock is released
|
|
(since another thread could immediately acquire the lock and store its own thread
|
|
state in the global variable). Conversely, when acquiring the lock and restoring
|
|
the thread state, the lock must be acquired before storing the thread state
|
|
pointer.
|
|
|
|
.. note::
|
|
Calling system I/O functions is the most common use case for releasing
|
|
the GIL, but it can also be useful before calling long-running computations
|
|
which don't need access to Python objects, such as compression or
|
|
cryptographic functions operating over memory buffers. For example, the
|
|
standard :mod:`zlib` and :mod:`hashlib` modules release the GIL when
|
|
compressing or hashing data.
|
|
|
|
|
|
.. _gilstate:
|
|
|
|
Non-Python created threads
|
|
--------------------------
|
|
|
|
When threads are created using the dedicated Python APIs (such as the
|
|
:mod:`threading` module), a thread state is automatically associated to them
|
|
and the code showed above is therefore correct. However, when threads are
|
|
created from C (for example by a third-party library with its own thread
|
|
management), they don't hold the GIL, nor is there a thread state structure
|
|
for them.
|
|
|
|
If you need to call Python code from these threads (often this will be part
|
|
of a callback API provided by the aforementioned third-party library),
|
|
you must first register these threads with the interpreter by
|
|
creating a thread state data structure, then acquiring the GIL, and finally
|
|
storing their thread state pointer, before you can start using the Python/C
|
|
API. When you are done, you should reset the thread state pointer, release
|
|
the GIL, and finally free the thread state data structure.
|
|
|
|
The :c:func:`PyGILState_Ensure` and :c:func:`PyGILState_Release` functions do
|
|
all of the above automatically. The typical idiom for calling into Python
|
|
from a C thread is::
|
|
|
|
PyGILState_STATE gstate;
|
|
gstate = PyGILState_Ensure();
|
|
|
|
/* Perform Python actions here. */
|
|
result = CallSomeFunction();
|
|
/* evaluate result or handle exception */
|
|
|
|
/* Release the thread. No Python API allowed beyond this point. */
|
|
PyGILState_Release(gstate);
|
|
|
|
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.
|
|
|
|
|
|
.. _fork-and-threads:
|
|
|
|
Cautions about fork()
|
|
---------------------
|
|
|
|
Another important thing to note about threads is their behaviour in the face
|
|
of the C :c:func:`fork` call. On most systems with :c:func:`fork`, after a
|
|
process forks only the thread that issued the fork will exist. This has a
|
|
concrete impact both on how locks must be handled and on all stored state
|
|
in CPython's runtime.
|
|
|
|
The fact that only the "current" thread remains
|
|
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
|
|
:c:func:`!pthread_atfork` would need to be used to accomplish the same thing.
|
|
Additionally, when extending or embedding Python, calling :c:func:`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.
|
|
:c:func:`PyOS_AfterFork_Child` tries to reset the necessary locks, but is not
|
|
always able to.
|
|
|
|
The fact that all other threads go away also means that CPython's
|
|
runtime state there must be cleaned up properly, which :func:`os.fork`
|
|
does. This means finalizing all other :c:type:`PyThreadState` objects
|
|
belonging to the current interpreter and all other
|
|
:c:type:`PyInterpreterState` objects. Due to this and the special
|
|
nature of the :ref:`"main" interpreter <sub-interpreter-support>`,
|
|
:c:func:`fork` should only be called in that interpreter's "main"
|
|
thread, where the CPython global runtime was originally initialized.
|
|
The only exception is if :c:func:`exec` will be called immediately
|
|
after.
|
|
|
|
|
|
High-level API
|
|
--------------
|
|
|
|
These are the most commonly used types and functions when writing C extension
|
|
code, or when embedding the Python interpreter:
|
|
|
|
.. c:type:: 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.
|
|
|
|
|
|
.. c:type:: PyThreadState
|
|
|
|
This data structure represents the state of a single thread. The only public
|
|
data member is:
|
|
|
|
.. c:member:: PyInterpreterState *interp
|
|
|
|
This thread's interpreter state.
|
|
|
|
|
|
.. c:function:: PyThreadState* PyEval_SaveThread()
|
|
|
|
Release the global interpreter lock (if it has been created) 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.
|
|
|
|
|
|
.. c:function:: void PyEval_RestoreThread(PyThreadState *tstate)
|
|
|
|
Acquire the global interpreter lock (if it has been created) 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.
|
|
|
|
.. note::
|
|
Calling this function from a thread when the runtime is finalizing
|
|
will terminate the thread, even if the thread was not created by Python.
|
|
You can use :c:func:`Py_IsFinalizing` or :func:`sys.is_finalizing` to
|
|
check if the interpreter is in process of being finalized before calling
|
|
this function to avoid unwanted termination.
|
|
|
|
.. c:function:: 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``).
|
|
|
|
See also :c:func:`PyThreadState_GetUnchecked`.
|
|
|
|
|
|
.. c:function:: PyThreadState* PyThreadState_GetUnchecked()
|
|
|
|
Similar to :c:func:`PyThreadState_Get`, but don't kill the process with a
|
|
fatal error if it is NULL. The caller is responsible to check if the result
|
|
is NULL.
|
|
|
|
.. versionadded:: 3.13
|
|
In Python 3.5 to 3.12, the function was private and known as
|
|
``_PyThreadState_UncheckedGet()``.
|
|
|
|
|
|
.. c:function:: 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
|
|
and is not released.
|
|
|
|
|
|
The following functions use thread-local storage, and are not compatible
|
|
with sub-interpreters:
|
|
|
|
.. c:function:: 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 :c:func:`PyGILState_Release`. In general, other
|
|
thread-related APIs may be used between :c:func:`PyGILState_Ensure` and
|
|
:c:func:`PyGILState_Release` calls as long as the thread state is restored to
|
|
its previous state before the Release(). For example, normal usage of the
|
|
:c:macro:`Py_BEGIN_ALLOW_THREADS` and :c:macro:`Py_END_ALLOW_THREADS` macros is
|
|
acceptable.
|
|
|
|
The return value is an opaque "handle" to the thread state when
|
|
:c:func:`PyGILState_Ensure` was called, and must be passed to
|
|
:c:func:`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 :c:func:`PyGILState_Ensure` must save the handle for its call
|
|
to :c:func:`PyGILState_Release`.
|
|
|
|
When the function returns, the current thread will hold the GIL and 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 terminate the thread, even if the thread was not created by Python.
|
|
You can use :c:func:`Py_IsFinalizing` or :func:`sys.is_finalizing` to
|
|
check if the interpreter is in process of being finalized before calling
|
|
this function to avoid unwanted termination.
|
|
|
|
.. c:function:: 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 :c:func:`PyGILState_Ensure` call
|
|
(but generally this state will be unknown to the caller, hence the use of the
|
|
GILState API).
|
|
|
|
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 current thread state for this thread. May return ``NULL`` if no
|
|
GILState API has been used on the current thread. Note that the main thread
|
|
always has such a thread-state, even if no auto-thread-state call has been
|
|
made on the main thread. This is mainly a helper/diagnostic function.
|
|
|
|
|
|
.. c:function:: int PyGILState_Check()
|
|
|
|
Return ``1`` if the current thread is holding the 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 GIL 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 GIL is locked can allow the caller to perform sensitive
|
|
actions or otherwise behave differently.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
The following macros are normally used without a trailing semicolon; look for
|
|
example usage in the Python source distribution.
|
|
|
|
|
|
.. c:macro:: 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
|
|
:c:macro:`Py_END_ALLOW_THREADS` macro. See above for further discussion of this
|
|
macro.
|
|
|
|
|
|
.. c:macro:: 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
|
|
:c:macro:`Py_BEGIN_ALLOW_THREADS` macro. See above for further discussion of
|
|
this macro.
|
|
|
|
|
|
.. c:macro:: Py_BLOCK_THREADS
|
|
|
|
This macro expands to ``PyEval_RestoreThread(_save);``: it is equivalent to
|
|
:c:macro:`Py_END_ALLOW_THREADS` without the closing brace.
|
|
|
|
|
|
.. c:macro:: Py_UNBLOCK_THREADS
|
|
|
|
This macro expands to ``_save = PyEval_SaveThread();``: it is equivalent to
|
|
:c:macro:`Py_BEGIN_ALLOW_THREADS` without the opening brace and variable
|
|
declaration.
|
|
|
|
|
|
Low-level API
|
|
-------------
|
|
|
|
All of the following functions must be called after :c:func:`Py_Initialize`.
|
|
|
|
.. versionchanged:: 3.7
|
|
:c:func:`Py_Initialize()` now initializes the :term:`GIL`.
|
|
|
|
|
|
.. c:function:: 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.
|
|
|
|
.. audit-event:: cpython.PyInterpreterState_New "" c.PyInterpreterState_New
|
|
|
|
|
|
.. c:function:: void PyInterpreterState_Clear(PyInterpreterState *interp)
|
|
|
|
Reset all information in an interpreter state object. The global interpreter
|
|
lock must be held.
|
|
|
|
.. audit-event:: cpython.PyInterpreterState_Clear "" c.PyInterpreterState_Clear
|
|
|
|
|
|
.. c:function:: 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
|
|
:c:func:`PyInterpreterState_Clear`.
|
|
|
|
|
|
.. c:function:: 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.
|
|
|
|
|
|
.. c:function:: void PyThreadState_Clear(PyThreadState *tstate)
|
|
|
|
Reset all information in a thread state object. The global interpreter lock
|
|
must be held.
|
|
|
|
.. versionchanged:: 3.9
|
|
This function now calls the :c:member:`PyThreadState.on_delete` callback.
|
|
Previously, that happened in :c:func:`PyThreadState_Delete`.
|
|
|
|
|
|
.. c:function:: 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
|
|
:c:func:`PyThreadState_Clear`.
|
|
|
|
|
|
.. c:function:: void PyThreadState_DeleteCurrent(void)
|
|
|
|
Destroy the current thread state and release the global interpreter lock.
|
|
Like :c:func:`PyThreadState_Delete`, the global interpreter lock need not
|
|
be held. The thread state must have been reset with a previous call
|
|
to :c:func:`PyThreadState_Clear`.
|
|
|
|
|
|
.. c:function:: PyFrameObject* PyThreadState_GetFrame(PyThreadState *tstate)
|
|
|
|
Get the current frame of the Python thread state *tstate*.
|
|
|
|
Return a :term:`strong reference`. Return ``NULL`` if no frame is currently
|
|
executing.
|
|
|
|
See also :c:func:`PyEval_GetFrame`.
|
|
|
|
*tstate* must not be ``NULL``.
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
|
|
.. c:function:: uint64_t PyThreadState_GetID(PyThreadState *tstate)
|
|
|
|
Get the unique thread state identifier of the Python thread state *tstate*.
|
|
|
|
*tstate* must not be ``NULL``.
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
|
|
.. c:function:: PyInterpreterState* PyThreadState_GetInterpreter(PyThreadState *tstate)
|
|
|
|
Get the interpreter of the Python thread state *tstate*.
|
|
|
|
*tstate* must not be ``NULL``.
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
|
|
.. c:function:: void PyThreadState_EnterTracing(PyThreadState *tstate)
|
|
|
|
Suspend tracing and profiling in the Python thread state *tstate*.
|
|
|
|
Resume them using the :c:func:`PyThreadState_LeaveTracing` function.
|
|
|
|
.. versionadded:: 3.11
|
|
|
|
|
|
.. c:function:: void PyThreadState_LeaveTracing(PyThreadState *tstate)
|
|
|
|
Resume tracing and profiling in the Python thread state *tstate* suspended
|
|
by the :c:func:`PyThreadState_EnterTracing` function.
|
|
|
|
See also :c:func:`PyEval_SetTrace` and :c:func:`PyEval_SetProfile`
|
|
functions.
|
|
|
|
.. versionadded:: 3.11
|
|
|
|
|
|
.. c:function:: PyInterpreterState* PyInterpreterState_Get(void)
|
|
|
|
Get the current interpreter.
|
|
|
|
Issue a fatal error if there no current Python thread state or no current
|
|
interpreter. It cannot return NULL.
|
|
|
|
The caller must hold the GIL.
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
|
|
.. c:function:: int64_t PyInterpreterState_GetID(PyInterpreterState *interp)
|
|
|
|
Return the interpreter's unique ID. If there was any error in doing
|
|
so then ``-1`` is returned and an error is set.
|
|
|
|
The caller must hold the GIL.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
|
|
.. c:function:: PyObject* PyInterpreterState_GetDict(PyInterpreterState *interp)
|
|
|
|
Return a dictionary in which interpreter-specific data may be stored.
|
|
If this function returns ``NULL`` then no exception has been raised and
|
|
the caller should assume no interpreter-specific dict is available.
|
|
|
|
This is not a replacement for :c:func:`PyModule_GetState()`, which
|
|
extensions should use to store interpreter-specific state information.
|
|
|
|
.. versionadded:: 3.8
|
|
|
|
.. c:type:: PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, _PyInterpreterFrame *frame, int throwflag)
|
|
|
|
Type of a frame evaluation function.
|
|
|
|
The *throwflag* parameter is used by the ``throw()`` method of generators:
|
|
if non-zero, handle the current exception.
|
|
|
|
.. versionchanged:: 3.9
|
|
The function now takes a *tstate* parameter.
|
|
|
|
.. versionchanged:: 3.11
|
|
The *frame* parameter changed from ``PyFrameObject*`` to ``_PyInterpreterFrame*``.
|
|
|
|
.. c:function:: _PyFrameEvalFunction _PyInterpreterState_GetEvalFrameFunc(PyInterpreterState *interp)
|
|
|
|
Get the frame evaluation function.
|
|
|
|
See the :pep:`523` "Adding a frame evaluation API to CPython".
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
.. c:function:: void _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState *interp, _PyFrameEvalFunction eval_frame)
|
|
|
|
Set the frame evaluation function.
|
|
|
|
See the :pep:`523` "Adding a frame evaluation API to CPython".
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
|
|
.. c:function:: 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.
|
|
|
|
|
|
.. c:function:: int PyThreadState_SetAsyncExc(unsigned 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 ``NULL``, the pending
|
|
exception (if any) for the thread is cleared. This raises no exceptions.
|
|
|
|
.. versionchanged:: 3.7
|
|
The type of the *id* parameter changed from :c:expr:`long` to
|
|
:c:expr:`unsigned long`.
|
|
|
|
.. c:function:: void PyEval_AcquireThread(PyThreadState *tstate)
|
|
|
|
Acquire the global interpreter lock and set the current thread state to
|
|
*tstate*, which must not be ``NULL``. The lock must have been created earlier.
|
|
If this thread already has the lock, deadlock ensues.
|
|
|
|
.. note::
|
|
Calling this function from a thread when the runtime is finalizing
|
|
will terminate the thread, even if the thread was not created by Python.
|
|
You can use :c:func:`Py_IsFinalizing` or :func:`sys.is_finalizing` to
|
|
check if the interpreter is in process of being finalized before calling
|
|
this function to avoid unwanted termination.
|
|
|
|
.. versionchanged:: 3.8
|
|
Updated to be consistent with :c:func:`PyEval_RestoreThread`,
|
|
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`,
|
|
and terminate the current thread if called while the interpreter is finalizing.
|
|
|
|
:c:func:`PyEval_RestoreThread` is a higher-level function which is always
|
|
available (even when threads have not been initialized).
|
|
|
|
|
|
.. c:function:: 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.
|
|
|
|
:c:func:`PyEval_SaveThread` is a higher-level function which is always
|
|
available (even when threads have not been initialized).
|
|
|
|
|
|
.. _sub-interpreter-support:
|
|
|
|
Sub-interpreter support
|
|
=======================
|
|
|
|
While in most uses, you will only embed a single Python interpreter, there
|
|
are cases where you need to create several independent interpreters in the
|
|
same process and perhaps even in the same thread. Sub-interpreters allow
|
|
you to do that.
|
|
|
|
The "main" interpreter is the first one created when the runtime initializes.
|
|
It is usually the only Python interpreter in a process. Unlike sub-interpreters,
|
|
the main interpreter has unique process-global responsibilities like signal
|
|
handling. It is also responsible for execution during runtime initialization and
|
|
is usually the active interpreter during runtime finalization. The
|
|
:c:func:`PyInterpreterState_Main` function returns a pointer to its state.
|
|
|
|
You can switch between sub-interpreters using the :c:func:`PyThreadState_Swap`
|
|
function. You can create and destroy them using the following functions:
|
|
|
|
|
|
.. c:type:: PyInterpreterConfig
|
|
|
|
Structure containing most parameters to configure a sub-interpreter.
|
|
Its values are used only in :c:func:`Py_NewInterpreterFromConfig` and
|
|
never modified by the runtime.
|
|
|
|
.. versionadded:: 3.12
|
|
|
|
Structure fields:
|
|
|
|
.. c:member:: int use_main_obmalloc
|
|
|
|
If this is ``0`` then the sub-interpreter will use its own
|
|
"object" allocator state.
|
|
Otherwise it will use (share) the main interpreter's.
|
|
|
|
If this is ``0`` then
|
|
:c:member:`~PyInterpreterConfig.check_multi_interp_extensions`
|
|
must be ``1`` (non-zero).
|
|
If this is ``1`` then :c:member:`~PyInterpreterConfig.gil`
|
|
must not be :c:macro:`PyInterpreterConfig_OWN_GIL`.
|
|
|
|
.. c:member:: int allow_fork
|
|
|
|
If this is ``0`` then the runtime will not support forking the
|
|
process in any thread where the sub-interpreter is currently active.
|
|
Otherwise fork is unrestricted.
|
|
|
|
Note that the :mod:`subprocess` module still works
|
|
when fork is disallowed.
|
|
|
|
.. c:member:: int allow_exec
|
|
|
|
If this is ``0`` then the runtime will not support replacing the
|
|
current process via exec (e.g. :func:`os.execv`) in any thread
|
|
where the sub-interpreter is currently active.
|
|
Otherwise exec is unrestricted.
|
|
|
|
Note that the :mod:`subprocess` module still works
|
|
when exec is disallowed.
|
|
|
|
.. c:member:: int allow_threads
|
|
|
|
If this is ``0`` then the sub-interpreter's :mod:`threading` module
|
|
won't create threads.
|
|
Otherwise threads are allowed.
|
|
|
|
.. c:member:: int allow_daemon_threads
|
|
|
|
If this is ``0`` then the sub-interpreter's :mod:`threading` module
|
|
won't create daemon threads.
|
|
Otherwise daemon threads are allowed (as long as
|
|
:c:member:`~PyInterpreterConfig.allow_threads` is non-zero).
|
|
|
|
.. c:member:: int check_multi_interp_extensions
|
|
|
|
If this is ``0`` then all extension modules may be imported,
|
|
including legacy (single-phase init) modules,
|
|
in any thread where the sub-interpreter is currently active.
|
|
Otherwise only multi-phase init extension modules
|
|
(see :pep:`489`) may be imported.
|
|
(Also see :c:macro:`Py_mod_multiple_interpreters`.)
|
|
|
|
This must be ``1`` (non-zero) if
|
|
:c:member:`~PyInterpreterConfig.use_main_obmalloc` is ``0``.
|
|
|
|
.. c:member:: int gil
|
|
|
|
This determines the operation of the GIL for the sub-interpreter.
|
|
It may be one of the following:
|
|
|
|
.. c:namespace:: NULL
|
|
|
|
.. c:macro:: PyInterpreterConfig_DEFAULT_GIL
|
|
|
|
Use the default selection (:c:macro:`PyInterpreterConfig_SHARED_GIL`).
|
|
|
|
.. c:macro:: PyInterpreterConfig_SHARED_GIL
|
|
|
|
Use (share) the main interpreter's GIL.
|
|
|
|
.. c:macro:: PyInterpreterConfig_OWN_GIL
|
|
|
|
Use the sub-interpreter's own GIL.
|
|
|
|
If this is :c:macro:`PyInterpreterConfig_OWN_GIL` then
|
|
:c:member:`PyInterpreterConfig.use_main_obmalloc` must be ``0``.
|
|
|
|
|
|
.. c:function:: PyStatus Py_NewInterpreterFromConfig(PyThreadState **tstate_p, const PyInterpreterConfig *config)
|
|
|
|
.. index::
|
|
pair: module; builtins
|
|
pair: module; __main__
|
|
pair: 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
|
|
file descriptors).
|
|
|
|
The given *config* controls the options with which the interpreter
|
|
is initialized.
|
|
|
|
Upon success, *tstate_p* will be set 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,
|
|
*tstate_p* is set to ``NULL``;
|
|
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. Likewise a current thread state must be set on entry. On
|
|
success, the returned thread state will be set as current. If the
|
|
sub-interpreter is created with its own GIL then the GIL of the
|
|
calling interpreter will be released. When the function returns,
|
|
the new interpreter's GIL will be held by the current thread and
|
|
the previously interpreter's GIL will remain released here.
|
|
|
|
.. versionadded:: 3.12
|
|
|
|
Sub-interpreters are most effective when isolated from each other,
|
|
with certain functionality restricted::
|
|
|
|
PyInterpreterConfig config = {
|
|
.use_main_obmalloc = 0,
|
|
.allow_fork = 0,
|
|
.allow_exec = 0,
|
|
.allow_threads = 1,
|
|
.allow_daemon_threads = 0,
|
|
.check_multi_interp_extensions = 1,
|
|
.gil = PyInterpreterConfig_OWN_GIL,
|
|
};
|
|
PyThreadState *tstate = Py_NewInterpreterFromConfig(&config);
|
|
|
|
Note that the config is used only briefly and does not get modified.
|
|
During initialization the config's values are converted into various
|
|
:c:type:`PyInterpreterState` values. A read-only copy of the config
|
|
may be stored internally on the :c:type:`PyInterpreterState`.
|
|
|
|
.. index::
|
|
single: Py_FinalizeEx()
|
|
single: Py_Initialize()
|
|
|
|
Extension modules are shared between (sub-)interpreters as follows:
|
|
|
|
* For modules using multi-phase initialization,
|
|
e.g. :c:func:`PyModule_FromDefAndSpec`, a separate module object is
|
|
created and initialized for each interpreter.
|
|
Only C-level static and global variables are shared between these
|
|
module objects.
|
|
|
|
* For modules using single-phase initialization,
|
|
e.g. :c:func:`PyModule_Create`, 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.
|
|
Objects in the module's dictionary thus end up shared across
|
|
(sub-)interpreters, which might cause unwanted behavior (see
|
|
`Bugs and caveats`_ below).
|
|
|
|
Note that this is different from what happens when an extension is
|
|
imported after the interpreter has been completely re-initialized by
|
|
calling :c:func:`Py_FinalizeEx` and :c:func:`Py_Initialize`; in that
|
|
case, the extension's ``initmodule`` function *is* called again.
|
|
As with multi-phase initialization, this means that only C-level static
|
|
and global variables are shared between these modules.
|
|
|
|
.. index:: single: close() (in module os)
|
|
|
|
|
|
.. c:function:: PyThreadState* Py_NewInterpreter(void)
|
|
|
|
.. index::
|
|
pair: module; builtins
|
|
pair: module; __main__
|
|
pair: module; sys
|
|
single: stdout (in module sys)
|
|
single: stderr (in module sys)
|
|
single: stdin (in module sys)
|
|
|
|
Create a new sub-interpreter. This is essentially just a wrapper
|
|
around :c:func:`Py_NewInterpreterFromConfig` with a config that
|
|
preserves the existing behavior. The result is an unisolated
|
|
sub-interpreter that shares the main interpreter's GIL, allows
|
|
fork/exec, allows daemon threads, and allows single-phase init
|
|
modules.
|
|
|
|
|
|
.. c:function:: void Py_EndInterpreter(PyThreadState *tstate)
|
|
|
|
.. index:: single: Py_FinalizeEx()
|
|
|
|
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
|
|
used by the target interpreter must be held before calling this
|
|
function. No GIL is held when it returns.
|
|
|
|
:c:func:`Py_FinalizeEx` will destroy all sub-interpreters that
|
|
haven't been explicitly destroyed at that point.
|
|
|
|
|
|
A Per-Interpreter GIL
|
|
---------------------
|
|
|
|
Using :c:func:`Py_NewInterpreterFromConfig` you can create
|
|
a sub-interpreter that is completely isolated from other interpreters,
|
|
including having its own GIL. The most important benefit of this
|
|
isolation is that such an interpreter can execute Python code without
|
|
being blocked by other interpreters or blocking any others. Thus a
|
|
single Python process can truly take advantage of multiple CPU cores
|
|
when running Python code. The isolation also encourages a different
|
|
approach to concurrency than that of just using threads.
|
|
(See :pep:`554`.)
|
|
|
|
Using an isolated interpreter requires vigilance in preserving that
|
|
isolation. That especially means not sharing any objects or mutable
|
|
state without guarantees about thread-safety. Even objects that are
|
|
otherwise immutable (e.g. ``None``, ``(1, 5)``) can't normally be shared
|
|
because of the refcount. One simple but less-efficient approach around
|
|
this is to use a global lock around all use of some state (or object).
|
|
Alternately, effectively immutable objects (like integers or strings)
|
|
can be made safe in spite of their refcounts by making them :term:`immortal`.
|
|
In fact, this has been done for the builtin singletons, small integers,
|
|
and a number of other builtin objects.
|
|
|
|
If you preserve isolation then you will have access to proper multi-core
|
|
computing without the complications that come with free-threading.
|
|
Failure to preserve isolation will expose you to the full consequences
|
|
of free-threading, including races and hard-to-debug crashes.
|
|
|
|
Aside from that, one of the main challenges of using multiple isolated
|
|
interpreters is how to communicate between them safely (not break
|
|
isolation) and efficiently. The runtime and stdlib do not provide
|
|
any standard approach to this yet. A future stdlib module would help
|
|
mitigate the effort of preserving isolation and expose effective tools
|
|
for communicating (and sharing) data between interpreters.
|
|
|
|
.. versionadded:: 3.12
|
|
|
|
|
|
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 using single-phase initialization
|
|
or (static) global variables.
|
|
It is possible to insert objects created in one sub-interpreter into
|
|
a namespace of another (sub-)interpreter; this should be avoided if possible.
|
|
|
|
Special care should be taken 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. It is equally important to avoid sharing
|
|
objects from which the above are reachable.
|
|
|
|
Also note that combining this functionality with ``PyGILState_*`` APIs
|
|
is delicate, because these APIs assume a bijection between Python thread states
|
|
and OS-level threads, an assumption broken by the presence of sub-interpreters.
|
|
It is highly recommended that you don't switch sub-interpreters between a pair
|
|
of matching :c:func:`PyGILState_Ensure` and :c:func:`PyGILState_Release` calls.
|
|
Furthermore, extensions (such as :mod:`ctypes`) using these APIs to allow calling
|
|
of Python code from non-Python created threads will probably be broken when using
|
|
sub-interpreters.
|
|
|
|
|
|
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 pointer argument.
|
|
|
|
|
|
.. c:function:: int Py_AddPendingCall(int (*func)(void *), void *arg)
|
|
|
|
.. index:: single: Py_AddPendingCall()
|
|
|
|
Schedule a function to be called from the main interpreter thread. On
|
|
success, ``0`` is returned and *func* is queued for being called in the
|
|
main thread. On failure, ``-1`` is returned without setting any exception.
|
|
|
|
When successfully queued, *func* will be *eventually* called from the
|
|
main interpreter thread with the argument *arg*. It will be called
|
|
asynchronously with respect to normally running Python code, but with
|
|
both these conditions met:
|
|
|
|
* on a :term:`bytecode` boundary;
|
|
* with the main thread holding the :term:`global interpreter lock`
|
|
(*func* can therefore use the full C API).
|
|
|
|
*func* must return ``0`` on success, or ``-1`` on failure with an exception
|
|
set. *func* won't be interrupted to perform another asynchronous
|
|
notification recursively, but it can still be interrupted to switch
|
|
threads if the global interpreter lock is released.
|
|
|
|
This function doesn't need a current thread state to run, and it doesn't
|
|
need the global interpreter lock.
|
|
|
|
To call this function in a subinterpreter, the caller must hold the GIL.
|
|
Otherwise, the function *func* can be scheduled to be called from the wrong
|
|
interpreter.
|
|
|
|
.. warning::
|
|
This is a low-level function, only useful for very special cases.
|
|
There is no guarantee that *func* will be called as quick as
|
|
possible. If the main thread is busy executing a system call,
|
|
*func* won't be called before the system call returns. This
|
|
function is generally **not** suitable for calling Python code from
|
|
arbitrary C threads. Instead, use the :ref:`PyGILState API<gilstate>`.
|
|
|
|
.. versionchanged:: 3.9
|
|
If this function is called in a subinterpreter, the function *func* is
|
|
now scheduled to be called from the subinterpreter, rather than being
|
|
called from the main interpreter. Each subinterpreter now has its own
|
|
list of scheduled calls.
|
|
|
|
.. 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.
|
|
|
|
|
|
.. c:type:: int (*Py_tracefunc)(PyObject *obj, PyFrameObject *frame, int what, PyObject *arg)
|
|
|
|
The type of the trace function registered using :c:func:`PyEval_SetProfile` and
|
|
:c:func:`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 :c:data:`PyTrace_CALL`,
|
|
:c:data:`PyTrace_EXCEPTION`, :c:data:`PyTrace_LINE`, :c:data:`PyTrace_RETURN`,
|
|
:c:data:`PyTrace_C_CALL`, :c:data:`PyTrace_C_EXCEPTION`, :c:data:`PyTrace_C_RETURN`,
|
|
or :c:data:`PyTrace_OPCODE`, and *arg* depends on the value of *what*:
|
|
|
|
+-------------------------------+----------------------------------------+
|
|
| Value of *what* | Meaning of *arg* |
|
|
+===============================+========================================+
|
|
| :c:data:`PyTrace_CALL` | Always :c:data:`Py_None`. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_EXCEPTION` | Exception information as returned by |
|
|
| | :func:`sys.exc_info`. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_LINE` | Always :c:data:`Py_None`. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_RETURN` | Value being returned to the caller, |
|
|
| | or ``NULL`` if caused by an exception. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_C_CALL` | Function object being called. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_C_EXCEPTION` | Function object being called. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_C_RETURN` | Function object being called. |
|
|
+-------------------------------+----------------------------------------+
|
|
| :c:data:`PyTrace_OPCODE` | Always :c:data:`Py_None`. |
|
|
+-------------------------------+----------------------------------------+
|
|
|
|
.. c:var:: int PyTrace_CALL
|
|
|
|
The value of the *what* parameter to a :c:type:`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.
|
|
|
|
|
|
.. c:var:: int PyTrace_EXCEPTION
|
|
|
|
The value of the *what* parameter to a :c:type:`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.
|
|
|
|
|
|
.. c:var:: int PyTrace_LINE
|
|
|
|
The value passed as the *what* parameter to a :c:type:`Py_tracefunc` function
|
|
(but not a profiling function) when a line-number event is being reported.
|
|
It may be disabled for a frame by setting :attr:`f_trace_lines` to *0* on that frame.
|
|
|
|
|
|
.. c:var:: int PyTrace_RETURN
|
|
|
|
The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a
|
|
call is about to return.
|
|
|
|
|
|
.. c:var:: int PyTrace_C_CALL
|
|
|
|
The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a C
|
|
function is about to be called.
|
|
|
|
|
|
.. c:var:: int PyTrace_C_EXCEPTION
|
|
|
|
The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a C
|
|
function has raised an exception.
|
|
|
|
|
|
.. c:var:: int PyTrace_C_RETURN
|
|
|
|
The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a C
|
|
function has returned.
|
|
|
|
|
|
.. c:var:: int PyTrace_OPCODE
|
|
|
|
The value for the *what* parameter to :c:type:`Py_tracefunc` functions (but not
|
|
profiling functions) when a new opcode is about to be executed. This event is
|
|
not emitted by default: it must be explicitly requested by setting
|
|
:attr:`f_trace_opcodes` to *1* on the frame.
|
|
|
|
|
|
.. c:function:: 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 :c:data:`PyTrace_LINE`
|
|
:c:data:`PyTrace_OPCODE` and :c:data:`PyTrace_EXCEPTION`.
|
|
|
|
See also the :func:`sys.setprofile` function.
|
|
|
|
The caller must hold the :term:`GIL`.
|
|
|
|
.. c:function:: void PyEval_SetProfileAllThreads(Py_tracefunc func, PyObject *obj)
|
|
|
|
Like :c:func:`PyEval_SetProfile` but sets the profile function in all running threads
|
|
belonging to the current interpreter instead of the setting it only on the current thread.
|
|
|
|
The caller must hold the :term:`GIL`.
|
|
|
|
As :c:func:`PyEval_SetProfile`, this function ignores any exceptions raised while
|
|
setting the profile functions in all threads.
|
|
|
|
.. versionadded:: 3.12
|
|
|
|
|
|
.. c:function:: void PyEval_SetTrace(Py_tracefunc func, PyObject *obj)
|
|
|
|
Set the tracing function to *func*. This is similar to
|
|
:c:func:`PyEval_SetProfile`, except the tracing function does receive line-number
|
|
events and per-opcode events, but does not receive any event related to C function
|
|
objects being called. Any trace function registered using :c:func:`PyEval_SetTrace`
|
|
will not receive :c:data:`PyTrace_C_CALL`, :c:data:`PyTrace_C_EXCEPTION` or
|
|
:c:data:`PyTrace_C_RETURN` as a value for the *what* parameter.
|
|
|
|
See also the :func:`sys.settrace` function.
|
|
|
|
The caller must hold the :term:`GIL`.
|
|
|
|
.. c:function:: void PyEval_SetTraceAllThreads(Py_tracefunc func, PyObject *obj)
|
|
|
|
Like :c:func:`PyEval_SetTrace` but sets the tracing function in all running threads
|
|
belonging to the current interpreter instead of the setting it only on the current thread.
|
|
|
|
The caller must hold the :term:`GIL`.
|
|
|
|
As :c:func:`PyEval_SetTrace`, this function ignores any exceptions raised while
|
|
setting the trace functions in all threads.
|
|
|
|
.. versionadded:: 3.12
|
|
|
|
|
|
.. _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.
|
|
|
|
|
|
.. c:function:: PyInterpreterState* PyInterpreterState_Head()
|
|
|
|
Return the interpreter state object at the head of the list of all such objects.
|
|
|
|
|
|
.. c:function:: PyInterpreterState* PyInterpreterState_Main()
|
|
|
|
Return the main interpreter state object.
|
|
|
|
|
|
.. c:function:: PyInterpreterState* PyInterpreterState_Next(PyInterpreterState *interp)
|
|
|
|
Return the next interpreter state object after *interp* from the list of all
|
|
such objects.
|
|
|
|
|
|
.. c:function:: PyThreadState * PyInterpreterState_ThreadHead(PyInterpreterState *interp)
|
|
|
|
Return the pointer to the first :c:type:`PyThreadState` object in the list of
|
|
threads associated with the interpreter *interp*.
|
|
|
|
|
|
.. c:function:: PyThreadState* PyThreadState_Next(PyThreadState *tstate)
|
|
|
|
Return the next thread state object after *tstate* from the list of all such
|
|
objects belonging to the same :c:type:`PyInterpreterState` object.
|
|
|
|
|
|
.. _thread-local-storage:
|
|
|
|
Thread Local Storage Support
|
|
============================
|
|
|
|
.. sectionauthor:: Masayuki Yamamoto <ma3yuki.8mamo10@gmail.com>
|
|
|
|
The Python interpreter provides low-level support for thread-local storage
|
|
(TLS) which wraps the underlying native TLS implementation to support the
|
|
Python-level thread local storage API (:class:`threading.local`). The
|
|
CPython C level APIs are similar to those offered by pthreads and Windows:
|
|
use a thread key and functions to associate a :c:expr:`void*` value per
|
|
thread.
|
|
|
|
The GIL does *not* need to be held when calling these functions; they supply
|
|
their own locking.
|
|
|
|
Note that :file:`Python.h` does not include the declaration of the TLS APIs,
|
|
you need to include :file:`pythread.h` to use thread-local storage.
|
|
|
|
.. note::
|
|
None of these API functions handle memory management on behalf of the
|
|
:c:expr:`void*` values. You need to allocate and deallocate them yourself.
|
|
If the :c:expr:`void*` values happen to be :c:expr:`PyObject*`, these
|
|
functions don't do refcount operations on them either.
|
|
|
|
.. _thread-specific-storage-api:
|
|
|
|
Thread Specific Storage (TSS) API
|
|
---------------------------------
|
|
|
|
TSS API is introduced to supersede the use of the existing TLS API within the
|
|
CPython interpreter. This API uses a new type :c:type:`Py_tss_t` instead of
|
|
:c:expr:`int` to represent thread keys.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. seealso:: "A New C-API for Thread-Local Storage in CPython" (:pep:`539`)
|
|
|
|
|
|
.. c:type:: Py_tss_t
|
|
|
|
This data structure represents the state of a thread key, the definition of
|
|
which may depend on the underlying TLS implementation, and it has an
|
|
internal field representing the key's initialization state. There are no
|
|
public members in this structure.
|
|
|
|
When :ref:`Py_LIMITED_API <stable>` is not defined, static allocation of
|
|
this type by :c:macro:`Py_tss_NEEDS_INIT` is allowed.
|
|
|
|
|
|
.. c:macro:: Py_tss_NEEDS_INIT
|
|
|
|
This macro expands to the initializer for :c:type:`Py_tss_t` variables.
|
|
Note that this macro won't be defined with :ref:`Py_LIMITED_API <stable>`.
|
|
|
|
|
|
Dynamic Allocation
|
|
~~~~~~~~~~~~~~~~~~
|
|
|
|
Dynamic allocation of the :c:type:`Py_tss_t`, required in extension modules
|
|
built with :ref:`Py_LIMITED_API <stable>`, where static allocation of this type
|
|
is not possible due to its implementation being opaque at build time.
|
|
|
|
|
|
.. c:function:: Py_tss_t* PyThread_tss_alloc()
|
|
|
|
Return a value which is the same state as a value initialized with
|
|
:c:macro:`Py_tss_NEEDS_INIT`, or ``NULL`` in the case of dynamic allocation
|
|
failure.
|
|
|
|
|
|
.. c:function:: void PyThread_tss_free(Py_tss_t *key)
|
|
|
|
Free the given *key* allocated by :c:func:`PyThread_tss_alloc`, after
|
|
first calling :c:func:`PyThread_tss_delete` to ensure any associated
|
|
thread locals have been unassigned. This is a no-op if the *key*
|
|
argument is ``NULL``.
|
|
|
|
.. note::
|
|
A freed key becomes a dangling pointer. You should reset the key to
|
|
``NULL``.
|
|
|
|
|
|
Methods
|
|
~~~~~~~
|
|
|
|
The parameter *key* of these functions must not be ``NULL``. Moreover, the
|
|
behaviors of :c:func:`PyThread_tss_set` and :c:func:`PyThread_tss_get` are
|
|
undefined if the given :c:type:`Py_tss_t` has not been initialized by
|
|
:c:func:`PyThread_tss_create`.
|
|
|
|
|
|
.. c:function:: int PyThread_tss_is_created(Py_tss_t *key)
|
|
|
|
Return a non-zero value if the given :c:type:`Py_tss_t` has been initialized
|
|
by :c:func:`PyThread_tss_create`.
|
|
|
|
|
|
.. c:function:: int PyThread_tss_create(Py_tss_t *key)
|
|
|
|
Return a zero value on successful initialization of a TSS key. The behavior
|
|
is undefined if the value pointed to by the *key* argument is not
|
|
initialized by :c:macro:`Py_tss_NEEDS_INIT`. This function can be called
|
|
repeatedly on the same key -- calling it on an already initialized key is a
|
|
no-op and immediately returns success.
|
|
|
|
|
|
.. c:function:: void PyThread_tss_delete(Py_tss_t *key)
|
|
|
|
Destroy a TSS key to forget the values associated with the key across all
|
|
threads, and change the key's initialization state to uninitialized. A
|
|
destroyed key is able to be initialized again by
|
|
:c:func:`PyThread_tss_create`. This function can be called repeatedly on
|
|
the same key -- calling it on an already destroyed key is a no-op.
|
|
|
|
|
|
.. c:function:: int PyThread_tss_set(Py_tss_t *key, void *value)
|
|
|
|
Return a zero value to indicate successfully associating a :c:expr:`void*`
|
|
value with a TSS key in the current thread. Each thread has a distinct
|
|
mapping of the key to a :c:expr:`void*` value.
|
|
|
|
|
|
.. c:function:: void* PyThread_tss_get(Py_tss_t *key)
|
|
|
|
Return the :c:expr:`void*` value associated with a TSS key in the current
|
|
thread. This returns ``NULL`` if no value is associated with the key in the
|
|
current thread.
|
|
|
|
|
|
.. _thread-local-storage-api:
|
|
|
|
Thread Local Storage (TLS) API
|
|
------------------------------
|
|
|
|
.. deprecated:: 3.7
|
|
This API is superseded by
|
|
:ref:`Thread Specific Storage (TSS) API <thread-specific-storage-api>`.
|
|
|
|
.. note::
|
|
This version of the API does not support platforms where the native TLS key
|
|
is defined in a way that cannot be safely cast to ``int``. On such platforms,
|
|
:c:func:`PyThread_create_key` will return immediately with a failure status,
|
|
and the other TLS functions will all be no-ops on such platforms.
|
|
|
|
Due to the compatibility problem noted above, this version of the API should not
|
|
be used in new code.
|
|
|
|
.. c:function:: int PyThread_create_key()
|
|
.. c:function:: void PyThread_delete_key(int key)
|
|
.. c:function:: int PyThread_set_key_value(int key, void *value)
|
|
.. c:function:: void* PyThread_get_key_value(int key)
|
|
.. c:function:: void PyThread_delete_key_value(int key)
|
|
.. c:function:: void PyThread_ReInitTLS()
|
|
|