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Diffstat (limited to 'Doc/library/threading.rst')
| -rw-r--r-- | Doc/library/threading.rst | 83 |
1 files changed, 41 insertions, 42 deletions
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst index 43087ef..eaba38b 100644 --- a/Doc/library/threading.rst +++ b/Doc/library/threading.rst @@ -20,17 +20,6 @@ The :mod:`dummy_threading` module is provided for situations where methods and functions in this module in the Python 2.x series are still supported by this module. -.. impl-detail:: - - Due to the :term:`Global Interpreter Lock`, in CPython only one thread - can execute Python code at once (even though certain performance-oriented - libraries might overcome this limitation). - If you want your application to make better of use of the computational - resources of multi-core machines, you are advised to use - :mod:`multiprocessing` or :class:`concurrent.futures.ProcessPoolExecutor`. - However, threading is still an appropriate model if you want to run - multiple I/O-bound tasks simultaneously. - This module defines the following functions and objects: @@ -59,6 +48,17 @@ This module defines the following functions and objects: returned. +.. function:: get_ident() + + Return the 'thread identifier' of the current thread. This is a nonzero + integer. Its value has no direct meaning; it is intended as a magic cookie + to be used e.g. to index a dictionary of thread-specific data. Thread + identifiers may be recycled when a thread exits and another thread is + created. + + .. versionadded:: 3.3 + + .. function:: enumerate() Return a list of all :class:`Thread` objects currently alive. The list @@ -174,7 +174,7 @@ This module defines the following functions and objects: *size* argument specifies the stack size to be used for subsequently created threads, and must be 0 (use platform or configured default) or a positive integer value of at least 32,768 (32kB). If changing the thread stack size is - unsupported, a :exc:`ThreadError` is raised. If the specified stack size is + unsupported, a :exc:`RuntimeError` is raised. If the specified stack size is invalid, a :exc:`ValueError` is raised and the stack size is unmodified. 32kB is currently the minimum supported stack size value to guarantee sufficient stack space for the interpreter itself. Note that some platforms may have @@ -239,10 +239,11 @@ called is terminated. A thread has a name. The name can be passed to the constructor, and read or changed through the :attr:`~Thread.name` attribute. -A thread can be flagged as a "daemon thread". The significance of this flag -is that the entire Python program exits when only daemon threads are left. -The initial value is inherited from the creating thread. The flag can be -set through the :attr:`~Thread.daemon` property. +A thread can be flagged as a "daemon thread". The significance of this flag is +that the entire Python program exits when only daemon threads are left. The +initial value is inherited from the creating thread. The flag can be set +through the :attr:`~Thread.daemon` property or the *daemon* constructor +argument. There is a "main thread" object; this corresponds to the initial thread of control in the Python program. It is not a daemon thread. @@ -255,7 +256,8 @@ daemonic, and cannot be :meth:`~Thread.join`\ ed. They are never deleted, since it is impossible to detect the termination of alien threads. -.. class:: Thread(group=None, target=None, name=None, args=(), kwargs={}) +.. class:: Thread(group=None, target=None, name=None, args=(), kwargs={}, + verbose=None, *, daemon=None) This constructor should always be called with keyword arguments. Arguments are: @@ -274,10 +276,19 @@ since it is impossible to detect the termination of alien threads. *kwargs* is a dictionary of keyword arguments for the target invocation. Defaults to ``{}``. + *verbose* is a flag used for debugging messages. + + If not ``None``, *daemon* explicitly sets whether the thread is daemonic. + If ``None`` (the default), the daemonic property is inherited from the + current thread. + If the subclass overrides the constructor, it must make sure to invoke the base class constructor (``Thread.__init__()``) before doing anything else to the thread. + .. versionchanged:: 3.3 + Added the *daemon* argument. + .. method:: start() Start the thread's activity. @@ -368,6 +379,18 @@ since it is impossible to detect the termination of alien threads. property instead. +.. impl-detail:: + + Due to the :term:`Global Interpreter Lock`, in CPython only one thread + can execute Python code at once (even though certain performance-oriented + libraries might overcome this limitation). + If you want your application to make better of use of the computational + resources of multi-core machines, you are advised to use + :mod:`multiprocessing` or :class:`concurrent.futures.ProcessPoolExecutor`. + However, threading is still an appropriate model if you want to run + multiple I/O-bound tasks simultaneously. + + .. _lock-objects: Lock Objects @@ -435,7 +458,7 @@ All methods are executed atomically. are blocked waiting for the lock to become unlocked, allow exactly one of them to proceed. - When invoked on an unlocked lock, a :exc:`ThreadError` is raised. + When invoked on an unlocked lock, a :exc:`RuntimeError` is raised. There is no return value. @@ -973,27 +996,3 @@ is equivalent to:: Currently, :class:`Lock`, :class:`RLock`, :class:`Condition`, :class:`Semaphore`, and :class:`BoundedSemaphore` objects may be used as :keyword:`with` statement context managers. - - -.. _threaded-imports: - -Importing in threaded code --------------------------- - -While the import machinery is thread-safe, there are two key restrictions on -threaded imports due to inherent limitations in the way that thread-safety is -provided: - -* Firstly, other than in the main module, an import should not have the - side effect of spawning a new thread and then waiting for that thread in - any way. Failing to abide by this restriction can lead to a deadlock if - the spawned thread directly or indirectly attempts to import a module. -* Secondly, all import attempts must be completed before the interpreter - starts shutting itself down. This can be most easily achieved by only - performing imports from non-daemon threads created through the threading - module. Daemon threads and threads created directly with the thread - module will require some other form of synchronization to ensure they do - not attempt imports after system shutdown has commenced. Failure to - abide by this restriction will lead to intermittent exceptions and - crashes during interpreter shutdown (as the late imports attempt to - access machinery which is no longer in a valid state). |