cpython-lru_cache-weakref: Doc/library/threading.rst annotate

annotate Doc/library/threading.rst @ 79675:c0a2294de787 2.7

Issue #16199: Backport 2to3 typo fix from 3.2.

author	Chris Jerdonek <chris.jerdonek@gmail.com>
date	Thu, 11 Oct 2012 16:15:46 -0700
parents	251463919f3c
children	8886d7ca159b

rev	line source
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	1 :mod:`threading` --- Higher-level threading interface
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	2 =====================================================
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	3
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	4 .. module:: threading
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	5 :synopsis: Higher-level threading interface.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	6
71952 b5674229d0f9 Backport source links from 3.x. Éric Araujo <merwok@netwok.org> parents: 68256 diff changeset	7 Source code: :source:`Lib/threading.py`
b5674229d0f9 Backport source links from 3.x. Éric Araujo <merwok@netwok.org> parents: 68256 diff changeset	8
b5674229d0f9 Backport source links from 3.x. Éric Araujo <merwok@netwok.org> parents: 68256 diff changeset	9 --------------
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	10
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	11 This module constructs higher-level threading interfaces on top of the lower
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	12 level :mod:`thread` module.
47248 9acb314b9072 Queue renaming reversal part 3: move module into place and Georg Brandl <georg@python.org> parents: 46939 diff changeset	13 See also the :mod:`mutex` and :mod:`Queue` modules.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	14
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	15 The :mod:`dummy_threading` module is provided for situations where
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	16 :mod:`threading` cannot be used because :mod:`thread` is missing.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	17
47601 8dc4312a2f75 add aliases to threading module Benjamin Peterson <benjamin@python.org> parents: 47598 diff changeset	18 .. note::
8dc4312a2f75 add aliases to threading module Benjamin Peterson <benjamin@python.org> parents: 47598 diff changeset	19
61572 0cb0fad514f3 Merged revisions 81163 via svnmerge from Victor Stinner <victor.stinner@haypocalc.com> parents: 56822 diff changeset	20 Starting with Python 2.6, this module provides :pep:`8` compliant aliases and
48942 bc585b4d4606 remove py3k warnings about the threading api; update docs Benjamin Peterson <benjamin@python.org> parents: 48297 diff changeset	21 properties to replace the ``camelCase`` names that were inspired by Java's
bc585b4d4606 remove py3k warnings about the threading api; update docs Benjamin Peterson <benjamin@python.org> parents: 48297 diff changeset	22 threading API. This updated API is compatible with that of the
bc585b4d4606 remove py3k warnings about the threading api; update docs Benjamin Peterson <benjamin@python.org> parents: 48297 diff changeset	23 :mod:`multiprocessing` module. However, no schedule has been set for the
bc585b4d4606 remove py3k warnings about the threading api; update docs Benjamin Peterson <benjamin@python.org> parents: 48297 diff changeset	24 deprecation of the ``camelCase`` names and they remain fully supported in
bc585b4d4606 remove py3k warnings about the threading api; update docs Benjamin Peterson <benjamin@python.org> parents: 48297 diff changeset	25 both Python 2.x and 3.x.
47601 8dc4312a2f75 add aliases to threading module Benjamin Peterson <benjamin@python.org> parents: 47598 diff changeset	26
52909 f3b26a729e82 Merged revisions 69578-69580,69901,69907,69994,70022-70023,70025-70026,70166,70273,70275,70342,70386-70387,70389-70390,70392-70393,70395,70397,70400,70418 via svnmerge Georg Brandl <georg@python.org> parents: 51809 diff changeset	27 .. note::
f3b26a729e82 Merged revisions 69578-69580,69901,69907,69994,70022-70023,70025-70026,70166,70273,70275,70342,70386-70387,70389-70390,70392-70393,70395,70397,70400,70418 via svnmerge Georg Brandl <georg@python.org> parents: 51809 diff changeset	28
f3b26a729e82 Merged revisions 69578-69580,69901,69907,69994,70022-70023,70025-70026,70166,70273,70275,70342,70386-70387,70389-70390,70392-70393,70395,70397,70400,70418 via svnmerge Georg Brandl <georg@python.org> parents: 51809 diff changeset	29 Starting with Python 2.5, several Thread methods raise :exc:`RuntimeError`
f3b26a729e82 Merged revisions 69578-69580,69901,69907,69994,70022-70023,70025-70026,70166,70273,70275,70342,70386-70387,70389-70390,70392-70393,70395,70397,70400,70418 via svnmerge Georg Brandl <georg@python.org> parents: 51809 diff changeset	30 instead of :exc:`AssertionError` if called erroneously.
f3b26a729e82 Merged revisions 69578-69580,69901,69907,69994,70022-70023,70025-70026,70166,70273,70275,70342,70386-70387,70389-70390,70392-70393,70395,70397,70400,70418 via svnmerge Georg Brandl <georg@python.org> parents: 51809 diff changeset	31
67408 26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	32 .. impl-detail::
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	33
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	34 Due to the :term:`Global Interpreter Lock`, in CPython only one thread
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	35 can execute Python code at once (even though certain performance-oriented
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	36 libraries might overcome this limitation).
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	37 If you want your application to make better of use of the computational
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	38 resources of multi-core machines, you are advised to use
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	39 :mod:`multiprocessing`. However, threading is still an appropriate model
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	40 if you want to run multiple I/O-bound tasks simultaneously.
26836e47dfb9 Merged revisions 87792 via svnmerge from Antoine Pitrou <solipsis@pitrou.net> parents: 67239 diff changeset	41
52909 f3b26a729e82 Merged revisions 69578-69580,69901,69907,69994,70022-70023,70025-70026,70166,70273,70275,70342,70386-70387,70389-70390,70392-70393,70395,70397,70400,70418 via svnmerge Georg Brandl <georg@python.org> parents: 51809 diff changeset	42
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	43 This module defines the following functions and objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	44
47598 c349f9fbc704 give the threading API PEP 8 names Benjamin Peterson <benjamin@python.org> parents: 47438 diff changeset	45 .. function:: active_count()
47601 8dc4312a2f75 add aliases to threading module Benjamin Peterson <benjamin@python.org> parents: 47598 diff changeset	46 activeCount()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	47
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	48 Return the number of :class:`Thread` objects currently alive. The returned
56822 c4c429b08a57 Merged revisions 74861-74863,74876,74896,74930,74933,74952-74953,75015,75019,75260-75263,75265-75266,75289 via svnmerge from Georg Brandl <georg@python.org> parents: 56819 diff changeset	49 count is equal to the length of the list returned by :func:`.enumerate`.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	50
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	51
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	52 .. function:: Condition()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	53 :noindex:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	54
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	55 A factory function that returns a new condition variable object. A condition
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	56 variable allows one or more threads to wait until they are notified by another
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	57 thread.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	58
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	59 See :ref:`condition-objects`.
ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	60
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	61
47598 c349f9fbc704 give the threading API PEP 8 names Benjamin Peterson <benjamin@python.org> parents: 47438 diff changeset	62 .. function:: current_thread()
47601 8dc4312a2f75 add aliases to threading module Benjamin Peterson <benjamin@python.org> parents: 47598 diff changeset	63 currentThread()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	64
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	65 Return the current :class:`Thread` object, corresponding to the caller's thread
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	66 of control. If the caller's thread of control was not created through the
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	67 :mod:`threading` module, a dummy thread object with limited functionality is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	68 returned.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	69
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	70
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	71 .. function:: enumerate()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	72
47598 c349f9fbc704 give the threading API PEP 8 names Benjamin Peterson <benjamin@python.org> parents: 47438 diff changeset	73 Return a list of all :class:`Thread` objects currently alive. The list
c349f9fbc704 give the threading API PEP 8 names Benjamin Peterson <benjamin@python.org> parents: 47438 diff changeset	74 includes daemonic threads, dummy thread objects created by
c349f9fbc704 give the threading API PEP 8 names Benjamin Peterson <benjamin@python.org> parents: 47438 diff changeset	75 :func:`current_thread`, and the main thread. It excludes terminated threads
c349f9fbc704 give the threading API PEP 8 names Benjamin Peterson <benjamin@python.org> parents: 47438 diff changeset	76 and threads that have not yet been started.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	77
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	78
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	79 .. function:: Event()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	80 :noindex:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	81
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	82 A factory function that returns a new event object. An event manages a flag
56817 6b05d48cca28 Merged revisions 74207 via svnmerge from Georg Brandl <georg@python.org> parents: 53569 diff changeset	83 that can be set to true with the :meth:`~Event.set` method and reset to false
6b05d48cca28 Merged revisions 74207 via svnmerge from Georg Brandl <georg@python.org> parents: 53569 diff changeset	84 with the :meth:`clear` method. The :meth:`wait` method blocks until the flag
6b05d48cca28 Merged revisions 74207 via svnmerge from Georg Brandl <georg@python.org> parents: 53569 diff changeset	85 is true.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	86
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	87 See :ref:`event-objects`.
ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	88
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	89
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	90 .. class:: local
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	91
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	92 A class that represents thread-local data. Thread-local data are data whose
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	93 values are thread specific. To manage thread-local data, just create an
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	94 instance of :class:`local` (or a subclass) and store attributes on it::
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	95
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	96 mydata = threading.local()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	97 mydata.x = 1
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	98
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	99 The instance's values will be different for separate threads.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	100
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	101 For more details and extensive examples, see the documentation string of the
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	102 :mod:`_threading_local` module.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	103
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	104 .. versionadded:: 2.4
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	105
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	106
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	107 .. function:: Lock()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	108
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	109 A factory function that returns a new primitive lock object. Once a thread has
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	110 acquired it, subsequent attempts to acquire it block, until it is released; any
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	111 thread may release it.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	112
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	113 See :ref:`lock-objects`.
ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	114
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	115
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	116 .. function:: RLock()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	117
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	118 A factory function that returns a new reentrant lock object. A reentrant lock
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	119 must be released by the thread that acquired it. Once a thread has acquired a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	120 reentrant lock, the same thread may acquire it again without blocking; the
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	121 thread must release it once for each time it has acquired it.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	122
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	123 See :ref:`rlock-objects`.
ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	124
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	125
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	126 .. function:: Semaphore([value])
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	127 :noindex:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	128
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	129 A factory function that returns a new semaphore object. A semaphore manages a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	130 counter representing the number of :meth:`release` calls minus the number of
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	131 :meth:`acquire` calls, plus an initial value. The :meth:`acquire` method blocks
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	132 if necessary until it can return without making the counter negative. If not
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	133 given, value defaults to 1.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	134
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	135 See :ref:`semaphore-objects`.
ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	136
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	137
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	138 .. function:: BoundedSemaphore([value])
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	139
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	140 A factory function that returns a new bounded semaphore object. A bounded
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	141 semaphore checks to make sure its current value doesn't exceed its initial
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	142 value. If it does, :exc:`ValueError` is raised. In most situations semaphores
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	143 are used to guard resources with limited capacity. If the semaphore is released
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	144 too many times it's a sign of a bug. If not given, value defaults to 1.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	145
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	146
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	147 .. class:: Thread
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	148 :noindex:
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9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	150 A class that represents a thread of control. This class can be safely
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	151 subclassed in a limited fashion.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	152
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	153 See :ref:`thread-objects`.
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42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	155
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	156 .. class:: Timer
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	157 :noindex:
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	158
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	159 A thread that executes a function after a specified interval has passed.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	160
65127 ff734f225b47 Merged revisions 82798,82805,83659,83977,84015,84018,84141,84264,84326-84327,84480,84482,84484,84530-84531,84553,84619,84915-84916 via svnmerge from Georg Brandl <georg@python.org> parents: 63155 diff changeset	161 See :ref:`timer-objects`.
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42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	163
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	164 .. function:: settrace(func)
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	165
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	166 .. index:: single: trace function
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	167
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	168 Set a trace function for all threads started from the :mod:`threading` module.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	169 The func will be passed to :func:`sys.settrace` for each thread, before its
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	170 :meth:`run` method is called.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	171
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	172 .. versionadded:: 2.3
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	173
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	174
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	175 .. function:: setprofile(func)
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	176
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	177 .. index:: single: profile function
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	178
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	179 Set a profile function for all threads started from the :mod:`threading` module.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	180 The func will be passed to :func:`sys.setprofile` for each thread, before its
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	181 :meth:`run` method is called.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	182
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	183 .. versionadded:: 2.3
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	184
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	185
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	186 .. function:: stack_size([size])
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	187
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	188 Return the thread stack size used when creating new threads. The optional
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	189 size argument specifies the stack size to be used for subsequently created
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	190 threads, and must be 0 (use platform or configured default) or a positive
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	191 integer value of at least 32,768 (32kB). If changing the thread stack size is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	192 unsupported, a :exc:`ThreadError` is raised. If the specified stack size is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	193 invalid, a :exc:`ValueError` is raised and the stack size is unmodified. 32kB
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	194 is currently the minimum supported stack size value to guarantee sufficient
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	195 stack space for the interpreter itself. Note that some platforms may have
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	196 particular restrictions on values for the stack size, such as requiring a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	197 minimum stack size > 32kB or requiring allocation in multiples of the system
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	198 memory page size - platform documentation should be referred to for more
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	199 information (4kB pages are common; using multiples of 4096 for the stack size is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	200 the suggested approach in the absence of more specific information).
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	201 Availability: Windows, systems with POSIX threads.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	202
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	203 .. versionadded:: 2.5
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	204
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	205 Detailed interfaces for the objects are documented below.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	206
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	207 The design of this module is loosely based on Java's threading model. However,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	208 where Java makes locks and condition variables basic behavior of every object,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	209 they are separate objects in Python. Python's :class:`Thread` class supports a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	210 subset of the behavior of Java's Thread class; currently, there are no
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	211 priorities, no thread groups, and threads cannot be destroyed, stopped,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	212 suspended, resumed, or interrupted. The static methods of Java's Thread class,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	213 when implemented, are mapped to module-level functions.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	214
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	215 All of the methods described below are executed atomically.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	216
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	217
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	218 .. _thread-objects:
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82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	223 This class represents an activity that is run in a separate thread of control.
82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	224 There are two ways to specify the activity: by passing a callable object to the
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82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	226 methods (except for the constructor) should be overridden in a subclass. In
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82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	235 stops being alive when its :meth:`run` method terminates -- either normally, or
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3174d5ba46e3 Merged revisions 82571,82603,82845,82852,82953,82981,83013,83077,83082,83164,83251 via svnmerge from Georg Brandl <georg@python.org> parents: 61803 diff changeset	352 until just after the :meth:`run` method terminates. The module function
56822 c4c429b08a57 Merged revisions 74861-74863,74876,74896,74930,74933,74952-74953,75015,75019,75260-75263,75265-75266,75289 via svnmerge from Georg Brandl <georg@python.org> parents: 56819 diff changeset	353 :func:`.enumerate` returns a list of all alive threads.
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	354
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	355 .. method:: isDaemon()
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	356 setDaemon()
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	357
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	358 Old API for :attr:`~Thread.daemon`.
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	359
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	360 .. attribute:: daemon
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	361
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	362 A boolean value indicating whether this thread is a daemon thread (True)
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	363 or not (False). This must be set before :meth:`start` is called,
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	364 otherwise :exc:`RuntimeError` is raised. Its initial value is inherited
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	365 from the creating thread; the main thread is not a daemon thread and
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	366 therefore all threads created in the main thread default to :attr:`daemon`
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	367 = ``False``.
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	368
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	369 The entire Python program exits when no alive non-daemon threads are left.
49677 82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	370
82ccc7e77ec5 Merged revisions 66801,66803-66804,66813,66854-66856,66866,66870-66872,66874,66887,66903,66905,66911,66913,66927,66932,66938,66942,66962,66964,66973-66974,66977,66992,66998-66999,67002,67005,67007,67028,67040-67041,67044,67070,67089,67091,67101,67117-67119,67123-67124 via svnmerge from Georg Brandl <georg@python.org> parents: 48942 diff changeset	371
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	372 .. _lock-objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	373
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	374 Lock Objects
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	375 ------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	376
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	377 A primitive lock is a synchronization primitive that is not owned by a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	378 particular thread when locked. In Python, it is currently the lowest level
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	379 synchronization primitive available, implemented directly by the :mod:`thread`
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	380 extension module.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	381
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	382 A primitive lock is in one of two states, "locked" or "unlocked". It is created
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	383 in the unlocked state. It has two basic methods, :meth:`acquire` and
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	384 :meth:`release`. When the state is unlocked, :meth:`acquire` changes the state
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	385 to locked and returns immediately. When the state is locked, :meth:`acquire`
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	386 blocks until a call to :meth:`release` in another thread changes it to unlocked,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	387 then the :meth:`acquire` call resets it to locked and returns. The
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	388 :meth:`release` method should only be called in the locked state; it changes the
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	389 state to unlocked and returns immediately. If an attempt is made to release an
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	390 unlocked lock, a :exc:`RuntimeError` will be raised.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	391
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	392 When more than one thread is blocked in :meth:`acquire` waiting for the state to
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	393 turn to unlocked, only one thread proceeds when a :meth:`release` call resets
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	394 the state to unlocked; which one of the waiting threads proceeds is not defined,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	395 and may vary across implementations.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	396
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	397 All methods are executed atomically.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	398
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	399
67239 53db290e46ef Issue 10789: Correct threading.Lock.acquire signature. Terry Reedy <tjreedy@udel.edu> parents: 66459 diff changeset	400 .. method:: Lock.acquire([blocking])
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	401
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	402 Acquire a lock, blocking or non-blocking.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	403
77011 251463919f3c #14823: Simplify threading.Lock.acquire argument discussion. R David Murray <rdmurray@bitdance.com> parents: 76129 diff changeset	404 When invoked with the blocking argument set to ``True`` (the default),
251463919f3c #14823: Simplify threading.Lock.acquire argument discussion. R David Murray <rdmurray@bitdance.com> parents: 76129 diff changeset	405 block until the lock is unlocked, then set it to locked and return ``True``.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	406
77011 251463919f3c #14823: Simplify threading.Lock.acquire argument discussion. R David Murray <rdmurray@bitdance.com> parents: 76129 diff changeset	407 When invoked with the blocking argument set to ``False``, do not block.
251463919f3c #14823: Simplify threading.Lock.acquire argument discussion. R David Murray <rdmurray@bitdance.com> parents: 76129 diff changeset	408 If a call with blocking set to ``True`` would block, return ``False``
251463919f3c #14823: Simplify threading.Lock.acquire argument discussion. R David Murray <rdmurray@bitdance.com> parents: 76129 diff changeset	409 immediately; otherwise, set the lock to locked and return ``True``.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	410
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	411
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	412 .. method:: Lock.release()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	413
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	414 Release a lock.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	415
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	416 When the lock is locked, reset it to unlocked, and return. If any other threads
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	417 are blocked waiting for the lock to become unlocked, allow exactly one of them
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	418 to proceed.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	419
76129 efeca6ff2751 Issue #14502: release() and unlocked lock generates a ThreadError Sandro Tosi <sandro.tosi@gmail.com> parents: 73523 diff changeset	420 When invoked on an unlocked lock, a :exc:`ThreadError` is raised.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	421
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	422 There is no return value.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	423
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	424
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	425 .. _rlock-objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	426
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	427 RLock Objects
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	428 -------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	429
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	430 A reentrant lock is a synchronization primitive that may be acquired multiple
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	431 times by the same thread. Internally, it uses the concepts of "owning thread"
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	432 and "recursion level" in addition to the locked/unlocked state used by primitive
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	433 locks. In the locked state, some thread owns the lock; in the unlocked state,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	434 no thread owns it.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	435
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	436 To lock the lock, a thread calls its :meth:`acquire` method; this returns once
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	437 the thread owns the lock. To unlock the lock, a thread calls its
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	438 :meth:`release` method. :meth:`acquire`/:meth:`release` call pairs may be
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	439 nested; only the final :meth:`release` (the :meth:`release` of the outermost
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	440 pair) resets the lock to unlocked and allows another thread blocked in
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	441 :meth:`acquire` to proceed.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	442
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	443
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	444 .. method:: RLock.acquire([blocking=1])
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	445
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	446 Acquire a lock, blocking or non-blocking.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	447
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	448 When invoked without arguments: if this thread already owns the lock, increment
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	449 the recursion level by one, and return immediately. Otherwise, if another
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	450 thread owns the lock, block until the lock is unlocked. Once the lock is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	451 unlocked (not owned by any thread), then grab ownership, set the recursion level
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	452 to one, and return. If more than one thread is blocked waiting until the lock
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	453 is unlocked, only one at a time will be able to grab ownership of the lock.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	454 There is no return value in this case.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	455
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	456 When invoked with the blocking argument set to true, do the same thing as when
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	457 called without arguments, and return true.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	458
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	459 When invoked with the blocking argument set to false, do not block. If a call
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	460 without an argument would block, return false immediately; otherwise, do the
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	461 same thing as when called without arguments, and return true.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	462
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	463
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	464 .. method:: RLock.release()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	465
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	466 Release a lock, decrementing the recursion level. If after the decrement it is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	467 zero, reset the lock to unlocked (not owned by any thread), and if any other
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	468 threads are blocked waiting for the lock to become unlocked, allow exactly one
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	469 of them to proceed. If after the decrement the recursion level is still
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	470 nonzero, the lock remains locked and owned by the calling thread.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	471
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	472 Only call this method when the calling thread owns the lock. A
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	473 :exc:`RuntimeError` is raised if this method is called when the lock is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	474 unlocked.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	475
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	476 There is no return value.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	477
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	478
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	479 .. _condition-objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	480
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	481 Condition Objects
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	482 -----------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	483
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	484 A condition variable is always associated with some kind of lock; this can be
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	485 passed in or one will be created by default. (Passing one in is useful when
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	486 several condition variables must share the same lock.)
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	487
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	488 A condition variable has :meth:`acquire` and :meth:`release` methods that call
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	489 the corresponding methods of the associated lock. It also has a :meth:`wait`
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	490 method, and :meth:`notify` and :meth:`notifyAll` methods. These three must only
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	491 be called when the calling thread has acquired the lock, otherwise a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	492 :exc:`RuntimeError` is raised.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	493
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	494 The :meth:`wait` method releases the lock, and then blocks until it is awakened
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	495 by a :meth:`notify` or :meth:`notifyAll` call for the same condition variable in
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	496 another thread. Once awakened, it re-acquires the lock and returns. It is also
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	497 possible to specify a timeout.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	498
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	499 The :meth:`notify` method wakes up one of the threads waiting for the condition
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	500 variable, if any are waiting. The :meth:`notifyAll` method wakes up all threads
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	501 waiting for the condition variable.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	502
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	503 Note: the :meth:`notify` and :meth:`notifyAll` methods don't release the lock;
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	504 this means that the thread or threads awakened will not return from their
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	505 :meth:`wait` call immediately, but only when the thread that called
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	506 :meth:`notify` or :meth:`notifyAll` finally relinquishes ownership of the lock.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	507
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	508 Tip: the typical programming style using condition variables uses the lock to
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	509 synchronize access to some shared state; threads that are interested in a
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	510 particular change of state call :meth:`wait` repeatedly until they see the
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	511 desired state, while threads that modify the state call :meth:`notify` or
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	512 :meth:`notifyAll` when they change the state in such a way that it could
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	513 possibly be a desired state for one of the waiters. For example, the following
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	514 code is a generic producer-consumer situation with unlimited buffer capacity::
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	515
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	516 # Consume one item
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	517 cv.acquire()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	518 while not an_item_is_available():
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	519 cv.wait()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	520 get_an_available_item()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	521 cv.release()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	522
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	523 # Produce one item
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	524 cv.acquire()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	525 make_an_item_available()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	526 cv.notify()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	527 cv.release()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	528
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	529 To choose between :meth:`notify` and :meth:`notifyAll`, consider whether one
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	530 state change can be interesting for only one or several waiting threads. E.g.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	531 in a typical producer-consumer situation, adding one item to the buffer only
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	532 needs to wake up one consumer thread.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	533
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	534
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	535 .. class:: Condition([lock])
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	536
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	537 If the lock argument is given and not ``None``, it must be a :class:`Lock`
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	538 or :class:`RLock` object, and it is used as the underlying lock. Otherwise,
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	539 a new :class:`RLock` object is created and used as the underlying lock.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	540
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	541 .. method:: acquire(*args)
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	542
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	543 Acquire the underlying lock. This method calls the corresponding method on
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	544 the underlying lock; the return value is whatever that method returns.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	545
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	546 .. method:: release()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	547
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	548 Release the underlying lock. This method calls the corresponding method on
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	549 the underlying lock; there is no return value.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	550
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	551 .. method:: wait([timeout])
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	552
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	553 Wait until notified or until a timeout occurs. If the calling thread has not
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	554 acquired the lock when this method is called, a :exc:`RuntimeError` is raised.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	555
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	556 This method releases the underlying lock, and then blocks until it is
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	557 awakened by a :meth:`notify` or :meth:`notifyAll` call for the same
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	558 condition variable in another thread, or until the optional timeout
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	559 occurs. Once awakened or timed out, it re-acquires the lock and returns.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	560
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	561 When the timeout argument is present and not ``None``, it should be a
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	562 floating point number specifying a timeout for the operation in seconds
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	563 (or fractions thereof).
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	564
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	565 When the underlying lock is an :class:`RLock`, it is not released using
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	566 its :meth:`release` method, since this may not actually unlock the lock
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	567 when it was acquired multiple times recursively. Instead, an internal
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	568 interface of the :class:`RLock` class is used, which really unlocks it
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	569 even when it has been recursively acquired several times. Another internal
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	570 interface is then used to restore the recursion level when the lock is
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	571 reacquired.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	572
73523 63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	573 .. method:: notify(n=1)
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	574
73523 63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	575 By default, wake up one thread waiting on this condition, if any. If the
63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	576 calling thread has not acquired the lock when this method is called, a
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	577 :exc:`RuntimeError` is raised.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	578
73523 63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	579 This method wakes up at most n of the threads waiting for the condition
63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	580 variable; it is a no-op if no threads are waiting.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	581
73523 63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	582 The current implementation wakes up exactly n threads, if at least n
63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	583 threads are waiting. However, it's not safe to rely on this behavior.
63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	584 A future, optimized implementation may occasionally wake up more than
63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	585 n threads.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	586
73523 63a00d019bb2 Closes issue 12767: document the argument of threading.Condition.notify Eli Bendersky <eliben@gmail.com> parents: 71952 diff changeset	587 Note: an awakened thread does not actually return from its :meth:`wait`
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	588 call until it can reacquire the lock. Since :meth:`notify` does not
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	589 release the lock, its caller should.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	590
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	591 .. method:: notify_all()
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	592 notifyAll()
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	593
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	594 Wake up all threads waiting on this condition. This method acts like
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	595 :meth:`notify`, but wakes up all waiting threads instead of one. If the
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	596 calling thread has not acquired the lock when this method is called, a
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	597 :exc:`RuntimeError` is raised.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	598
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	599
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	600 .. _semaphore-objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	601
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	602 Semaphore Objects
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	603 -----------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	604
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	605 This is one of the oldest synchronization primitives in the history of computer
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	606 science, invented by the early Dutch computer scientist Edsger W. Dijkstra (he
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	607 used :meth:`P` and :meth:`V` instead of :meth:`acquire` and :meth:`release`).
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	608
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	609 A semaphore manages an internal counter which is decremented by each
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	610 :meth:`acquire` call and incremented by each :meth:`release` call. The counter
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	611 can never go below zero; when :meth:`acquire` finds that it is zero, it blocks,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	612 waiting until some other thread calls :meth:`release`.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	613
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	614
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	615 .. class:: Semaphore([value])
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	616
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	617 The optional argument gives the initial value for the internal counter; it
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	618 defaults to ``1``. If the value given is less than 0, :exc:`ValueError` is
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	619 raised.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	620
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	621 .. method:: acquire([blocking])
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	622
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	623 Acquire a semaphore.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	624
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	625 When invoked without arguments: if the internal counter is larger than
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	626 zero on entry, decrement it by one and return immediately. If it is zero
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	627 on entry, block, waiting until some other thread has called
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	628 :meth:`release` to make it larger than zero. This is done with proper
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	629 interlocking so that if multiple :meth:`acquire` calls are blocked,
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	630 :meth:`release` will wake exactly one of them up. The implementation may
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	631 pick one at random, so the order in which blocked threads are awakened
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	632 should not be relied on. There is no return value in this case.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	633
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	634 When invoked with blocking set to true, do the same thing as when called
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	635 without arguments, and return true.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	636
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	637 When invoked with blocking set to false, do not block. If a call
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	638 without an argument would block, return false immediately; otherwise, do
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	639 the same thing as when called without arguments, and return true.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	640
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	641 .. method:: release()
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	642
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	643 Release a semaphore, incrementing the internal counter by one. When it
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	644 was zero on entry and another thread is waiting for it to become larger
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	645 than zero again, wake up that thread.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	646
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	647
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	648 .. _semaphore-examples:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	649
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	650 :class:`Semaphore` Example
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	651 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	652
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	653 Semaphores are often used to guard resources with limited capacity, for example,
67486 e4d07a6f7abf Merged revisions 87807,87820,87831,87859 via svnmerge from Georg Brandl <georg@python.org> parents: 67408 diff changeset	654 a database server. In any situation where the size of the resource is fixed,
e4d07a6f7abf Merged revisions 87807,87820,87831,87859 via svnmerge from Georg Brandl <georg@python.org> parents: 67408 diff changeset	655 you should use a bounded semaphore. Before spawning any worker threads, your
e4d07a6f7abf Merged revisions 87807,87820,87831,87859 via svnmerge from Georg Brandl <georg@python.org> parents: 67408 diff changeset	656 main thread would initialize the semaphore::
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	657
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	658 maxconnections = 5
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	659 ...
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	660 pool_sema = BoundedSemaphore(value=maxconnections)
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	661
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	662 Once spawned, worker threads call the semaphore's acquire and release methods
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	663 when they need to connect to the server::
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	664
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	665 pool_sema.acquire()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	666 conn = connectdb()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	667 ... use connection ...
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	668 conn.close()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	669 pool_sema.release()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	670
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	671 The use of a bounded semaphore reduces the chance that a programming error which
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	672 causes the semaphore to be released more than it's acquired will go undetected.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	673
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	674
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	675 .. _event-objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	676
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	677 Event Objects
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	678 -------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	679
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	680 This is one of the simplest mechanisms for communication between threads: one
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	681 thread signals an event and other threads wait for it.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	682
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	683 An event object manages an internal flag that can be set to true with the
56817 6b05d48cca28 Merged revisions 74207 via svnmerge from Georg Brandl <georg@python.org> parents: 53569 diff changeset	684 :meth:`~Event.set` method and reset to false with the :meth:`clear` method. The
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	685 :meth:`wait` method blocks until the flag is true.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	686
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	687
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	688 .. class:: Event()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	689
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	690 The internal flag is initially false.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	691
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	692 .. method:: is_set()
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	693 isSet()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	694
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	695 Return true if and only if the internal flag is true.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	696
61730 3d0ae8ef0044 Merged revisions 77741 via svnmerge from Georg Brandl <georg@python.org> parents: 61572 diff changeset	697 .. versionchanged:: 2.6
3d0ae8ef0044 Merged revisions 77741 via svnmerge from Georg Brandl <georg@python.org> parents: 61572 diff changeset	698 The ``is_set()`` syntax is new.
3d0ae8ef0044 Merged revisions 77741 via svnmerge from Georg Brandl <georg@python.org> parents: 61572 diff changeset	699
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	700 .. method:: set()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	701
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	702 Set the internal flag to true. All threads waiting for it to become true
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	703 are awakened. Threads that call :meth:`wait` once the flag is true will
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	704 not block at all.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	705
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	706 .. method:: clear()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	707
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	708 Reset the internal flag to false. Subsequently, threads calling
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	709 :meth:`wait` will block until :meth:`.set` is called to set the internal
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	710 flag to true again.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	711
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	712 .. method:: wait([timeout])
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	713
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	714 Block until the internal flag is true. If the internal flag is true on
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	715 entry, return immediately. Otherwise, block until another thread calls
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	716 :meth:`.set` to set the flag to true, or until the optional timeout
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	717 occurs.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	718
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	719 When the timeout argument is present and not ``None``, it should be a
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	720 floating point number specifying a timeout for the operation in seconds
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	721 (or fractions thereof).
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	722
55450 42db1cf39afd Move member descriptions inside the classes. Georg Brandl <georg@python.org> parents: 55447 diff changeset	723 This method returns the internal flag on exit, so it will always return
42db1cf39afd Move member descriptions inside the classes. Georg Brandl <georg@python.org> parents: 55447 diff changeset	724 ``True`` except if a timeout is given and the operation times out.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	725
55450 42db1cf39afd Move member descriptions inside the classes. Georg Brandl <georg@python.org> parents: 55447 diff changeset	726 .. versionchanged:: 2.7
42db1cf39afd Move member descriptions inside the classes. Georg Brandl <georg@python.org> parents: 55447 diff changeset	727 Previously, the method always returned ``None``.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	728
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	729
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	730 .. _timer-objects:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	731
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	732 Timer Objects
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	733 -------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	734
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	735 This class represents an action that should be run only after a certain amount
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	736 of time has passed --- a timer. :class:`Timer` is a subclass of :class:`Thread`
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	737 and as such also functions as an example of creating custom threads.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	738
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	739 Timers are started, as with threads, by calling their :meth:`start` method. The
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	740 timer can be stopped (before its action has begun) by calling the :meth:`cancel`
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	741 method. The interval the timer will wait before executing its action may not be
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	742 exactly the same as the interval specified by the user.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	743
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	744 For example::
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	745
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	746 def hello():
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	747 print "hello, world"
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	748
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	749 t = Timer(30.0, hello)
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	750 t.start() # after 30 seconds, "hello, world" will be printed
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	751
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	752
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	753 .. class:: Timer(interval, function, args=[], kwargs={})
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	754
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	755 Create a timer that will run function with arguments args and keyword
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	756 arguments kwargs, after interval seconds have passed.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	757
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	758 .. method:: cancel()
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	759
56819 9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	760 Stop the timer, and cancel the execution of the timer's action. This will
9b24d010133f Merged revisions 74210,74239,74252-74253,74256,74258-74261,74332-74333,74404,74411,74445,74465,74467,74488 via svnmerge from Georg Brandl <georg@python.org> parents: 56817 diff changeset	761 only work if the timer is still in its waiting stage.
42604 9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	762
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	763
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	764 .. _with-locks:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	765
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	766 Using locks, conditions, and semaphores in the :keyword:`with` statement
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	767 ------------------------------------------------------------------------
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	768
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	769 All of the objects provided by this module that have :meth:`acquire` and
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	770 :meth:`release` methods can be used as context managers for a :keyword:`with`
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	771 statement. The :meth:`acquire` method will be called when the block is entered,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	772 and :meth:`release` will be called when the block is exited.
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	773
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	774 Currently, :class:`Lock`, :class:`RLock`, :class:`Condition`,
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	775 :class:`Semaphore`, and :class:`BoundedSemaphore` objects may be used as
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	776 :keyword:`with` statement context managers. For example::
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	777
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	778 import threading
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	779
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	780 some_rlock = threading.RLock()
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	781
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	782 with some_rlock:
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	783 print "some_rlock is locked while this executes"
9e1529bf0442 Move the 3k reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	784
45743 9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	785
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	786 .. _threaded-imports:
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	787
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	788 Importing in threaded code
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	789 --------------------------
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	790
66459 37b37b6a8972 Merged revisions 85731,85735 via svnmerge from Georg Brandl <georg@python.org> parents: 65995 diff changeset	791 While the import machinery is thread-safe, there are two key restrictions on
37b37b6a8972 Merged revisions 85731,85735 via svnmerge from Georg Brandl <georg@python.org> parents: 65995 diff changeset	792 threaded imports due to inherent limitations in the way that thread-safety is
37b37b6a8972 Merged revisions 85731,85735 via svnmerge from Georg Brandl <georg@python.org> parents: 65995 diff changeset	793 provided:
45743 9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	794
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	795 * Firstly, other than in the main module, an import should not have the
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	796 side effect of spawning a new thread and then waiting for that thread in
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	797 any way. Failing to abide by this restriction can lead to a deadlock if
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	798 the spawned thread directly or indirectly attempts to import a module.
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	799 * Secondly, all import attempts must be completed before the interpreter
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	800 starts shutting itself down. This can be most easily achieved by only
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	801 performing imports from non-daemon threads created through the threading
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	802 module. Daemon threads and threads created directly with the thread
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	803 module will require some other form of synchronization to ensure they do
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	804 not attempt imports after system shutdown has commenced. Failure to
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	805 abide by this restriction will lead to intermittent exceptions and
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	806 crashes during interpreter shutdown (as the late imports attempt to
9395a22a966a #1720705: add docs about import/threading interaction, wording by Nick. Georg Brandl <georg@python.org> parents: 45522 diff changeset	807 access machinery which is no longer in a valid state).

Mercurial > cpython-lru_cache-weakref

annotate Doc/library/threading.rst @ 79675:c0a2294de787 2.7