450 lines
13 KiB
Python
450 lines
13 KiB
Python
#
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# Module implementing synchronization primitives
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#
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# multiprocessing/synchronize.py
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#
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# Copyright (c) 2006-2008, R Oudkerk
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# Licensed to PSF under a Contributor Agreement.
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#
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from __future__ import absolute_import
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__all__ = [
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'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition', 'Event',
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]
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import itertools
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import os
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import signal
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import sys
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import threading
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from ._ext import _billiard, ensure_SemLock
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from .five import range, monotonic
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from .process import current_process
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from .util import Finalize, register_after_fork, debug
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from .forking import assert_spawning, Popen
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from .compat import bytes, closerange
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# Try to import the mp.synchronize module cleanly, if it fails
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# raise ImportError for platforms lacking a working sem_open implementation.
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# See issue 3770
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ensure_SemLock()
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#
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# Constants
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#
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RECURSIVE_MUTEX, SEMAPHORE = list(range(2))
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SEM_VALUE_MAX = _billiard.SemLock.SEM_VALUE_MAX
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try:
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sem_unlink = _billiard.SemLock.sem_unlink
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except AttributeError: # pragma: no cover
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try:
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# Py3.4+ implements sem_unlink and the semaphore must be named
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from _multiprocessing import sem_unlink # noqa
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except ImportError:
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sem_unlink = None # noqa
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#
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# Base class for semaphores and mutexes; wraps `_billiard.SemLock`
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#
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def _semname(sl):
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try:
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return sl.name
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except AttributeError:
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pass
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class SemLock(object):
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_counter = itertools.count()
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def __init__(self, kind, value, maxvalue):
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from .forking import _forking_is_enabled
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unlink_immediately = _forking_is_enabled or sys.platform == 'win32'
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if sem_unlink:
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sl = self._semlock = _billiard.SemLock(
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kind, value, maxvalue, self._make_name(), unlink_immediately)
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else:
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sl = self._semlock = _billiard.SemLock(kind, value, maxvalue)
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debug('created semlock with handle %s', sl.handle)
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self._make_methods()
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if sem_unlink:
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if sys.platform != 'win32':
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def _after_fork(obj):
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obj._semlock._after_fork()
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register_after_fork(self, _after_fork)
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if _semname(self._semlock) is not None:
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# We only get here if we are on Unix with forking
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# disabled. When the object is garbage collected or the
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# process shuts down we unlink the semaphore name
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Finalize(self, sem_unlink, (self._semlock.name,),
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exitpriority=0)
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# In case of abnormal termination unlink semaphore name
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_cleanup_semaphore_if_leaked(self._semlock.name)
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def _make_methods(self):
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self.acquire = self._semlock.acquire
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self.release = self._semlock.release
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def __enter__(self):
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return self._semlock.__enter__()
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def __exit__(self, *args):
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return self._semlock.__exit__(*args)
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def __getstate__(self):
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assert_spawning(self)
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sl = self._semlock
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state = (Popen.duplicate_for_child(sl.handle), sl.kind, sl.maxvalue)
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try:
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state += (sl.name, )
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except AttributeError:
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pass
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return state
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def __setstate__(self, state):
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self._semlock = _billiard.SemLock._rebuild(*state)
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debug('recreated blocker with handle %r', state[0])
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self._make_methods()
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@staticmethod
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def _make_name():
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return '/%s-%s-%s' % (current_process()._semprefix,
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os.getpid(), next(SemLock._counter))
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class Semaphore(SemLock):
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def __init__(self, value=1):
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SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX)
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def get_value(self):
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return self._semlock._get_value()
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def __repr__(self):
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try:
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value = self._semlock._get_value()
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except Exception:
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value = 'unknown'
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return '<Semaphore(value=%s)>' % value
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class BoundedSemaphore(Semaphore):
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def __init__(self, value=1):
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SemLock.__init__(self, SEMAPHORE, value, value)
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def __repr__(self):
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try:
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value = self._semlock._get_value()
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except Exception:
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value = 'unknown'
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return '<BoundedSemaphore(value=%s, maxvalue=%s)>' % \
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(value, self._semlock.maxvalue)
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class Lock(SemLock):
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'''
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Non-recursive lock.
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'''
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def __init__(self):
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SemLock.__init__(self, SEMAPHORE, 1, 1)
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def __repr__(self):
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try:
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if self._semlock._is_mine():
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name = current_process().name
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if threading.currentThread().name != 'MainThread':
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name += '|' + threading.currentThread().name
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elif self._semlock._get_value() == 1:
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name = 'None'
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elif self._semlock._count() > 0:
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name = 'SomeOtherThread'
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else:
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name = 'SomeOtherProcess'
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except Exception:
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name = 'unknown'
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return '<Lock(owner=%s)>' % name
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class RLock(SemLock):
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'''
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Recursive lock
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'''
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def __init__(self):
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SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1)
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def __repr__(self):
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try:
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if self._semlock._is_mine():
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name = current_process().name
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if threading.currentThread().name != 'MainThread':
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name += '|' + threading.currentThread().name
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count = self._semlock._count()
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elif self._semlock._get_value() == 1:
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name, count = 'None', 0
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elif self._semlock._count() > 0:
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name, count = 'SomeOtherThread', 'nonzero'
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else:
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name, count = 'SomeOtherProcess', 'nonzero'
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except Exception:
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name, count = 'unknown', 'unknown'
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return '<RLock(%s, %s)>' % (name, count)
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class Condition(object):
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'''
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Condition variable
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'''
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def __init__(self, lock=None):
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self._lock = lock or RLock()
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self._sleeping_count = Semaphore(0)
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self._woken_count = Semaphore(0)
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self._wait_semaphore = Semaphore(0)
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self._make_methods()
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def __getstate__(self):
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assert_spawning(self)
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return (self._lock, self._sleeping_count,
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self._woken_count, self._wait_semaphore)
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def __setstate__(self, state):
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(self._lock, self._sleeping_count,
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self._woken_count, self._wait_semaphore) = state
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self._make_methods()
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def __enter__(self):
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return self._lock.__enter__()
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def __exit__(self, *args):
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return self._lock.__exit__(*args)
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def _make_methods(self):
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self.acquire = self._lock.acquire
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self.release = self._lock.release
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def __repr__(self):
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try:
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num_waiters = (self._sleeping_count._semlock._get_value() -
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self._woken_count._semlock._get_value())
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except Exception:
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num_waiters = 'unkown'
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return '<Condition(%s, %s)>' % (self._lock, num_waiters)
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def wait(self, timeout=None):
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assert self._lock._semlock._is_mine(), \
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'must acquire() condition before using wait()'
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# indicate that this thread is going to sleep
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self._sleeping_count.release()
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# release lock
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count = self._lock._semlock._count()
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for i in range(count):
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self._lock.release()
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try:
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# wait for notification or timeout
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ret = self._wait_semaphore.acquire(True, timeout)
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finally:
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# indicate that this thread has woken
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self._woken_count.release()
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# reacquire lock
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for i in range(count):
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self._lock.acquire()
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return ret
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def notify(self):
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assert self._lock._semlock._is_mine(), 'lock is not owned'
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assert not self._wait_semaphore.acquire(False)
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# to take account of timeouts since last notify() we subtract
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# woken_count from sleeping_count and rezero woken_count
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while self._woken_count.acquire(False):
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res = self._sleeping_count.acquire(False)
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assert res
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if self._sleeping_count.acquire(False): # try grabbing a sleeper
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self._wait_semaphore.release() # wake up one sleeper
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self._woken_count.acquire() # wait for sleeper to wake
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# rezero _wait_semaphore in case a timeout just happened
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self._wait_semaphore.acquire(False)
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def notify_all(self):
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assert self._lock._semlock._is_mine(), 'lock is not owned'
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assert not self._wait_semaphore.acquire(False)
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# to take account of timeouts since last notify*() we subtract
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# woken_count from sleeping_count and rezero woken_count
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while self._woken_count.acquire(False):
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res = self._sleeping_count.acquire(False)
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assert res
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sleepers = 0
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while self._sleeping_count.acquire(False):
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self._wait_semaphore.release() # wake up one sleeper
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sleepers += 1
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if sleepers:
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for i in range(sleepers):
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self._woken_count.acquire() # wait for a sleeper to wake
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# rezero wait_semaphore in case some timeouts just happened
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while self._wait_semaphore.acquire(False):
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pass
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def wait_for(self, predicate, timeout=None):
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result = predicate()
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if result:
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return result
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if timeout is not None:
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endtime = monotonic() + timeout
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else:
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endtime = None
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waittime = None
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while not result:
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if endtime is not None:
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waittime = endtime - monotonic()
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if waittime <= 0:
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break
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self.wait(waittime)
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result = predicate()
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return result
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class Event(object):
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def __init__(self):
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self._cond = Condition(Lock())
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self._flag = Semaphore(0)
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def is_set(self):
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self._cond.acquire()
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try:
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if self._flag.acquire(False):
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self._flag.release()
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return True
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return False
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finally:
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self._cond.release()
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def set(self):
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self._cond.acquire()
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try:
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self._flag.acquire(False)
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self._flag.release()
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self._cond.notify_all()
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finally:
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self._cond.release()
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def clear(self):
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self._cond.acquire()
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try:
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self._flag.acquire(False)
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finally:
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self._cond.release()
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def wait(self, timeout=None):
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self._cond.acquire()
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try:
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if self._flag.acquire(False):
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self._flag.release()
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else:
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self._cond.wait(timeout)
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if self._flag.acquire(False):
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self._flag.release()
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return True
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return False
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finally:
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self._cond.release()
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if sys.platform != 'win32':
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#
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# Protection against unlinked semaphores if the program ends abnormally
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# and forking has been disabled.
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#
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def _cleanup_semaphore_if_leaked(name):
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name = name.encode('ascii') + bytes('\0', 'ascii')
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if len(name) > 512:
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# posix guarantees that writes to a pipe of less than PIPE_BUF
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# bytes are atomic, and that PIPE_BUF >= 512
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raise ValueError('name too long')
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fd = _get_unlinkfd()
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bits = os.write(fd, name)
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assert bits == len(name)
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def _get_unlinkfd():
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cp = current_process()
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if cp._unlinkfd is None:
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r, w = os.pipe()
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pid = os.fork()
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if pid == 0:
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try:
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from setproctitle import setproctitle
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setproctitle("[sem_cleanup for %r]" % cp.pid)
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except:
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pass
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# Fork a process which will survive until all other processes
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# which have a copy of the write end of the pipe have exited.
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# The forked process just collects names of semaphores until
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# EOF is indicated. Then it tries unlinking all the names it
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# has collected.
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_collect_names_then_unlink(r)
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os._exit(0)
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os.close(r)
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cp._unlinkfd = w
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return cp._unlinkfd
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def _collect_names_then_unlink(r):
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# protect the process from ^C and "killall python" etc
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signal.signal(signal.SIGINT, signal.SIG_IGN)
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signal.signal(signal.SIGTERM, signal.SIG_IGN)
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# close all fds except r
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try:
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MAXFD = os.sysconf("SC_OPEN_MAX")
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except:
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MAXFD = 256
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closerange(0, r)
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closerange(r + 1, MAXFD)
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# collect data written to pipe
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data = []
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while 1:
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try:
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s = os.read(r, 512)
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except:
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# XXX IO lock might be held at fork, so don't try
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# printing unexpected exception - see issue 6721
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pass
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else:
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if not s:
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break
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data.append(s)
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# attempt to unlink each collected name
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for name in bytes('', 'ascii').join(data).split(bytes('\0', 'ascii')):
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try:
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sem_unlink(name.decode('ascii'))
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except:
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# XXX IO lock might be held at fork, so don't try
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# printing unexpected exception - see issue 6721
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pass
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