#
# Module implementing synchronization primitives
#
# multiprocessing/synchronize.py
#
# Copyright (c) 2006-2008, R Oudkerk
# Licensed to PSF under a Contributor Agreement.
#
__all__ = [
'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition', 'Event'
]
import threading
import sys
import tempfile
import _multiprocessing
import time
from . import context
from . import process
from . import util
# TODO: Do any platforms still lack a functioning sem_open?
try:
from _multiprocessing import SemLock, sem_unlink
except ImportError:
raise ImportError("This platform lacks a functioning sem_open" +
" implementation. https://github.com/python/cpython/issues/48020.")
#
# Constants
#
# These match the enum in Modules/_multiprocessing/semaphore.c
RECURSIVE_MUTEX = 0
SEMAPHORE = 1
SEM_VALUE_MAX = _multiprocessing.SemLock.SEM_VALUE_MAX
#
# Base class for semaphores and mutexes; wraps `_multiprocessing.SemLock`
#
class SemLock(object):
_rand = tempfile._RandomNameSequence()
def __init__(self, kind, value, maxvalue, *, ctx):
if ctx is None:
ctx = context._default_context.get_context()
self._is_fork_ctx = ctx.get_start_method() == 'fork'
unlink_now = sys.platform == 'win32' or self._is_fork_ctx
for i in range(100):
try:
sl = self._semlock = _multiprocessing.SemLock(
kind, value, maxvalue, self._make_name(),
unlink_now)
except FileExistsError:
pass
else:
break
else:
raise FileExistsError('cannot find name for semaphore')
util.debug('created semlock with handle %s' % sl.handle)
self._make_methods()
if sys.platform != 'win32':
def _after_fork(obj):
obj._semlock._after_fork()
util.register_after_fork(self, _after_fork)
if self._semlock.name is not None:
# We only get here if we are on Unix with forking
# disabled. When the object is garbage collected or the
# process shuts down we unlink the semaphore name
from .resource_tracker import register
register(self._semlock.name, "semaphore")
util.Finalize(self, SemLock._cleanup, (self._semlock.name,),
exitpriority=0)
@staticmethod
def _cleanup(name):
from .resource_tracker import unregister
sem_unlink(name)
unregister(name, "semaphore")
def _make_methods(self):
self.acquire = self._semlock.acquire
self.release = self._semlock.release
def __enter__(self):
return self._semlock.__enter__()
def __exit__(self, *args):
return self._semlock.__exit__(*args)
def __getstate__(self):
context.assert_spawning(self)
sl = self._semlock
if sys.platform == 'win32':
h = context.get_spawning_popen().duplicate_for_child(sl.handle)
else:
if self._is_fork_ctx:
raise RuntimeError('A SemLock created in a fork context is being '
'shared with a process in a spawn context. This is '
'not supported. Please use the same context to create '
'multiprocessing objects and Process.')
h = sl.handle
return (h, sl.kind, sl.maxvalue, sl.name)
def __setstate__(self, state):
self._semlock = _multiprocessing.SemLock._rebuild(*state)
util.debug('recreated blocker with handle %r' % state[0])
self._make_methods()
# Ensure that deserialized SemLock can be serialized again (gh-108520).
self._is_fork_ctx = False
@staticmethod
def _make_name():
return '%s-%s' % (process.current_process()._config['semprefix'],
next(SemLock._rand))
#
# Semaphore
#
class Semaphore(SemLock):
def __init__(self, value=1, *, ctx):
SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX, ctx=ctx)
def get_value(self):
return self._semlock._get_value()
def __repr__(self):
try:
value = self._semlock._get_value()
except Exception:
value = 'unknown'
return '<%s(value=%s)>' % (self.__class__.__name__, value)
#
# Bounded semaphore
#
class BoundedSemaphore(Semaphore):
def __init__(self, value=1, *, ctx):
SemLock.__init__(self, SEMAPHORE, value, value, ctx=ctx)
def __repr__(self):
try:
value = self._semlock._get_value()
except Exception:
value = 'unknown'
return '<%s(value=%s, maxvalue=%s)>' % \
(self.__class__.__name__, value, self._semlock.maxvalue)
#
# Non-recursive lock
#
class Lock(SemLock):
def __init__(self, *, ctx):
SemLock.__init__(self, SEMAPHORE, 1, 1, ctx=ctx)
def __repr__(self):
try:
if self._semlock._is_mine():
name = process.current_process().name
if threading.current_thread().name != 'MainThread':
name += '|' + threading.current_thread().name
elif not self._semlock._is_zero():
name = 'None'
elif self._semlock._count() > 0:
name = 'SomeOtherThread'
else:
name = 'SomeOtherProcess'
except Exception:
name = 'unknown'
return '<%s(owner=%s)>' % (self.__class__.__name__, name)
#
# Recursive lock
#
class RLock(SemLock):
def __init__(self, *, ctx):
SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1, ctx=ctx)
def __repr__(self):
try:
if self._semlock._is_mine():
name = process.current_process().name
if threading.current_thread().name != 'MainThread':
name += '|' + threading.current_thread().name
count = self._semlock._count()
elif not self._semlock._is_zero():
name, count = 'None', 0
elif self._semlock._count() > 0:
name, count = 'SomeOtherThread', 'nonzero'
else:
name, count = 'SomeOtherProcess', 'nonzero'
except Exception:
name, count = 'unknown', 'unknown'
return '<%s(%s, %s)>' % (self.__class__.__name__, name, count)
#
# Condition variable
#
class Condition(object):
def __init__(self, lock=None, *, ctx):
self._lock = lock or ctx.RLock()
self._sleeping_count = ctx.Semaphore(0)
self._woken_count = ctx.Semaphore(0)
self._wait_semaphore = ctx.Semaphore(0)
self._make_methods()
def __getstate__(self):
context.assert_spawning(self)
return (self._lock, self._sleeping_count,
self._woken_count, self._wait_semaphore)
def __setstate__(self, state):
(self._lock, self._sleeping_count,
self._woken_count, self._wait_semaphore) = state
self._make_methods()
def __enter__(self):
return self._lock.__enter__()
def __exit__(self, *args):
return self._lock.__exit__(*args)
def _make_methods(self):
self.acquire = self._lock.acquire
self.release = self._lock.release
def __repr__(self):
try:
num_waiters = (self._sleeping_count._semlock._get_value() -
self._woken_count._semlock._get_value())
except Exception:
num_waiters = 'unknown'
return '<%s(%s, %s)>' % (self.__class__.__name__, self._lock, num_waiters)
def wait(self, timeout=None):
assert self._lock._semlock._is_mine(), \
'must acquire() condition before using wait()'
# indicate that this thread is going to sleep
self._sleeping_count.release()
# release lock
count = self._lock._semlock._count()
for i in range(count):
self._lock.release()
try:
# wait for notification or timeout
return self._wait_semaphore.acquire(True, timeout)
finally:
# indicate that this thread has woken
self._woken_count.release()
# reacquire lock
for i in range(count):
self._lock.acquire()
def notify(self, n=1):
assert self._lock._semlock._is_mine(), 'lock is not owned'
assert not self._wait_semaphore.acquire(
False), ('notify: Should not have been able to acquire '
+ '_wait_semaphore')
# to take account of timeouts since last notify*() we subtract
# woken_count from sleeping_count and rezero woken_count
while self._woken_count.acquire(False):
res = self._sleeping_count.acquire(False)
assert res, ('notify: Bug in sleeping_count.acquire'
+ '- res should not be False')
sleepers = 0
while sleepers < n and self._sleeping_count.acquire(False):
self._wait_semaphore.release() # wake up one sleeper
sleepers += 1
if sleepers:
for i in range(sleepers):
self._woken_count.acquire() # wait for a sleeper to wake
# rezero wait_semaphore in case some timeouts just happened
while self._wait_semaphore.acquire(False):
pass
def notify_all(self):
self.notify(n=sys.maxsize)
def wait_for(self, predicate, timeout=None):
result = predicate()
if result:
return result
if timeout is not None:
endtime = time.monotonic() + timeout
else:
endtime = None
waittime = None
while not result:
if endtime is not None:
waittime = endtime - time.monotonic()
if waittime <= 0:
break
self.wait(waittime)
result = predicate()
return result
#
# Event
#
class Event(object):
def __init__(self, *, ctx):
self._cond = ctx.Condition(ctx.Lock())
self._flag = ctx.Semaphore(0)
def is_set(self):
with self._cond:
if self._flag.acquire(False):
self._flag.release()
return True
return False
def set(self):
with self._cond:
self._flag.acquire(False)
self._flag.release()
self._cond.notify_all()
def clear(self):
with self._cond:
self._flag.acquire(False)
def wait(self, timeout=None):
with self._cond:
if self._flag.acquire(False):
self._flag.release()
else:
self._cond.wait(timeout)
if self._flag.acquire(False):
self._flag.release()
return True
return False
def __repr__(self) -> str:
set_status = 'set' if self.is_set() else 'unset'
return f"<{type(self).__qualname__} at {id(self):#x} {set_status}>"
#
# Barrier
#
class Barrier(threading.Barrier):
def __init__(self, parties, action=None, timeout=None, *, ctx):
import struct
from .heap import BufferWrapper
wrapper = BufferWrapper(struct.calcsize('i') * 2)
cond = ctx.Condition()
self.__setstate__((parties, action, timeout, cond, wrapper))
self._state = 0
self._count = 0
def __setstate__(self, state):
(self._parties, self._action, self._timeout,
self._cond, self._wrapper) = state
self._array = self._wrapper.create_memoryview().cast('i')
def __getstate__(self):
return (self._parties, self._action, self._timeout,
self._cond, self._wrapper)
@property
def _state(self):
return self._array[0]
@_state.setter
def _state(self, value):
self._array[0] = value
@property
def _count(self):
return self._array[1]
@_count.setter
def _count(self, value):
self._array[1] = value
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