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# Module implementing synchronization primitives

# multiprocessing/synchronize.py

# 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

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 locked(self):

return self._semlock._is_zero()

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):

'''Returns current value of Semaphore.

Raises NotImplementedError on Mac OSX

because of broken sem_getvalue().

'''

return self._semlock._get_value()

def __repr__(self):

try:

value = self.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.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.get_value() -

self._woken_count.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):

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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