cpython/Lib/multiprocessing/synchronize.py

#
# Module implementing synchronization primitives
#
# multiprocessing/synchronize.py
#
# Copyright (c) 2006-2008, R Oudkerk
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
# 3. Neither the name of author nor the names of any contributors may be
#    used to endorse or promote products derived from this software
#    without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.
#

__all__ = [
    'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Condition', 'Event'
    ]

import threading
import os
import sys

from time import time as _time, sleep as _sleep

import _multiprocessing
from multiprocessing.process import current_process
from multiprocessing.util import Finalize, register_after_fork, debug
from multiprocessing.forking import assert_spawning, Popen

# Try to import the mp.synchronize module cleanly, if it fails
# raise ImportError for platforms lacking a working sem_open implementation.
# See issue 3770
try:
    from _multiprocessing import SemLock
except (ImportError):
    raise ImportError("This platform lacks a functioning sem_open" +
                      " implementation, therefore, the required" +
                      " synchronization primitives needed will not" +
                      " function, see issue 3770.")

#
# Constants
#

RECURSIVE_MUTEX, SEMAPHORE = list(range(2))
SEM_VALUE_MAX = _multiprocessing.SemLock.SEM_VALUE_MAX

#
# Base class for semaphores and mutexes; wraps `_multiprocessing.SemLock`
#

class SemLock(object):

    def __init__(self, kind, value, maxvalue):
        sl = self._semlock = _multiprocessing.SemLock(kind, value, maxvalue)
        debug('created semlock with handle %s' % sl.handle)
        self._make_methods()

        if sys.platform != 'win32':
            def _after_fork(obj):
                obj._semlock._after_fork()
            register_after_fork(self, _after_fork)

    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):
        assert_spawning(self)
        sl = self._semlock
        return (Popen.duplicate_for_child(sl.handle), sl.kind, sl.maxvalue)

    def __setstate__(self, state):
        self._semlock = _multiprocessing.SemLock._rebuild(*state)
        debug('recreated blocker with handle %r' % state[0])
        self._make_methods()

#
# Semaphore
#

class Semaphore(SemLock):

    def __init__(self, value=1):
        SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX)

    def get_value(self):
        return self._semlock._get_value()

    def __repr__(self):
        try:
            value = self._semlock._get_value()
        except Exception:
            value = 'unknown'
        return '<Semaphore(value=%s)>' % value

#
# Bounded semaphore
#

class BoundedSemaphore(Semaphore):

    def __init__(self, value=1):
        SemLock.__init__(self, SEMAPHORE, value, value)

    def __repr__(self):
        try:
            value = self._semlock._get_value()
        except Exception:
            value = 'unknown'
        return '<BoundedSemaphore(value=%s, maxvalue=%s)>' % \
               (value, self._semlock.maxvalue)

#
# Non-recursive lock
#

class Lock(SemLock):

    def __init__(self):
        SemLock.__init__(self, SEMAPHORE, 1, 1)

    def __repr__(self):
        try:
            if self._semlock._is_mine():
                name = current_process().name
                if threading.current_thread().name != 'MainThread':
                    name += '|' + threading.current_thread().name
            elif self._semlock._get_value() == 1:
                name = 'None'
            elif self._semlock._count() > 0:
                name = 'SomeOtherThread'
            else:
                name = 'SomeOtherProcess'
        except Exception:
            name = 'unknown'
        return '<Lock(owner=%s)>' % name

#
# Recursive lock
#

class RLock(SemLock):

    def __init__(self):
        SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1)

    def __repr__(self):
        try:
            if self._semlock._is_mine():
                name = current_process().name
                if threading.current_thread().name != 'MainThread':
                    name += '|' + threading.current_thread().name
                count = self._semlock._count()
            elif self._semlock._get_value() == 1:
                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 '<RLock(%s, %s)>' % (name, count)

#
# Condition variable
#

class Condition(object):

    def __init__(self, lock=None):
        self._lock = lock or RLock()
        self._sleeping_count = Semaphore(0)
        self._woken_count = Semaphore(0)
        self._wait_semaphore = Semaphore(0)
        self._make_methods()

    def __getstate__(self):
        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 = 'unkown'
        return '<Condition(%s, %s)>' % (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
            ret = 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()
            return ret

    def notify(self):
        assert self._lock._semlock._is_mine(), 'lock is not owned'
        assert not self._wait_semaphore.acquire(False)

        # 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

        if self._sleeping_count.acquire(False): # try grabbing a sleeper
            self._wait_semaphore.release()      # wake up one sleeper
            self._woken_count.acquire()         # wait for the sleeper to wake

            # rezero _wait_semaphore in case a timeout just happened
            self._wait_semaphore.acquire(False)

    def notify_all(self):
        assert self._lock._semlock._is_mine(), 'lock is not owned'
        assert not self._wait_semaphore.acquire(False)

        # 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

        sleepers = 0
        while 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

#
# Event
#

class Event(object):

    def __init__(self):
        self._cond = Condition(Lock())
        self._flag = Semaphore(0)

    def is_set(self):
        self._cond.acquire()
        try:
            if self._flag.acquire(False):
                self._flag.release()
                return True
            return False
        finally:
            self._cond.release()

    def set(self):
        self._cond.acquire()
        try:
            self._flag.acquire(False)
            self._flag.release()
            self._cond.notify_all()
        finally:
            self._cond.release()

    def clear(self):
        self._cond.acquire()
        try:
            self._flag.acquire(False)
        finally:
            self._cond.release()

    def wait(self, timeout=None):
        self._cond.acquire()
        try:
            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
        finally:
            self._cond.release()