text: #
  # 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
  
  try:
      import _multiprocess as _multiprocessing
  except ImportError:
      import _multiprocessing
  from multiprocess.process import current_process
  from multiprocess.util import Finalize, register_after_fork, debug
  from multiprocess.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 _multiprocess import SemLock
  except (ImportError):
      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 = 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 = 'unknown'
          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 xrange(count):
              self._lock.release()
  
          try:
              # wait for notification or timeout
              self._wait_semaphore.acquire(True, timeout)
          finally:
              # indicate that this thread has woken
              self._woken_count.release()
  
              # reacquire lock
              for i in xrange(count):
                  self._lock.acquire()
  
      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 xrange(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()
  