text: #
  # 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
  try: 
      import _multiprocess as _multiprocessing
  except ImportError:
      import _multiprocessing
  import time
  
  from . import context
  from . import process
  from . import util
  
  # 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, sem_unlink
  except ImportError:
      try:
          from _multiprocessing import SemLock, sem_unlink
      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):
  
      _rand = tempfile._RandomNameSequence()
  
      def __init__(self, kind, value, maxvalue, *, ctx):
          if ctx is None:
              ctx = context._default_context.get_context()
          name = ctx.get_start_method()
          unlink_now = sys.platform == 'win32' or name == 'fork'
          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:
              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()
  
      @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 self._semlock._get_value() == 1:
                  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 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 '<%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 = getattr(time,'monotonic',time.time)() + timeout
          else:
              endtime = None
              waittime = None
          while not result:
              if endtime is not None:
                  waittime = endtime - getattr(time,'monotonic',time.time)()
                  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
  
  #
  # 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
  