PYTHON CONDITION源码阅读

这两天读了一下Python的Condition实现源码，是实现Queue的工具之一，发现是非常朴素的sleep->loop->query模式。源码很少，直接贴出，就不做注释了：）

def wait(self, timeout=None):
        """Wait until notified or until a timeout occurs.
 
        If the calling thread has not acquired the lock when this method is
        called, a RuntimeError is raised.
 
        This method releases the underlying lock, and then blocks until it is
        awakened by a notify() or notifyAll() call for the same condition
        variable in another thread, or until the optional timeout occurs. Once
        awakened or timed out, it re-acquires the lock and returns.
 
        When the timeout argument is present and not None, it should be a
        floating point number specifying a timeout for the operation in seconds
        (or fractions thereof).
 
        When the underlying lock is an RLock, it is not released using its
        release() method, since this may not actually unlock the lock when it
        was acquired multiple times recursively. Instead, an internal interface
        of the RLock class is used, which really unlocks it even when it has
        been recursively acquired several times. Another internal interface is
        then used to restore the recursion level when the lock is reacquired.
 
        """
        if not self._is_owned():
            raise RuntimeError("cannot wait on un-acquired lock")
        waiter = _allocate_lock()
        waiter.acquire()
        self.__waiters.append(waiter)
        saved_state = self._release_save()
        try:    # restore state no matter what (e.g., KeyboardInterrupt)
            if timeout is None:
                waiter.acquire()
                if __debug__:
                    self._note("%s.wait(): got it", self)
            else:
                # Balancing act:  We can't afford a pure busy loop, so we
                # have to sleep; but if we sleep the whole timeout time,
                # we'll be unresponsive.  The scheme here sleeps very
                # little at first, longer as time goes on, but never longer
                # than 20 times per second (or the timeout time remaining).
                endtime = _time() + timeout
                delay = 0.0005 # 500 us -> initial delay of 1 ms
                while True:
                    gotit = waiter.acquire(0)
                    if gotit:
                        break
                    remaining = endtime - _time()
                    if remaining <= 0:
                        break
                    delay = min(delay * 2, remaining, .05)
                    _sleep(delay)
                if not gotit:
                    if __debug__:
                        self._note("%s.wait(%s): timed out", self, timeout)
                    try:
                        self.__waiters.remove(waiter)
                    except ValueError:
                        pass
                else:
                    if __debug__:
                        self._note("%s.wait(%s): got it", self, timeout)
        finally:
            self._acquire_restore(saved_state)