def release(self):
        """release one ownership of the lock

        if the calling greenlet has :meth:`acquired <acquire>` the lock more
        than once this will simply decrement the counter. if this is a final
        release then a waiting greenlet is awoken

        :raises:
            `RuntimeError` if the calling greenlet is not the lock's owner
        """
        if not self._locked or self._owner is not compat.getcurrent():
            raise RuntimeError("cannot release un-acquired lock")
        self._count -= 1
        if self._count == 0:
            self._owner = None
            if self._waiters:
                waiter = self._waiters.popleft()
                self._locked = True
                self._owner = waiter
                scheduler.state.awoken_from_events.add(waiter)
            else:
                self._locked = False
                self._owner = None
release one ownership of the lock

        if the calling greenlet has :meth:`acquired <acquire>` the lock more
        than once this will simply decrement the counter. if this is a final
        release then a waiting greenlet is awoken

        :raises:
            `RuntimeError` if the calling greenlet is not the lock's owner