def process_callback(self, block=True):
try:<EOL><INDENT>(callback, args) = self._queue.get(block=block)<EOL>try:<EOL><INDENT>callback(*args)<EOL><DEDENT>finally:<EOL><INDENT>self._queue.task_done()<EOL><DEDENT><DEDENT>except queue.Empty:<EOL><INDENT>return False<EOL><DEDENT>return True<EOL>
Dispatch a single callback in the current thread.

        :param boolean block: If True, blocks waiting for a callback to come.
        :return: True if a callback was processed; otherwise False.