Leases a number of message handler requests up to the indicated limit.

def RegisterMessageHandler(self, handler, lease_time, limit=1000):
    """Leases a number of message handler requests up to the indicated limit."""
    self.UnregisterMessageHandler()

    self.handler_stop = False
    self.handler_thread = threading.Thread(
        name="message_handler",
        target=self._MessageHandlerLoop,
        args=(handler, lease_time, limit))
    self.handler_thread.daemon = True
    self.handler_thread.start()