The main loop for the flow processing request queue.

def _FlowProcessingRequestHandlerLoop(self, handler):
    """The main loop for the flow processing request queue."""
    while not self.flow_processing_request_handler_stop:
      try:
        msgs = self._LeaseFlowProcessingReqests()
        if msgs:
          for m in msgs:
            self.flow_processing_request_handler_pool.AddTask(
                target=handler, args=(m,))
        else:
          time.sleep(self._FLOW_REQUEST_POLL_TIME_SECS)

      except Exception as e:  # pylint: disable=broad-except
        logging.exception("_FlowProcessingRequestHandlerLoop raised %s.", e)
        break