code: def requeue(self, time_ms=0, backoff=True):
          
          if self._has_responded:
              raise NSQException('already responded')
          self._has_responded = True
          self.on_requeue.send(self, timeout=time_ms, backoff=backoff)
docs: Respond to nsqd that you’ve failed to process this message successfully
          (and would like it to be requeued).