code: def echo_node_alarm_callback(self, block_number):
          
          if not self.ready.is_set():
              self.ready.set()
          log.debug('echo_node callback', block_number=block_number)
          if self.stop_signal is not None:
              return REMOVE_CALLBACK
          else:
              self.greenlets.add(gevent.spawn(self.poll_all_received_events))
              return True
docs: This can be registered with the raiden AlarmTask.
          If `EchoNode.stop()` is called, it will give the return signal to be removed from
          the AlarmTask callbacks.