code: def request_update(self):
          
          with self._lock:
              self._need_update = True
              if not self._future or self._future.is_done:
                self._future = Future()
              return self._future
docs: Flags metadata for update, return Future()
  
          Actual update must be handled separately. This method will only
          change the reported ttl()
  
          Returns:
              kafka.future.Future (value will be the cluster object after update)