code: def commit_async(self, offsets=None, callback=None):
          
          assert self.config['api_version'] >= (0, 8, 1), 'Requires >= Kafka 0.8.1'
          assert self.config['group_id'] is not None, 'Requires group_id'
          if offsets is None:
              offsets = self._subscription.all_consumed_offsets()
          log.debug("Committing offsets: %s", offsets)
          future = self._coordinator.commit_offsets_async(
              offsets, callback=callback)
          return future
docs: Commit offsets to kafka asynchronously, optionally firing callback.
  
          This commits offsets only to Kafka. The offsets committed using this API
          will be used on the first fetch after every rebalance and also on
          startup. As such, if you need to store offsets in anything other than
          Kafka, this API should not be used. To avoid re-processing the last
          message read if a consumer is restarted, the committed offset should be
          the next message your application should consume, i.e.: last_offset + 1.
  
          This is an asynchronous call and will not block. Any errors encountered
          are either passed to the callback (if provided) or discarded.
  
          Arguments:
              offsets (dict, optional): {TopicPartition: OffsetAndMetadata} dict
                  to commit with the configured group_id. Defaults to currently
                  consumed offsets for all subscribed partitions.
              callback (callable, optional): Called as callback(offsets, response)
                  with response as either an Exception or an OffsetCommitResponse
                  struct. This callback can be used to trigger custom actions when
                  a commit request completes.
  
          Returns:
              kafka.future.Future