code: func (pot *partitionOffsetTracker) commit(committer offsetCommitter) error {
  	pot.l.Lock()
  	defer pot.l.Unlock()
  
  	if pot.highestProcessedOffset > pot.lastCommittedOffset {
  		if err := committer(pot.highestProcessedOffset); err != nil {
  			return err
  		}
  		pot.lastCommittedOffset = pot.highestProcessedOffset
  		return nil
  	} else {
  		return nil
  	}
  }
docs: // Commit calls a committer function if the highest processed offset is out
  // of sync with the last committed offset.