code: func (b *Backend) TriggerChord(groupUUID string) (bool, error) {
  	conn := b.open()
  	defer conn.Close()
  
  	m := b.redsync.NewMutex("TriggerChordMutex")
  	if err := m.Lock(); err != nil {
  		return false, err
  	}
  	defer m.Unlock()
  
  	groupMeta, err := b.getGroupMeta(groupUUID)
  	if err != nil {
  		return false, err
  	}
  
  	// Chord has already been triggered, return false (should not trigger again)
  	if groupMeta.ChordTriggered {
  		return false, nil
  	}
  
  	// Set flag to true
  	groupMeta.ChordTriggered = true
  
  	// Update the group meta
  	encoded, err := json.Marshal(&groupMeta)
  	if err != nil {
  		return false, err
  	}
  
  	_, err = conn.Do("SET", groupUUID, encoded)
  	if err != nil {
  		return false, err
  	}
  
  	return true, b.setExpirationTime(groupUUID)
  }
docs: // TriggerChord flags chord as triggered in the backend storage to make sure
  // chord is never trigerred multiple times. Returns a boolean flag to indicate
  // whether the worker should trigger chord (true) or no if it has been triggered
  // already (false)