code: func (ms *MemoryMsgStore) Empty() error {
  	ms.Lock()
  	if ms.ageTimer != nil {
  		if ms.ageTimer.Stop() {
  			ms.wg.Done()
  		}
  		ms.ageTimer = nil
  	}
  	ms.empty()
  	ms.msgs = make(map[uint64]*pb.MsgProto)
  	ms.Unlock()
  	return nil
  }
docs: // Empty implements the MsgStore interface