code: func (ctl *HandshakeController) releaseKeyNoLock(symkeyid string, topic *Topic) bool {
  	if ctl.symKeyIndex[symkeyid] == nil {
  		log.Debug("no symkey", "symkeyid", symkeyid)
  		return false
  	}
  	ctl.symKeyIndex[symkeyid].expiredAt = time.Now()
  	log.Debug("handshake release", "symkeyid", symkeyid)
  	return true
  }
docs: // Expire a symmetric key, making it eligible for garbage collection