code: func (q *TransmitLimitedQueue) lazyInit() {
  	if q.tq == nil {
  		q.tq = btree.New(32)
  	}
  	if q.tm == nil {
  		q.tm = make(map[string]*limitedBroadcast)
  	}
  }
docs: // lazyInit initializes internal data structures the first time they are
  // needed.  You must already hold the mutex.