code: func (h *Handle) NewSessionStatsCollector() *SessionStatsCollector {
  	h.listHead.Lock()
  	defer h.listHead.Unlock()
  	newCollector := &SessionStatsCollector{
  		mapper:  make(tableDeltaMap),
  		rateMap: make(errorRateDeltaMap),
  		next:    h.listHead.next,
  	}
  	h.listHead.next = newCollector
  	return newCollector
  }
docs: // NewSessionStatsCollector allocates a stats collector for a session.