code: func (s tcSubs) send(tc uint64, underrun bool) {
  	for sub := range s {
  		select {
  		case <-sub.rpcSub.Err():
  			delete(s, sub)
  		case <-sub.notifier.Closed():
  			delete(s, sub)
  		default:
  			if underrun || !sub.onlyUnderrun {
  				sub.notifier.Notify(sub.rpcSub.ID, tc)
  			}
  		}
  	}
  }
docs: // send sends a changed total capacity event to the subscribers