code: func (m *SubscriptionManager) notifySubscriber(sub *newSubscription,
  	block BlockNtfn) {
  
  	select {
  	case sub.ntfnQueue.ChanIn() <- block:
  	case <-sub.quit:
  	case <-m.quit:
  		return
  	}
  }
docs: // notifySubscriber notifies a single subscriber about the block.