code: func (p *Pubsub) Subscribe(ev EventBuilder, l Listener) {
  	timer := gaugeLatency(PromSubLatency)
  	defer timer()
  
  	p.subsMu.Lock()
  	count := p.subs[ev.kind].Add(ev, l)
  	p.subsMu.Unlock()
  
  	if count == 1 {
  		PromSubscriptions.Inc()
  		written := make(chan struct{}, 1)
  		p.send <- command{
  			command: ev.kind.SubCommand(),
  			channel: ev.Name(),
  			written: written,
  		}
  
  		<-written
  	}
  }
docs: // Subscribe implements Emitter.Subscribe