code: func (p *Pss) getHandlers(topic Topic) (ret []*handler) {
  	p.handlersMu.RLock()
  	defer p.handlersMu.RUnlock()
  	for k := range p.handlers[topic] {
  		ret = append(ret, k)
  	}
  	return ret
  }
docs: // copy all registered handlers for respective topic in order to avoid data race or deadlock