code: func (mux *TypeMux) Stop() {
  	mux.mutex.Lock()
  	for _, subs := range mux.subm {
  		for _, sub := range subs {
  			sub.closewait()
  		}
  	}
  	mux.subm = nil
  	mux.stopped = true
  	mux.mutex.Unlock()
  }
docs: // Stop closes a mux. The mux can no longer be used.
  // Future Post calls will fail with ErrMuxClosed.
  // Stop blocks until all current deliveries have finished.