code: func (ln *Listener) Close() error {
  	ln.mu.Lock()
  	defer ln.mu.Unlock()
  
  	if ln.closed {
  		return errListenerClosed
  	}
  	ln.closed = true
  	close(ln.exit)
  
  	return ln._closeTheCn(errListenerClosed)
  }
docs: // Close closes the listener, releasing any open resources.