Listen() has no stop mechanism.

[zvodd]

I ran into a problem where calling Stream.Close() causes a crash in my app.
The call was fine when the app was closing down. i.e. when other go routines being killed.
The reason, Stream.Listen() spawns a go routine with no exit feature, so it will keep polling the Stream even if it has been Closed. This of course results in a memory access violation.
I assume the reason testing hasn't picked this up before is because Steam.Close() is usually only called on exit.

I am using the following in my project to allow a stream to stop listening.
It's a slight API change adding a stop signal to Stream.Listen().
Though it might be a good idea to use the context package...

func (s *portmidi.Stream) Listen(stop <-chan int) <-chan portmidi.Event {
	const pollingInterval = 10 * time.Millisecond
	timer := time.NewTimer(pollingInterval)
	ch := make(chan portmidi.Event)
	go func(s *portmidi.Stream, ch chan portmidi.Event) {
		for {
			select {
			case <-timer.C:
				events, err := s.Read(1024)
				if err != nil {
					timer.Reset(pollingInterval)
					continue
				}
				for i := range events {
					ch <- events[i]
				}
				timer.Reset(pollingInterval)
			case <-stop:
				timer.Stop()
				return
			}
		}
	}(s, ch)
	return ch
}