busMessage() silently catches exceptions

[piegamesde]

I spent the last half hour tracking down why my code wasn't executed to find out the the busMessage() callback silently caught my NullPointerException. Other callbacks are probably affected too.

[neilcsmith-net]

Can you give me a bit more of a clue about your code that was failing and where?

[piegamesde]

I did

bus.connect(new Bus.MESSAGE() {
	@Override
	public void busMessage(Bus bus, Message message) {
	}
});

Inside the busMessage a RuntimeException was thrown. The method caller caught it silently without dumping a stack trace.

[neilcsmith-net]

OK, thanks. Quick look suggests these are called on the executor service, so this is kind of expected behaviour. May need to consider a better approach, although only if we can do it without impacting performance of correctly functioning code.

[neilcsmith-net]

Consider ability to add exception handler for executor service.

[MaZderMind]

The straight forward way would be to wrap bus.dispatchMessage(msg); in GstBusAPI.BusSyncHandler#callback with a try-catch and log the exception there.

This would solve the Problem of the Exception being invisible (which did bite me more then once, too) while not adding any burden on correctly functioning code.

[MaZderMind]

As a side note: Catching Exceptions within the Runnable seems to be good practice anyway: https://stackoverflow.com/a/24902026/1659732

[neilcsmith-net]

Yes, potentially we could add something in https://github.com/gstreamer-java/gst1-java-core/blob/master/src/org/freedesktop/gstreamer/Bus.java#L733

Although I'm more inclined to an uncaught exception handler in https://github.com/gstreamer-java/gst1-java-core/blob/master/src/org/freedesktop/gstreamer/Gst.java#L654 (and removing the applet check!)

Catching Exception is not enough - we also need to be reporting at least UnsatisfiedLinkError.

[neilcsmith-net]

OK, the uncaught exception handler approach doesn't work due to the architecture of the executor anyway. So, catching and logging Throwable at https://github.com/gstreamer-java/gst1-java-core/blob/master/src/org/freedesktop/gstreamer/Bus.java#L838 This is per message handler, so other handlers will still receive the message, which seems the right approach.