Monitor for unobserved errors

[stefanrusek]

This defers the actual finalization handling to a secondary class.
Additionally if any of the continuations immediately observe the error,
then no additional finalization logic is performed.

Fixes #48

[richardjrossiii]

I like the concept, and it seems like a fairly portable API to have everywhere. My one concern, however, is that finalize() is not guaranteed to be called on a user-controlled thread (in fact, on the desktop JVM, all finalizers are run on a dedicated thread), which makes the uncaught exception handler bit somewhat useless.

[stefanrusek]

@richardjrossiii The fact that it runs on a GC thread doesn't make it useless. It might prevent that handler from directly calling UI methods, but it could still log the error someplace useful. Also the default handler could fire off a new Task to deal with the error like so:

final Executor myUIExecutor = ...;
Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
    public void uncaughtException(Thread t, final Throwable e) {
        Task.Call(new Callable<Void>() {
            // anything you want to do..
        }, myUIExecutor);
    }
});

[grantland]

This looks interesting! I want to play around with this to see how this plays out in different environments.

If it works well, we'd also want this configurable and off by default to not be a breaking change and so developers can turn it off in production environments.

[stefanrusek]

To turn it off by default, we could just add a static field and getUnobservedExceptionHandler() and setUnobservedExceptionHandler() methods. the default would just eat the exception. Then use that instead of Thread.getDefaultUncaughExceptionHandler().

[facebook-github-bot]

@stefanrusek updated the pull request.

[stefanrusek]

@grantland I made it configurable and added a test.

[grantland]

FYI, I'll be without a computer until December and won't be able to take a look at this until then. Hope that's ok and sorry!

[stefanrusek]

@grantland ping

[grantland]

Finally got around to playing around with it and it's awesome! Thanks for updating it so that it doesn't throw on the uncaught exception handler by default.

@hallucinogen mind taking a look at the API and giving a second opinion?

[grantland]

one small edit: we should be using try { ... } finally { super.finalize() } here

[facebook-github-bot]

@stefanrusek updated the pull request.

[grantland]

we probably want to make this package private

[hallucinogen]

+1

[hallucinogen]

oh right. In Java isn't this usually in some form of onUnobservedException

[grantland]

This currently matches Thread.UncaughtExceptionHandler's pattern: https://developer.android.com/reference/java/lang/Thread.UncaughtExceptionHandler.html

[hallucinogen]

lgtm then

[grantland]

Last nit is to hide UnobservedErrorNotifier

[facebook-github-bot]

@stefanrusek updated the pull request.

[stefanrusek]

@grantland updated visibility

[grantland]

Thanks for you're awesome contribution! As a thank you, wed like to send you some Parse swag. If you're interested, send me your mailing address and t-shirt size to my email address on my profile page.