Unhandled errors go to UncaughtExceptionHandler

[loganj]

Rather than swallowing/logging errors, ScheduledAction now delivers them
to the UncaughtExceptionHandler for the executing Thread. This gives
client applications control over the handling of errors that occur off
of the calling Thread.

[benjchristensen]

Thank you @loganj

[loganj]

Oops, forgot to reference the original issue: #1682

[benjchristensen]

I haven't had a chance to test yet, but without printStackTrace will this silently fail unless someone has registered a default handler, or does the JVM have a default one?

[loganj]

Pretty sure ThreadGroup has us covered.

If this thread group has a parent thread group, the uncaughtException method of that parent is called with the same two arguments.

Otherwise, this method checks to see if there is a default uncaught exception handler installed, and if so, its uncaughtException method is called with the same two arguments.

Otherwise, this method determines if the Throwable argument is an instance of ThreadDeath. If so, nothing special is done. Otherwise, a message containing the thread's name, as returned from the thread's getName method, and a stack backtrace, using the Throwable's printStackTrace method, is printed to the standard error stream.

[benjchristensen]

Ah nice. That's exactly what I'd want it to do. I'll play to confirm.

Thanks @loganj for helping out with this.

[benjchristensen]

Confirmed. It works perfectly.

    public static void main(String[] args) throws Exception {

        Observable.interval(100, TimeUnit.MILLISECONDS).map(i -> {
            throw new RuntimeException("fail!");
        }).subscribe();

        Thread.sleep(100000);
    }

outputs to terminal

Exception in thread "RxComputationThreadPool-1" java.lang.IllegalStateException: Exception thrown on Scheduler.Worker thread. Add `onError` handling.
    at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:50)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: rx.exceptions.OnErrorNotImplementedException: fail!
    at rx.Observable$36.onError(Observable.java:7390)
    at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:127)
    at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:96)
    at rx.internal.operators.OperatorMap$1.onError(OperatorMap.java:48)
    at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:56)
    at rx.internal.operators.OnSubscribeTimerPeriodically$1.call(OnSubscribeTimerPeriodically.java:51)
    at rx.Scheduler$Worker$1.call(Scheduler.java:118)
    at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:45)
    ... 7 more
Caused by: java.lang.RuntimeException: fail!
    at ErrorsTest.lambda$0(ErrorsTest.java:10)
    at ErrorsTest$$Lambda$1/1406718218.call(Unknown Source)
    at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:54)
    ... 10 more
Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: Long.class
    at rx.exceptions.OnErrorThrowable.addValueAsLastCause(OnErrorThrowable.java:98)
    at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:56)
    ... 10 more