2.x Observable.combineLatestDelayError delivers Error after completion

Observable.combineLatestDelayError sends error event after complete event happened and treated as unhandled. Checked on rx.Observable, io.reactivex.Observable and Flowable

    @Test
    public void testCombine() {
        rx.observers.TestSubscriber<Integer> testSubscriber = rx.observers.TestSubscriber.create();

        rx.Observable<Long> emptyObservable = rx.Observable.empty();
        rx.Observable<Object> errorObservable = rx.Observable.error(new Exception());

        rx.Observable.combineLatestDelayError(
                Arrays.asList(
                        emptyObservable
                                .doOnEach(integerNotification -> System.out.println("emptyObservable: " + integerNotification))
                                .doOnTerminate(() -> System.out.println("emptyObservable: doFinally")),
                        errorObservable
                                .doOnEach(integerNotification -> System.out.println("errorObservable: " + integerNotification))
                                .doOnTerminate(() -> System.out.println("errorObservable: doFinally"))),
                objects -> 0
        )
                .doOnEach(integerNotification -> System.out.println("combineLatestDelayError: " + integerNotification))
                .doOnTerminate(() -> System.out.println("combineLatestDelayError: doFinally"))
                .subscribe(testSubscriber);

        testSubscriber.awaitTerminalEvent();
    }

    @Test
    public void testCombine2() {
        TestObserver<Integer> testObserver = TestObserver.create();

        Observable<Long> emptyObservable = Observable.empty();
        Observable<Object> errorObservable = Observable.error(new Exception());

        Observable.combineLatestDelayError(
                Arrays.asList(
                        emptyObservable
                                .doOnEach(integerNotification -> System.out.println("emptyObservable: " + integerNotification))
                                .doFinally(() -> System.out.println("emptyObservable: doFinally")),
                        errorObservable
                                .doOnEach(integerNotification -> System.out.println("errorObservable: " + integerNotification))
                                .doFinally(() -> System.out.println("errorObservable: doFinally"))),
                objects -> 0
        )
                .doOnEach(integerNotification -> System.out.println("combineLatestDelayError: " + integerNotification))
                .doFinally(() -> System.out.println("combineLatestDelayError: doFinally"))
                .subscribe(testObserver);

        testObserver.awaitTerminalEvent();
    }

    @Test
    public void testCombine2Flowable() {
        TestSubscriber<Integer> testObserver = TestSubscriber.create();

        Flowable<Integer> emptyFlowable = Flowable.empty();
        Flowable<Object> errorFlowable = Flowable.error(new Exception());

        Flowable.combineLatestDelayError(
                Arrays.asList(
                        emptyFlowable
                                .doOnEach(integerNotification -> System.out.println("emptyFlowable: " + integerNotification))
                                .doFinally(() -> System.out.println("emptyFlowable: doFinally")),
                        errorFlowable
                                .doOnEach(integerNotification -> System.out.println("errorFlowable: " + integerNotification))
                                .doFinally(() -> System.out.println("errorFlowable: doFinally"))),
                objects -> 0
        )
                .doOnEach(integerNotification -> System.out.println("combineLatestDelayError: " + integerNotification))
                .doFinally(() -> System.out.println("combineLatestDelayError: doFinally"))
                .subscribe(testObserver);

        testObserver.awaitTerminalEvent();
    }

Output: testCombine

emptyObservable: [rx.Notification@2b4a2ec7 OnCompleted]
emptyObservable: doFinally
combineLatestDelayError: [rx.Notification@2b4a2ec7 OnCompleted]
combineLatestDelayError: doFinally

testCombine2

emptyObservable: OnCompleteNotification
combineLatestDelayError: OnCompleteNotification
combineLatestDelayError: doFinally
emptyObservable: doFinally
errorObservable: OnErrorNotification[java.lang.Exception]
errorObservable: doFinally
java.lang.Exception
	at com.myproject.Test.testCombine2(Test.java:298)
	// not really important Stacktrace
Exception in thread "main" java.lang.Exception
	at com.myproject.Test.testCombine2(Test.java:298)
	// repeat of not important Stacktrace

testCombine2Flowable

emptyFlowable: OnCompleteNotification
combineLatestDelayError: OnCompleteNotification
combineLatestDelayError: doFinally
emptyFlowable: doFinally

If error emitter goes first or add some timer instead of empty, then everything is ok.

Also noticed difference in events order between 1.x and 2.x. Is it correct?

[akarnokd]

Yes, it looks like the other source is not cancelled in time.

I’ve posted the fix PR as #4987 that resolves 3) and this latest case.

[akarnokd]

Yes, I’m working on the fix for 3).