Exceptions thrown in several threads simultaneously cause the application to crash when using ParallelFlowable

In Android application I’m trying to perform a simple parallel task using ParallelFlowable from RxJava 2.0.6.

public void doParallelAsyncJob() {
    subscription = Flowable
            .fromArray("1", "2", "3", "4", "5", "6", "7", "8")
            .parallel()
            .runOn(Schedulers.computation())
            .map(Integer::parseInt)
            .sequential()
            .toList()
            .subscribeOn(Schedulers.computation())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(
                    result -> showSuccessDialog(),
                    error -> showErrorDialog()
            );
}

As you can see, the code takes several strings and tries to parse them as integers. In this case all numbers are processed successfully, so the success dialog is shown. If I use the following sequence:

.fromArray("wrong", "2", "3", "4", "5", "6", "7", "8")

Then the error dialog appears, because one of the items cannot be parsed as number. This is a correct behavior. However, if I add two incorrect items instead of one:

.fromArray("wrong", "wrong", "3", "4", "5", "6", "7", "8")

Then the application just crashes. It seems to me that the reason is because the exception happened in two threads at once, but I may be wrong in the conclusion.

When I implement the parallelization the old way, the application doesn’t crash:

public void doParallelAsyncJobOldWay() {
    subscription = Flowable
            .fromArray("wrong", "wrong", "3", "4", "5", "6", "7", "8")
            .flatMap(number ->
                    Flowable
                            .just(Integer.parseInt(number))
                            .subscribeOn(Schedulers.computation())
            )
            .toList()
            .subscribeOn(Schedulers.computation())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(
                    result -> showSuccessDialog(),
                    error -> showErrorDialog()
            );
}

[romanzes]

@akarnokd Nice explanation, thanks! I tried using DisposableSubscriber for cancelling the “whole setup” and it seems to be working well.

[akarnokd]

Thanks for reporting. There is a fix waiting for review/feedback about the same issue: #5117 (reported in #5108).

As for the doParallelAsyncJobOldWay, it doesn’t crash the app but also doesn’t process “3” … “8” because Integer.parseInt crashes the function of the flatMap before it could create an async source for the rest of the input numbers.