flatMapCompletable does not call the given Action

Question

I was expecting flatMapCompletable will call the given Action when Completable completes normally. However, it does not work as I thought. Here's a simple example:

    PublishProcessor<String> processor = PublishProcessor.create();

    processor.flatMapCompletable(s2 -> {
        System.out.println("s2 " + s2);
        return Completable.complete();
    }).subscribe(() -> {
        System.out.println("done"); // it does not come here
    });

Is this expected behavior? If so, How can I check if Completable task is finished? Completable.complete().doFinally()?

Answer 1

You need to call processor.onComplete(); in order to get Action onComplete. This is because you are still subscribed to subject while it listens for incoming events.

Flowable completes normally

    Flowable.just(1).flatMapCompletable(s2 -> {
        System.out.println("s2 " + s2);
        return Completable.complete();
    }).subscribe(() -> {
        System.out.println("done"); // it does come here
    });

Answer 2

As Alexander pointed out, the reason why you don't get anything is PublishProcessor never completes.

JavaDoc of flatmapCompletable notes as below.

Maps each element of the upstream Observable into CompletableSources, subscribes to them and waits until the upstream and all CompletableSources complete.

So you have to make sure the upstream Observable and all of the CompletableSources complete to receive any events.

Thanks.