RxJava 2.2.2 startsWith subscribes the subsequence streams without subscribing to the upper stream

[ykinuse]

Hi, I'm not sure if this is a bug or an expected behavior. See an example below:

        PublishSubject<Integer> subject = PublishSubject.create();
        AtomicBoolean bool = new AtomicBoolean();
        subject
                .doOnSubscribe(s->{}) << not called
                .doOnNext(s->{}) << not called
                .startWith(0)
                .switchMap(o -> Observable
                        .empty()
                        .doOnSubscribe(s -> {
                            if (!bool.get()) {
                                subject.onNext(1); << called
                            }
                        }))
                .subscribe();

Scenario: In my use case, I subscribed to a source that chained with a #startWith operator. I performed a switchMap, expecting the next value terminates it and starts a new one. Subject emits something during the switchmap. Happens on both Observable/Flowable.

Expected: receive the new event Actual: receive nothing due to subject not subscribed yet.

Have not tested on other version.

Thanks

[akarnokd]

This is a valid behavior. The PublishSubject is not subscribed at that time because startWith hasn't finished yet switching to it. Consider using BehaviorSubject.create(0) instead and not doing that reentrant onNext call.

[ykinuse]

Thanks for the clarification. PublishSubject was used as an example of some source. So I'm assuming doOnSubscribe() chained after startWith does not guaranteed subscription established to the source? Was expecting a guaranteed subscription to source before startWith emits.

[akarnokd]

No. StartWith is like concat, subscribes the next source after the previous source has completed, thus no doOnSubscribe is called on the next source until that.

[ykinuse]

Cleared my doubts. Thanks for the swift & clear response!