Maybe concat with firstElement still call second Maybe although the first emit value

[ekosuhariyadi]

Hi, I'm relatively new to RxJava.

I tried RxJava 2.0.6 (previously 2.0.5) to check if it still produces the same result.

Here my code (still using Java 6)

Maybe<String> m1 = Maybe.create(new MaybeOnSubscribe<String>() {

    @Override public void subscribe(MaybeEmitter<String> e) throws Exception {
        System.out.println("m1 called");
        e.onSuccess("m1");
    }
});
Maybe<String> m2 = Maybe.create(new MaybeOnSubscribe<String>() {

    @Override public void subscribe(MaybeEmitter<String> e) throws Exception {
        System.out.println("m2 called");
        e.onSuccess("m2");
    }
});
Disposable subscribe = Maybe.concat(m1, m2)
        .firstElement()
        .subscribe(new Consumer<String>() {

            @Override public void accept(String t) throws Exception {
                System.out.println(t);
            }
        });

the output :
m1 called
m1
m2 called

Is it correct or not? Because while using Observable, the second Observable is not called when the first one already emit value

Thanks

[akarnokd]

Hi and thanks for reporting. This is a bug in the underlying concat operator that doesn't expect a cancellation (happening due to firstElement) after emitting an item and happily subscribes to the next source, triggering subscription side-effects but actually cancelling out that new source immediately.

I'll post a fix shortly.

[akarnokd]

Closing via #5101.

Temporary workaround: add Maybe.empty() between the sources to absorb the extra subscription.