Why “Maybe.doOnDispose” is not supported in RxJava2?

Question

I'm using Maybe class in RxJava2.

I registered the doOnDispose callback to detect the Dispose event, but it is not fired.

Maybe.just("aaa")
    .doOnDispose({ /* do something */ })
    .subscribe( ... )

I looked at the RxJava 2 code, but Maybe seemed not to support doOnDispose .

Maybe is create MaybePeek (not DoOnDisposeObserver ) object in doOnDispose ,,,

@CheckReturnValue
@SchedulerSupport("none")
public final Maybe<T> doOnDispose(Action onDispose) {
    return RxJavaPlugins.onAssembly(new MaybePeek(this, Functions.emptyConsumer(), Functions.emptyConsumer(), Functions.emptyConsumer(), Functions.EMPTY_ACTION, Functions.EMPTY_ACTION, (Action)ObjectHelper.requireNonNull(onDispose, "onDispose is null")));
}

protected void subscribeActual(MaybeObserver<? super T> observer) {
    this.source.subscribe(new MaybePeek.MaybePeekObserver(observer, this));
}

But, Single is create DoOnDisposeObserver , and it is worked fine.

@CheckReturnValue
@SchedulerSupport("none")
public final Single<T> doOnDispose(Action onDispose) {
    ObjectHelper.requireNonNull(onDispose, "onDispose is null");
    return RxJavaPlugins.onAssembly(new SingleDoOnDispose(this, onDispose));
}

protected void subscribeActual(SingleObserver<? super T> s) {
    this.source.subscribe(new SingleDoOnDispose.DoOnDisposeObserver(s, this.onDispose));
}

Why Maybe.doOnDispose is not supported?

Answer 1

As the documentation says about doOnDispose(Action onDispose)

Calls the dispose Action if the downstream disposes the sequence.

Since your downstream never dispose it, it will never call.

Disposable disposable = Maybe.just("aaa")
    .doOnDispose({ /* do something */ })
    .subscribe( ... )

disposable.dispose();

Now the action in doOnDispose should be called.

Note that if the completion of the stream takes less time than the going to the next operation ( disposable.dispose() ), then the onDispose action should not be called. So, in order to verify it you can use a delay:

Disposable disposable = Maybe.just("aaa")
    .delay(2000, TimeUnit.MILLISECONDS)
    .doOnDispose({ /* do something */ })
    .subscribe( ... )

disposable.dispose();

Now the action should be fired.