zip: doOnTerminate is not called on some observables

    @Test
    public void test() {
        Observable.zip(
                Observable.just("1")
                        .doOnTerminate(() -> System.out.println("TERMINATE 1")),
                Observable.just("2")
                        .delay(1, TimeUnit.SECONDS)
                        .doOnTerminate(() -> System.out.println("TERMINATE 2")),
                (result1, result2) -> null)
                .doOnTerminate(() -> System.out.println("TERMINATE"))
                .toBlocking()
                .single();
    }

Output:

TERMINATE 1
TERMINATE

Expected output:

TERMINATE 1
TERMINATE 2
TERMINATE

Or maybe my thinking is wrong?

Context of the problem: I use Hystrix observable commands in zip:

Observable.zip(
  new MyHystrixObservableCommand(arg1).toObservable(),
  new MyHystrixObservableCommand(arg2).toObservable(),
  (result1, result2) -> null)
.toBlocking()
.single()

and hystrix command semaphore release happens in doOnTerminate. One of them is not called and semaphore is not released.

[akarnokd]

With collections over time, you can’t know you are just before completion. The zip operator behaves correctly and you need a different operator, doOnTerminate+doOnUnsubscribe or using, to handle completion and unsubscription case together.

[abersnaze]

DoOnTerminate won’t be called if the observable is unsubscribed before the onCompleted/onError. Use doOnUnsubscribe if you need to always get a call back.