2.x: parallel blocks forever with TestScheduler

io.reactivex.rxjava2:rxjava:2.2.3

public class DemoApplication {
   public static void main(String[] args) {
       List<Map.Entry<Integer, String>> entries = Arrays.asList(
               new AbstractMap.SimpleImmutableEntry<>(3, "hello"),
               new AbstractMap.SimpleImmutableEntry<>(3, "world")
       );

       Flowable.fromIterable(entries)
               .flatMap(entry -> Flowable.range(1, entry.getKey())
                       .parallel()
                       .runOn(Schedulers.io())
                       .flatMap(i -> logIt(entry.getValue()).toFlowable())
                       .sequential()
               )
               .all(success -> success)
               .doOnSuccess(success -> System.out.println("good"))
               .doOnError(Throwable::printStackTrace)
               .blockingGet();
   }

   private static Single<Boolean> logIt(String s) {
       System.out.println(s);

       return Single.just(true);
   }
}

This code works as expected. However, replacing Schedulers.io() with TestScheduler blocks forever. Gradle project attached.

demo.zip

[akarnokd]

even if there’s no delay or interval in the code […] That wouldn’t be my first thought

TestScheduler captures tasks scheduled by operators so that side-effects can be performed before the task then gets executed on demand via advanceTimeBy, even if they are logically not delayed. In reality, there is always some non-zero time elapsing between the scheduling and execution of such task. TestScheduler just makes it deterministic.

if you do that here, I’ll be happy to send a PR for the docs.

If you wish to contribute, you could extend its JavaDocs with the explicit mention of advanceTimeBy or even a short example.

[asarkar]

@akarnokd https://github.com/ReactiveX/RxJava/pull/6356