code: public static <T> LatchedObserver<T> createIndexed(Action2<? super T, ? super Integer> onNext, Action1<? super Throwable> onError, CountDownLatch latch) {
          return new LatchedObserverIndexedImpl<T>(onNext, onError, Functionals.empty(), latch);
      }
docs: Create a LatchedObserver with the given indexed callback function(s) and a shared latch.