RxJava's retryWhen operator

I'm trying to understand retryWhen operator in depth and I have some code as below.

    Flowable.just(1, 2, 3, 4, 5)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .retryWhen { throwable ->
                Log.d("Debug", "retryWhen proceed...")
                throw Exception("There is a exception")
            }
            .subscribe(
                    { item ->
                        Log.d("Debug", "success : $item")
                    },
                    { throwable ->
                        Log.d("Debug", "error : ${throwable.message}")
                    },
                    {
                        Log.d("Debug", "complete")
                    }
            )

And the result is shwon as below.

Debug: retryWhen proceed...

Debug: error : There is a exception

The question is that when retryWhen operator is triggered?

I assume retryWhen operator will be triggered only when there is a exception occurs.

But the result is not what I thought obviously,

Any thoughts on this? Thanks!

retryWhen { errors -> ... } take an Observable<Throwable> and should return an Observable that return anything for retrying or an error for stop retrying.

One example could be:

.retryWhen(attempts -> {
  return attempts.zipWith(Observable.range(1, 3), (n, i) -> i).flatMap(i -> {
    System.out.println("delay retry by " + i + " second(s)");
    return Observable.timer(i, TimeUnit.SECONDS);
  });
})

(taken from http://reactivex.io/documentation/operators/retry.html)
This code will delay each retry.

By the way, throwing an exception is not the thing to do in this method.

Documentation:
* Great blog article that explained the retryWhen