src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> repeatWhen(final Function<? super Observable<Object>, ? extends ObservableSource<?>> handler) {
        ObjectHelper.requireNonNull(handler, "handler is null");
        return RxJavaPlugins.onAssembly(new ObservableRepeatWhen<T>(this, handler));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> repeatWhen(final Function<? super Observable<Object>, ? extends ObservableSource<?>> handler) {
        ObjectHelper.requireNonNull(handler, "handler is null");
        return RxJavaPlugins.onAssembly(new ObservableRepeatWhen<T>(this, handler));
    }
Returns an Observable that emits the same values as the source ObservableSource with the exception of an
{@code onComplete}. An {@code onComplete} notification from the source will result in the emission of
a {@code void} item to the ObservableSource provided as an argument to the {@code notificationHandler}
function. If that ObservableSource calls {@code onComplete} or {@code onError} then {@code repeatWhen} will
call {@code onComplete} or {@code onError} on the child subscription. Otherwise, this ObservableSource will
resubscribe to the source ObservableSource.
<p>
<img width="640" height="430" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/repeatWhen.f.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code repeatWhen} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param handler
receives an ObservableSource of notifications with which a user can complete or error, aborting the repeat.
@return the source ObservableSource modified with repeat logic
@see <a href="http://reactivex.io/documentation/operators/repeat.html">ReactiveX operators documentation: Repeat</a>