src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> retry(BiPredicate<? super Integer, ? super Throwable> predicate) {
        ObjectHelper.requireNonNull(predicate, "predicate is null");

        return RxJavaPlugins.onAssembly(new ObservableRetryBiPredicate<T>(this, predicate));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> retry(BiPredicate<? super Integer, ? super Throwable> predicate) {
        ObjectHelper.requireNonNull(predicate, "predicate is null");

        return RxJavaPlugins.onAssembly(new ObservableRetryBiPredicate<T>(this, predicate));
    }
Returns an Observable that mirrors the source ObservableSource, resubscribing to it if it calls {@code onError}
and the predicate returns true for that specific exception and retry count.
<p>
<img width="640" height="235" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/retry.o.ne.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code retry} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param predicate
the predicate that determines if a resubscription may happen in case of a specific exception
and retry count
@return the source ObservableSource modified with retry logic
@see #retry()
@see <a href="http://reactivex.io/documentation/operators/retry.html">ReactiveX operators documentation: Retry</a>