src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U, V> Flowable<T> timeout(Publisher<U> firstTimeoutIndicator,
            Function<? super T, ? extends Publisher<V>> itemTimeoutIndicator) {
        ObjectHelper.requireNonNull(firstTimeoutIndicator, "firstTimeoutIndicator is null");
        return timeout0(firstTimeoutIndicator, itemTimeoutIndicator, null);
    }
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U, V> Flowable<T> timeout(Publisher<U> firstTimeoutIndicator,
            Function<? super T, ? extends Publisher<V>> itemTimeoutIndicator) {
        ObjectHelper.requireNonNull(firstTimeoutIndicator, "firstTimeoutIndicator is null");
        return timeout0(firstTimeoutIndicator, itemTimeoutIndicator, null);
    }
Returns a Flowable that mirrors the source Publisher, but notifies Subscribers of a
{@code TimeoutException} if either the first item emitted by the source Publisher or any subsequent item
doesn't arrive within time windows defined by other Publishers.
<p>
<img width="640" height="400" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/timeout5.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator honors backpressure from downstream. Both this and the returned {@code Publisher}s
are expected to honor backpressure as well. If any of then violates this rule, it <em>may</em> throw an
{@code IllegalStateException} when the {@code Publisher} completes.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code timeout} does not operate by default on any {@link Scheduler}.</dd>
</dl>

@param <U>
the first timeout value type (ignored)
@param <V>
the subsequent timeout value type (ignored)
@param firstTimeoutIndicator
a function that returns a Publisher that determines the timeout window for the first source
item
@param itemTimeoutIndicator
a function that returns a Publisher for each item emitted by the source Publisher and that
determines the timeout window in which the subsequent source item must arrive in order to
continue the sequence
@return a Flowable that mirrors the source Publisher, but notifies Subscribers of a
{@code TimeoutException} if either the first item or any subsequent item doesn't arrive within
the time windows specified by the timeout selectors
@see <a href="http://reactivex.io/documentation/operators/timeout.html">ReactiveX operators documentation: Timeout</a>