src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler, boolean requestOn) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new FlowableSubscribeOn<T>(this, scheduler, requestOn));
    }
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler, boolean requestOn) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new FlowableSubscribeOn<T>(this, scheduler, requestOn));
    }
Asynchronously subscribes Subscribers to this Publisher on the specified {@link Scheduler}
optionally reroutes requests from other threads to the same {@link Scheduler} thread.
<p>
If there is a {@link #create(FlowableOnSubscribe, BackpressureStrategy)} type source up in the
chain, it is recommended to have {@code requestOn} false to avoid same-pool deadlock
because requests may pile up behind an eager/blocking emitter.
<p>
<img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/subscribeOn.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator doesn't interfere with backpressure which is determined by the source {@code Publisher}'s backpressure
behavior.</dd>
<dt><b>Scheduler:</b></dt>
<dd>You specify which {@link Scheduler} this operator will use.</dd>
</dl>
<p>History: 2.1.1 - experimental
@param scheduler
the {@link Scheduler} to perform subscription actions on
@param requestOn if true, requests are rerouted to the given Scheduler as well (strong pipelining)
if false, requests coming from any thread are simply forwarded to
the upstream on the same thread (weak pipelining)
@return the source Publisher modified so that its subscriptions happen on the
specified {@link Scheduler}
@see <a href="http://reactivex.io/documentation/operators/subscribeon.html">ReactiveX operators documentation: SubscribeOn</a>
@see <a href="http://www.grahamlea.com/2014/07/rxjava-threading-examples/">RxJava Threading Examples</a>
@see #observeOn
@since 2.2