Rx - utility_subscribeon

SubscribeOn

SubscribeOn specify the Scheduler on which an Observable will operate.

Many implementations of ReactiveX use “Schedulers” to govern an Observable’s transitions between threads in a multi-threaded environment. You can instruct an Observable to do its work on a particular Scheduler by calling the Observable’s SubscribeOn operator.

By default, an Observable and the chain of operators that you apply to it will do its work, and will notify its observers, on the same thread on which its Subscribe method is called. The SubscribeOn operator changes this behavior by specifying a different Scheduler on which the Observable should operate. The ObserveOn operator specifies a different Scheduler that the Observable will use to send notifications to its observers.

As shown in this illustration, the SubscribeOn operator designates which thread the Observable will begin operating on, no matter at what point in the chain of operators that operator is called. ObserveOn, on the other hand, affects the thread that the Observable will use below where that operator appears. For this reason, you may call ObserveOn multiple times at various points during the chain of Observable operators in order to change on which threads certain of those operators operate.

Example:

fun subscribeOn() {
        Observable.create<Int> {
            it.onNext(1)
            it.onComplete()
        }
        .subscribeOn(Schedulers.newThread())
        .subscribe { println("Subscriber on ${Thread.currentThread().name}") }
}

Output:

Subscriber on RxNewThreadScheduler-1

Links

SubscribeOn

Further reading

RxJava2 subscribeOn: How to use it

credit goes to @swayangjit