Learning RxJava - Second Edition

Nuances of subscribeOn()

It is important to note that the subscribeOn() operator has no practical effect with certain sources (and keeps a worker thread unnecessarily on standby until that operation terminates). This might be because an Observable already uses a Scheduler. For example, Observable.interval() will use Schedulers.computation() and will ignore any subscribeOn() you specify, as shown here:

import io.reactivex.rxjava3.core.Observable;import io.reactivex.rxjava3.schedulers.Schedulers;public class Ch6_11 {    public static void main(String[] args) {        Observable.interval(1, TimeUnit.SECONDS)                .subscribeOn(Schedulers.newThread())                .subscribe(i -> System.out.println("Received " + i +                   " on thread " + Thread.currentThread().getName()));        sleep ...