How to get all elements immediately in other threads in Subscriber in RxJava?

Question

If i execute such a code:

    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    Flowable.fromIterable(Lists.newArrayList(1, 2, 3, 4, 5, 6))
            .subscribeOn(Schedulers.io())
            .subscribe(new Consumer<Integer>() {
                @Override
                public void accept(Integer integer) throws Throwable {
                    System.out.println(stopWatch + " value:" + integer);
                    Thread.sleep(1000);
                }
            });
    Thread.sleep(100000);

In output, i get each element just after sleep time, like this:

00:00:00.027 value:1
00:00:01.030 value:2
00:00:02.030 value:3
00:00:03.031 value:4
00:00:04.031 value:5
00:00:05.031 value:6

but as i understand, if i use Schedulers.io(), than i must get all the values parallel, and i expected, that i will get all values immediately, than i will wait 1000 mills just once, and thats all

Like this:

00:00:00.027 value:1
00:00:00.030 value:2
00:00:00.030 value:3
00:00:00.031 value:4
00:00:00.031 value:5
00:00:00.031 value:6

How can i get them all in other threads, NOT one by one?

I dont wanna them to wait each other

I try Schedulers.computation() and other, but they still arrive one by one

How to get them all immediately?

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Answer 1

if i use Schedulers.io(), than i must get all the values parallel

No. RxJava flows are sequential by default, which means items are delivered one after the other. If your consumer blocks or sleeps, subsequent items are delayed every time.

How can i get them all in other threads, NOT one by one?

Use parallel :

StopWatch stopWatch = new StopWatch();
stopWatch.start();
Flowable.fromIterable(Lists.newArrayList(1, 2, 3, 4, 5, 6))
        .parallel()
        .runOn(Schedulers.io())
        .doOnNext(new Consumer<Integer>() {
            @Override
            public void accept(Integer integer) throws Throwable {
                System.out.println(stopWatch + " value:" + integer);
                Thread.sleep(1000);
            }
        })
        .sequential()
        .subscribe();

Thread.sleep(100000);

Recommended reading: https://github.com/ReactiveX/RxJava#parallel-processing