RxJava2可观察到的背压

Question

recently I realized that I don't understand how RxJava2 backpressure works.

I made small test and I expect that it should fail with MissingBackpressureException exception:

@Test
public void testBackpressureWillFail() {
    Observable.<Integer>create(e -> {
        for (int i = 0; i < 10000; i++) {
            System.out.println("Emit: " + i);
            e.onNext(i);
        }
        e.onComplete();
    })
    .subscribeOn(Schedulers.newThread())
    .observeOn(Schedulers.computation())
    .doOnNext(i -> {
        Thread.sleep(100);
        System.out.println("Processed:" + i);
    })
    .blockingSubscribe();
}

System out shows next:

Emit: 0
Emit: 1
Emit: 2
...
Emit: 10000

Processed:0
Processed:1
Processed:2
...
Processed:10000

Why it doesn't produce MissingBackpressureException .

I expect that e.onNext(i); will put item into buffer of ObservableObserveOn and after it's size is greater than static final int BUFFER_SIZE = Math.max(16,Integer.getInteger("rx2.buffer-size",128).intValue());

It should throw MissingBackpressureException which doesn't happen. Does the buffer automatically grow? If not where are items stored?

Answer 1

That's because backpressure moved out to Flowable only with RxJava2, see here .
If you will switch to Flowable with BackpressureStrategy.MISSING you will get the exception.
That also means that in your case you indeed have buffer that automatically grows, from observerOn docs:

Modifies an ObservableSource to perform its emissions and notifications on a specified Scheduler, asynchronously with an unbounded buffer ...