The Window boundary is not respect.

Hi All,

I creating a library for communicate with REST endpoint. I have to buffer REST request and sent its together in the batch, but also I want to have a possibility to flush buffer.

Here is the snippet of my implementation:

PublishProcessor<Flowable<String>> flush = PublishProcessor.create();
PublishProcessor<String> restProcessor = PublishProcessor.create();

int count = 2;
int delay = 100;

TestScheduler scheduler = new TestScheduler();

Flowable<Flowable<String>> boundary = restProcessor.window(delay, TimeUnit.MILLISECONDS, scheduler, count, true)
                .mergeWith(flush);

restProcessor
                .window(boundary)
                .concatMapSingle(Flowable::toList)
                .filter(it -> !it.isEmpty())
                .subscribe(strings -> System.out.println("emit REST call >>> " + strings));

The problem is that the restProcessor first emit a value with single element instead of two.

restProcessor.offer("1");
restProcessor.offer("2");

restProcessor.offer("3");
restProcessor.offer("4");

restProcessor.offer("5");
restProcessor.offer("6");

restProcessor.offer("7");
restProcessor.offer("8");

restProcessor.offer("9");
flush.offer(Flowable.just("flush"));

restProcessor.offer("10");

System.out.println("onComplete");

restProcessor.onComplete();
flush.onComplete();

Result

emit REST call >>> [1]
emit REST call >>> [2, 3]
emit REST call >>> [4, 5]
emit REST call >>> [6, 7]
emit REST call >>> [8, 9]
onComplete
emit REST call >>> [10]

I think that the result should be:

emit REST call >>> [1, 2]
emit REST call >>> [3, 4]
emit REST call >>> [5, 6]
emit REST call >>> [7, 8]
emit REST call >>> [9]
onComplete
emit REST call >>> [10]

The Junit test for reproduce is here (Gist)

RxJava version

io.reactivex.rxjava2:rxjava:2.2.4.

Java version

java version “1.8.0_152”

[akarnokd]

Works as intended. What happens is that the boundary fires before the main sequence gets 2, thus 2 ends up in the subsequent window. You have to swap the order of the consumers to the restProcessor via another processor:

PublishProcessor<Flowable<String>> flush = PublishProcessor.create();
PublishProcessor<String> restProcessor = PublishProcessor.create();

int count = 2;
int delay = 100;

TestScheduler scheduler = new TestScheduler();

Flowable<Flowable<String>> boundary = restProcessor.window(
        delay, TimeUnit.MILLISECONDS, scheduler, count, true)
                .mergeWith(flush);

// defer the subscription to the real boundary
PublishProcessor<Flowable<String>> tempBoundary = PublishProcessor.create();

restProcessor
                .window(tempBoundary)
                .concatMapSingle(Flowable::toList)
                .filter(it -> !it.isEmpty())
                .subscribe(strings -> System.out.println("emit REST call >>> " + strings));

// now subscribe to the actual boundary, this will make sure `restProcessor` has boundary as
// a second consumer.
boundary.subscribe(tempBoundary);

restProcessor.offer("1");
restProcessor.offer("2");

restProcessor.offer("3");
restProcessor.offer("4");

restProcessor.offer("5");
restProcessor.offer("6");

restProcessor.offer("7");
restProcessor.offer("8");

restProcessor.offer("9");
flush.offer(Flowable.just("flush"));

restProcessor.offer("10");

System.out.println("onComplete");

restProcessor.onComplete();
flush.onComplete();

[akarnokd]

Why did you add that observeOn in the first place? If you need asynchrony, move it further away from the windowing logic.