Unhandled reactor.core.Exception OverflowException: Queue is full?!

[brisote]

While I'm playing around with the new reactive features in Spring Boot v2.0.0.BUILD-SNAPSHOT I have noticed that when I multiple time force close the connection to endpoint like this:

    @GetMapping(produces = MediaType.TEXT_EVENT_STREAM_VALUE, value = "/events")
    public Flux<Event> getEvents()
    {
        return Flux.from(new Publisher<Event>() {
            @Override
            public void subscribe(Subscriber<? super Event> subscriber) {
                while (true) {
                    try {
                        new Thread().sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                    subscriber.onNext(new Event(1, new Date()));
                }
            }
        });
    }

Spring throws: "reactor.core.Exceptions$BubblingException: reactor.core.Exceptions$OverflowException: Queue is full?!" and after that when I call the endpoint again it freeze. Here I've created a repo https://github.com/georgi-staykov/reactive-demo where you can find example code and video that shows the bug.

[philwebb]

It's likely that we'll need help with this one from either the WebFlux team or the Reactor team. /cc @bclozel @rstoyanchev @smaldini.

[snicoll]

That's definitely a non Spring Boot issue anyway and that blocking code is "unusual". Please join the #reactor room on gitter if you have question about using flux and mono. You can also create a new thread on stackoverflow.

[brisote]

I don't know where the bug is ( spring or reactor) and what is "unusual" but the fact is that the endpoint (that spring exposes) is freezing which is not acceptable in any circumstances in my opinion.

[snicoll]

I don't know either but it's not in spring boot and freezing a thread in such environment is just wrong.

[rstoyanchev]

There are many problems with this sample. To start it's not a Reactive Streams compliant Publisher since it calls onNext before calling onSubscribe and then completely ignores back-pressure by pushing items without a corresponding request for items from the Subscriber (i.e. the server). It also blocks the current thread which will quickly kill it (with a few concurrent users) that's running event-loop style with just a few threads based on the number of cores.

The whole point of using Reactor Flux is that you don't have to implement Publisher from scratch. Use Flux#create or for this scenario use Flux#interval.