spring-bootreactive-programmingproject-reactorspring-reactivespring-reactor

Schdulers.elastic not creating new threads in Reactor

I am trying to create a flow where a flux emits 10 items, each in parallel, with each item sleeping for 1s. Since each item is being published on a separate thread, I expect the entire process to take 1s. But the logs show that it's taking 10s instead.

I tried changing subscribeOn to publishOn, map to doOnNext. But none of them seem to work.

I am new to Reactor and am trying to understand where I am going wrong. Any help would be most appreciated. Thanks

    public void whenIsANewThreadCreated() {
        Flux.range(1,10)
                .publishOn(Schedulers.elastic())
                .map(count -> {
                    logger.info(Thread.currentThread().getName() + " - Sleeping for 1s" + " with count: " + count);
                    try {
                        Thread.sleep(1_000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    return count;
                })
        .blockLast();
    }

2020-03-30 16:17:29.799  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 1
2020-03-30 16:17:30.802  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 2
2020-03-30 16:17:31.804  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 3
2020-03-30 16:17:32.805  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 4
2020-03-30 16:17:33.806  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 5
2020-03-30 16:17:34.808  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 6
2020-03-30 16:17:35.809  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 7
2020-03-30 16:17:36.811  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 8
2020-03-30 16:17:37.812  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 9
2020-03-30 16:17:38.814  INFO 15744 --- [      elastic-2] com.example.demo.DemoApplicationTests    : elastic-2 - Sleeping for 1s with count: 10
Solution

  • You have to first create a parallel flux by calling parallel method and you have to use runOn to achieve parallelism.

    Flux.range(1,10)
    .parallel()
    .runOn(Schedulers.elastic())
    .map(count -> {
        System.out.println(Thread.currentThread().getName() + " - Sleeping for 1s" + " with count: " + count);
        try {
            Thread.sleep(1_000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return count;
    }).subscribe();