Reactor Scheduler with anonymous thread

Question

I'm testing how reactor works, created such code which is quite similar to what can be found in reactor documentation.

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Scheduler;
import reactor.core.scheduler.Schedulers;

@SpringBootTest
@RunWith(SpringRunner.class)
public class ReactorApplicationTests {

  @Test
  public void publishOnThreadTest() {
    Scheduler s = Schedulers.newParallel("parallel-scheduler", 4);

    final Mono<String> mono = Mono.just("Publish on test: \n")
            .map(msg -> msg + "before: " + Thread.currentThread() )
            .publishOn(s)
            .map(msg -> msg + "\nafter: " + Thread.currentThread());

    new Thread(() -> mono.subscribe(System.out::println)).start();
  }
}

And I cannot make it run, what am I doing wrong? With just subscribe it works but I wanted to look at thread used and play a bit with it.

Answer 1

The reason your test program prints nothing is because it exits too early. It should wait until substriber's method is called:

@Test
public void publishOnThreadTest() throws InterruptedException {
    Scheduler s = Schedulers.newParallel("parallel-scheduler", 4);
    CountDownLatch latch = new CountDownLatch(1);

    final Mono<String> mono = Mono.just("Publish on test: \n")
            .map(msg -> msg + "before: " + Thread.currentThread() )
            .publishOn(s)
            .map(msg -> msg + "\nafter: " + Thread.currentThread());

    new Thread(() -> mono.subscribe((String str) ->{
        System.out.println(str);
        latch.countDown();
    })).start();

    latch.await();
}