Blocking @ConsumeEvent only uses single worker thread since 1.11.X

[kkosmrli]

Description

Greetings,

while upgrading our Quarkus services from 1.10.4 to 1.11.3 we noticed that the behaviour of the Vert.x event bus significally changed. The event bus does not utilize more than one thread from the worker thread pool and the execution of multiple events is therefore not concurrent as it was prior to 1.11.X.

I could not find any hints in the changelogs or the migration guide why the behaviour changed.

If this new behaviour is indeed expectec, how can we handle the conccurrent execution of events if we do not want to use reactive style code?

Expected behavior

ConsumeEvent with blocking=true should utilize all available worker pool threads and execute events concrrently.

Actual behavior

The execution of events seems to only use a single worker thread and does not execute events concurrently.

Example Code

Bean with some long running job:

@Dependent
public class SomeJobClass {

    private static final Logger LOG = Logger.getLogger(SomeJobClass.class);

    public void longRunningJob(String test) {
        LOG.info("Executing");
        try {
            Thread.sleep(1000l);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        LOG.info("finished");
    }
}

The class containing the consumer:

@ApplicationScoped
public class ConsumerClass {

    @Inject
    SomeJobClass importer;

    @ConsumeEvent(value = "test", blocking = true)
    void test(String event) {
        importer.longRunningJob(event);
    }
}

Send 2 events:

@Test
@DisplayName("Some Test")
void testConcurrentEvents() throws InterruptedException {
    eventBus.send("test", "1");
    eventBus.send("test", "1");

    Thread.sleep(3000l);
    }

Log output with Quarkus 1.11.2.FINAL:

2021-02-26 13:53:29,994 INFO  [foo] (vert.x-worker-thread-0) Executing
2021-02-26 13:53:30,997 INFO  [foo] (vert.x-worker-thread-0) finished
2021-02-26 13:53:30,998 INFO  [foo] (vert.x-worker-thread-0) Executing
2021-02-26 13:53:32,002 INFO  [foo] (vert.x-worker-thread-0) finished

Log output with Quarkus 1.10.5.FINAL:

2021-02-26 14:02:19,345 INFO  [foo] (vert.x-worker-thread-0) Executing
2021-02-26 14:02:19,345 INFO  [foo] (vert.x-worker-thread-1) Executing
2021-02-26 14:02:20,349 INFO  [foo] (vert.x-worker-thread-0) finished
2021-02-26 14:02:20,349 INFO  [foo] (vert.x-worker-thread-1) finished

The logs show that the execution with version 1.11.2.FINAL was not concurrent and is using only vert.x-worker-thread-0.

[cescoffier]

#15366 should fix it.