vertx event bus blocking behaviour bug?

[bublag]

Hi,
I am not sure what I observed is a bug or intended behaviour, so I am posting a question here.

In the guide about using the vertx "EventBus", it is stated that the consuming of the events can be configured to be blocking:
https://quarkus.io/guides/reactive-event-bus#consuming-events

I made a small test project where I tested this and it seems that the publisher is not blocked until the consumer is finished.

Test project:
https://github.com/bublag/test-quarkus-event-bus-blocking
Used Quarkus version: 3.28.3

This is how my publisher method looks:
https://github.com/bublag/test-quarkus-event-bus-blocking/blob/a6c625ccc841412f1d366903c379fddbe90c49b5/src/main/java/org/acme/vertx/VertxEventPublisher.java#L16

@ApplicationScoped
public class VertxEventPublisher {

	@Inject
	EventBus eventBus;

	@Scheduled(every = "1s", identity = "scheduledVertxEvent")
	public void scheduledVertxEvent() {
		Log.info(System.lineSeparator());
		eventBus.publish("vertxEvent1", "greeting1");
		eventBus.publish("vertxEvent2", "greeting2");
	}
}

It sends messages into two different addresses: message greeting1 into address vertxEvent1, and greeting2 into address vertxEvent2.

Here is my consumer:
https://github.com/bublag/test-quarkus-event-bus-blocking/blob/a6c625ccc841412f1d366903c379fddbe90c49b5/src/main/java/org/acme/vertx/VertxEventConsumer.java

@ApplicationScoped
public class VertxEventConsumer {

	@ConsumeEvent(value = "vertxEvent1", blocking = true)
	void consume1(String message) throws InterruptedException {
		Log.info(message + "start");
		Thread.sleep(100);
		Log.info(message + "end");
	}

	@ConsumeEvent(value = "vertxEvent2", blocking = true)
	void consume2(String message) throws InterruptedException {
		Log.info(message + "start");
		Thread.sleep(100);
		Log.info(message + "end");
	}
}

It listens to both addresses, notice the blocking = true parameter in the annotations. They wait a little to see if the code execution is really blocked.

When I run the application this is what I would expect from the logs:

greeting1start
greeting1end
greeting2start
greeting2end

But this is what happens:

...
2025-10-16 16:38:30,025 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-3) greeting1start
2025-10-16 16:38:30,025 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-2) greeting2start
2025-10-16 16:38:30,131 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-3) greeting1end
2025-10-16 16:38:30,131 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-2) greeting2end
2025-10-16 16:38:31,014 INFO [org.acm.ver.VertxEventPublisher] (vert.x-worker-thread-2)
2025-10-16 16:38:31,014 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-2) greeting2start
2025-10-16 16:38:31,014 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-3) greeting1start
2025-10-16 16:38:31,122 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-3) greeting1end
2025-10-16 16:38:31,122 INFO [org.acm.ver.VertxEventConsumer] (vert.x-worker-thread-2) greeting2end
2025-10-16 16:38:32,015 INFO [org.acm.ver.VertxEventPublisher] (vert.x-worker-thread-2)
...

Is this a bug, or my expectation is wrong?

P.S. I also checked how the same behaves with the "jakarta event bus", and that one works how I expected the blocking behaviour should work. It is commented out here in my test project:
https://github.com/bublag/test-quarkus-event-bus-blocking/blob/a6c625ccc841412f1d366903c379fddbe90c49b5/src/main/java/org/acme/jakarta/JakartaEventPublisher.java#L19
and the consumer for that:
https://github.com/bublag/test-quarkus-event-bus-blocking/blob/a6c625ccc841412f1d366903c379fddbe90c49b5/src/main/java/org/acme/jakarta/JakartaEventConsumer.java