quarkus @ObservesAsync invoke Uni

Question

What's the best way to invoke Uni in an async observer? It would be great if I could just return Uni but unfortunately that doesn't work.

void observe(@ObservesAsync MyEvent event) {
    Uni<Object> task;
}

Answer 1

As mentioned by @ladicek, you can:

1. use a synchronous observer and block until termination
2. use a synchronous observer and "trigger" the async operation using a fire-and-forget approach
3. use an async observer (while it's not strictly async, it just runs on another thread) and produce a CompletionStage

1) Synchronous observer and block until termination

void observe(@Observes MyEvent event) {
    Uni<Void> uni = ...;
    uni.await().indefinitely();
}

2) Synchronous observer and trigger the async operation using a fire-and-forget approach

void observe(@Observes MyEvent event) {
    Uni<Void> uni = ...;
    uni.subscribeAsCompletionStage(); // Fire and forget, no error reporting
}

Or:

void observe(@Observes MyEvent event) {
    Uni<Void> uni = ...;
    uni.subscribe().with(success -> ..., failure -> log(failure));
}

3) Async observer and produce a CompletionStage

CompletionStage<Void> observe(@ObservesAsync MyEvent event) {
    Uni<Void> uni = ...;
    return uni.subscribeAsCompletionStage();
}