Uni().onFailure().withBackoff(x,y).atMost(z) is executed on a worker thread causing Hibernate-Reactive to throw

[dimitar-epitropov]

We've hit an issue where using Uni retry with backOff and at Most hits this code:

    @CheckReturnValue
    public Uni<T> atMost(long numberOfAttempts) {
        if (!backOffConfigured) {
            return Infrastructure.onUniCreation(new UniRetryAtMost<>(upstream, onFailurePredicate, numberOfAttempts));
        } else {
            Function<Multi<Throwable>, Publisher<Long>> factory = ExponentialBackoff
                    .randomExponentialBackoffFunction(numberOfAttempts,
                            initialBackOffDuration, maxBackoffDuration, jitter, Infrastructure.getDefaultWorkerPool());
            return upstream.toMulti().onFailure(onFailurePredicate).retry().when(factory).toUni();
        }
    }

We can see that if backOffConfigured is true then the code is executing on a worker pool. This causes hibernate-reactive to throw as it expects to be on the eventloop. Is it possible to keep using backOff configuration but to execute on event-loop thread?

Is the fact that retries with backOff are executed on the worker-pool due to technological limitations (waiting during backoff is blocking). Will there ever be a possibility to do it on the event-loop thread?

[jponge]

We need a scheduled executor to perform the backoff logic, else we would indeed block an event-loop.

Vert.x offers ways to execute an action back to the original event-loop context, see https://vertx.io/docs/apidocs/io/vertx/core/Context.html#runOnContext-io.vertx.core.Handler-