Is there a better way than using java Completable to do that kind of things :

val result= CompletableFuture<String>()
        eventBus.consumer<context.Context>(eventName, this).completionHandler { 
            if(it.succeeded()){
                <http://logger.info|logger.info>("Register ${this::class.simpleName} for event $eventName")
                result.complete(this::class.simpleName)
            }else{
                logger.error("Unable to register ${this::class.simpleName} for event $eventName")
                result.completeExceptionally(UnableToRegisterServiceTaskException())
            }            
        }
        return result

Take a look at Kotlin coroutines. It typically enables you to write clean, sequential code for your concurrent tasks