Vert.x: Verticle custom startFuture handler is always rewritten

Question

Vert.x v3.5.1. There is my custom start method of Verticle:

@Override
public void start(Future<Void> startFuture) throws Exception {
    startFuture.setHandler(event -> {
        if (event.succeeded()) {
            logger.info("Server started on port: {}", 8080);
        } else {
            logger.warn("Failed to start: {}", event.cause());
        }
    });
    vertx.createHttpServer()
            .requestHandler(router()::accept)
            .listen(8080, event -> {
                if (event.succeeded()) {
                    startFuture.complete();
                } else {
                    startFuture.fail(event.cause());
                }
            });
}

I expect that my custom handler will be invoked when future completes. But it doesn't! In debug mode I see that FutureImpl::setHandler is called twice: once with my custom handler, and then with DeploymentManager's handler during doDeploy. So the latest handler is applied.

The question is: is it possible to specify custom callback for Verticle start? If yes how can I do it?

Thank you in advance.

Answer 1

You're not supposed to change the handler of the startFuture, as it is owned by the caller. So simply, don't do that :) The future is used to signal that you're done with your start-code, and not to define what should be done, once you're done.

In your concrete example it'd be better to write the logs once the http server came up, and then indicate to the startFuture, that you're done with your code execution.

@Override
public void start(Future<Void> startFuture) throws Exception {
    vertx.createHttpServer()
         .requestHandler(router()::accept)
         .listen(8080, event -> {
            if (event.succeeded()) {
                logger.info("Server started on port: {}", 8080);
                startFuture.complete();
            } else {
                logger.warn("Failed to start: {}", event.cause());
                startFuture.fail(event.cause());
            }
         });
}