Do something after method returns

Question

This is my situation in pseudocode:

function onRequest() {
    receiveConnectionRequest();

    response = function onConnect() {
        playersConnected++;
        if (playersConnected == 4) {
            sendAllPlayersTheirCards()
        }
        return OK;
    }();

    sendResponse(response);

}

When players 1-3 connect, they get added to the list of players and OK is returned to them, at which point they will set stuff up on their side. When player 4 connects, however, before the response to his request is sent, all players are sent their cards. Because player 4 has not received a response to his request yet, he hasn't initialised correctly yet and errors upon receiving his cards.

What I'd like to have is this:

function onRequest() {
    receiveConnectionRequest();

    response = function onConnect() {
        playersConnected++;
        if (playersConnected == 4) {
            plan(sendAllPlayersTheirCards())
        }
        return OK;
    }();

    sendResponse(response);

    executePlanned() // now cards are sent
}

Is there a general pattern for that? The onConnect function is in a different class and should not be aware of the implementation details of onRequest.

I'm specifically trying to implement this in Java, but generic solutions are welcome.

Answer 1

Many good solutions to this, but I would suggest using a call back.

Don't think of it as doing something after the method returns, think of it as calling back to report a state or trigger an event.

Search for event pattern , or call backs in Java. Here is one link I found.

The delegation pattern is very similar to.

Answer 2

Can you not send the response first and then do the "if(playersConnected" check after?

Answer 3

I'm not sure about this closure syntax you have here. Can you just have this instead?

function onRequest() {
    playersConnected++;

    sendResponse(OK);

    if (playersConnected == 4) {
        sendAllPlayersTheirCards()
    }
}

Answer 4

I could do it like this:

function onRequest(request) {

 game.handleRequest(request, function(response) {
  sendResponse(response);
 }

}

class game
function handleRequest(request, sendResponse:Function) {
 players++;
 sendResponse(OK);
 if (players == 4) sendCards();
}

Answer 5

This seems like a relevant tutorial:

Using Callable to Return Results From Runnables