Question

I want to save an object (my game’s model/data) to disk, but as the game can get quite large – feasibly large enough to take several game ticks to store – I’m thinking it makes sense to perform the saving in a separate thread in order to keep the game running relatively smoothly.

What is the best method to achieve this? I wasn’t sure if it made sense to make the GameState (the model) a runnable or an extension of Thread, because most of the time it isn’t intended to be Runnable – logically, then, it shouldn’t be Runnable?

Other possibilities I’ve looked at are to have a Runnable GameSaver class, to which I pass the GameState or a copy of the GameState. Presumably, however, this would cause problems with synchronisation if I pass the GameState or will slow the game down while the class is cloned.

What’s the best approach, or the pro’s and con’s of approaches? Any other alternatives appreciated, too – I doubt my search has been exhaustive.

Answer 1

From a pure thread management perspective, the cleanest way I think is to use an executor. That does not solve your cloning (or not) issue.

Create a method that saves the game:

public void saveTheGame() {
    //you maybe need to take a snapshot, which might require synchronization
    GameState state = ....;
}

Create a runnable, as a class instance member for example, that embeds that call and an executor service:

private final Runnable save = new Runnable() {
    public void run() {
        saveTheGame();
    }
}
private final ExecutorService executor = Executors.newFixedThreadPool(1);

And save the game as and when needed:

executor.submit(save);

Don’t forget to shutdown the executor when closing your app:

executor.shutdown();

You can also use a ScheduledExecutorService instead that runs every x minutes for example.

The class might look like this for example:

public static class GameSaver {
    private final Runnable save = new Runnable() {

        @Override
        public void run() {
            saveGame();
        }
    };
    private static final ExecutorService executor = Executors.newFixedThreadPool(1);
    private final GameState state;

    public GameSaver(GameState state) {
        this.state = state;
    }

    public void save() {
        executor.submit(save);
    }

    public static void close() {
        executor.shutdown();
    }

    private void saveGame() {
        //save your game here
    }

}

and in your main code:

GameState state = getGameState();
GameSaver saver = new GameSaver(state);
saver.save();