How does one guarantee that an ScheduledExecutorService is running on the EDT?

java, swing, thread-safety

Solution

In your code:

ScheduledExecutorService ex = Executors.newSingleThreadScheduledExecutor();
SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            ex.schedule(new UpdatingService(), 1, TimeUnit.MILLISECONDS);
        }
    });

The only code executed on the EDT here is the `ex.schedule` invocation. The code that is then invoked by the scheduler later, eg `new UpdatingService()` will run on the thread that is internal to the scheduler, which will not be the EDT but some thread created by the call to `Executors.newSingleThreadScheduledExecutor`

Perhaps what I would do is have your scheduler schedule an update method (your updating service perhaps), which itself then puts a call onto the EDT via invokeLater.

Eg, something like:

ScheduledExecutorService ex = Executors.newSingleThreadScheduledExecutor();
ex.schedule(new Updater(), 1, TimeUnit.MILLISECONDS);
...
class Updater extends Runnable {
    @Override
    public void run() {
      // invoke the EDT via Swing Utilities here.     
    }
}

This is my best advice without seeing what the rest of your code is doing.

Problem

While working on the animation and updating timer for a game, I read that any activities relating to the GUI should be run on the EDT, including repainting the screen. I am using a single `ScheduledExecutorService` to update and draw the game (using active rendering). The initial schedule to the service (which is a nested class that `implements Runnable`) is done in a call like this: ``` ScheduledExecutorService ex = Executors.newSingleThreadScheduledExecutor(); SwingUtilities.invokeLater(new Runnable() { @Override public void run() { ex.schedule(new UpdatingService(), 1, TimeUnit.MILLISECONDS); } }); ``` I thought that this would make the service run on the EDT but adding `System.out.println(SwingUtilities.isEventDispatchThread());` proved that it was not. I did some searching and found this post that mentioned starting the EDT inside the timer. I tried this and it does work. However, it doesn't seem like a good idea to nest Threads like that. So, is nesting Threads like this not as bad as it seems? And if it is a bad idea, then what would be the proper way to ensure that a `ScheduledExecutorService` is running on the EDT?

Original source