Why won't this shutdownhook work?

Question

This is my main method and it contains a shutdownhook:

public static void main(String args[]) {
    Runtime.getRuntime().addShutdownHook(new Thread() {
        @Override
        public void run() {
            JOptionPane.showMessageDialog(null, "Shutdown hook");
        }
        });

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(
            new Runnable() {
                @Override
                public void run() {
                    Thread.setDefaultUncaughtExceptionHandler(new MyUncaughtExceptionHandler());
                    MyFrame frame = new MyFrame();
                    frame.setVisible(true);
                }
            });
}

The problem is the JOptionPane doesn't show up at all. Instead, the frame closes but the app itself still runs. PS. I can't use the WindowClosing event because it doesn't fire on the Cmd+Q command on Mac OS X.

Maybe its because the awt event dispatcher was already shutdown when shutdown hooks are executed? — SpaceTrucker, Mar 21 '13 at 11:56
From the the javadoc of addShutdownHook: `Shutdown hooks should also finish their work quickly.` So I guess displaying a dialog is a really bad idea. You should rethink why you need a shutdown hook. — SpaceTrucker, Mar 21 '13 at 12:02
Whatever they are good for, interacting with the GUI is way beyond that. — Marko Topolnik, Mar 21 '13 at 12:03
OK - so apparently showing a pop up message from shutdown hooks is a bad idea. I guess I'll try something else. Thanks all. — Igor, Mar 21 '13 at 12:04

score 2 · Accepted Answer · answered Mar 21 '13 at 12:03

The dispatch thread is already shut down, or is likely to be shut down before your submission to the queue is executed.

You need to find another way of trapping the quit events, shutdown hook is there so you can tidy up when the VM is exiting, so you really don't want to by tying up more resources in the UI when it is called.

Why won't this shutdownhook work?

1 Answers1

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