java shutdown hook with more than one thread

Question

I am trying to get a shutdown hook to work on my ubuntu server, however I seem to have an issue with more than one thread. Using the a basic ShutdownHook, the following bit of code does work when I kill the process using kill <PID>, meaning the shutdown behavior is activated.

public static void main(String[] args) {
    ShutdownHook shutDown = new ShutdownHook();
    shutDown.attachShutDownHook();

    while(true){}
}

however this same code with an additional thread does not

public static void main(String[] args) {
    ShutdownHook shutDown = new ShutdownHook();
    shutDown.attachShutDownHook();

    (new Thread() {
        public void run() {
            while ( true ) {}
        }
    }).start();

    while(true){}
}

Any ideas?

class ShutdownHook {

    ShutdownHook() {
    }

    public void attachShutDownHook() {

            Runtime.getRuntime().addShutdownHook(new Thread() {
                    @Override
                    public void run() {
                            System.out.println("Shut down hook activating");
                    }
            });
            System.out.println("Shut Down Hook Attached.");

    }
}

Answer 1

The JVM won't exit while there are still non-daemon threads running. Try calling setDaemon(true) on your new thread.