I have following code with a try-with-resources which creates two resources and it works fine:

public class SimpleResourceExample {

    public static void main(String... args) {
        try (var resource1 = new Resource(1);
             var resource2 = new Resource(2)) {
            System.out.println("Using "+resource1 +" and "+resource2);
            Thread.sleep(20 * 1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    private record Resource(int id) implements AutoCloseable {
        @Override
        public void close() {
            System.out.println("Closing resource "+id);
        }
    }
}

So when I run it I get following output (in 20 seconds):

Using Resource[id=1] and Resource[id=2]
Closing resource 2
Closing resource 1

Process finished with exit code 0

And when I add below code (in main(), just before try-with-resources), to interrupt the thread, it also works fine:

        var t = Thread.currentThread();
        new Thread(() -> {
            try {
                Thread.sleep(10 * 1000);
                t.interrupt();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }).start();

So this new thread interrupts the main thread after 10 seconds and the resources are also closed, with below output:

Using Resource[id=1] and Resource[id=2]
Closing resource 2
Closing resource 1
Exception in thread "main" java.lang.RuntimeException: java.lang.InterruptedException: sleep interrupted
    at ....

Process finished with exit code 1

(stack trace omitted for brevity)

But when I introduce a shutdown-hook with below code:

        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            System.out.println("Shutting down");
            t.interrupt();
        }));

And trigger it with this command:

kill -15 <PID> 

I get following output:

Using Resource[id=1] and Resource[id=2]
Shutting down

Process finished with exit code 143 (interrupted by signal 15:SIGTERM)

This means it gets the signal and stops the application. And I think it also sends the interrupt to the main thread, but it doesn’t close resources.

Does anybody why this happens and how to ensure the resources are closed?
Thanks.