Process does not terminate after calling System.exit in daemon thread

[quijote]

There seems to be a regression introduced with 0.21 that results in process not terminating after user code calls System.exit in a daemon thread.

Probably related to:
#9516
#9558

I can reproduce this with the following code:

public class Launchee {
	public static void main(String[] args) throws Exception {
		final CountDownLatch latch = new CountDownLatch(1);
		Thread t = new Thread() {
			@Override
			public void run() {
				latch.countDown();
				System.exit(1);
			}
		};
		t.setDaemon(true);
		t.start();
		latch.await();
	}
}

This sometimes hangs when executed with AdoptOpenJDK OpenJ9 8.0.262.10. Similar problem was observed with 11.0.8.10.0 and 14.0.2.12.0.

I simply launched this in a loop:

public class Launcher {
    public static void main(String[] args) throws Exception {
        int i = 0;
        while (true) {
            System.out.println(i++);
            List<String> commandLine = new ArrayList<>();
            commandLine.add("adoptopenjdk-openj9_64-8.0.262.10.0\\bin\\java.exe");
            commandLine.add("-cp");
            commandLine.add("bin");
            commandLine.add("Launchee");
            ProcessBuilder pb = new ProcessBuilder(commandLine);
            pb.inheritIO();
            Process process = pb.start();
            process.waitFor();
        }
    }        
}

With Hotspot and previous JVMs I get

0
1
2
...

With OpenJ9 0.21 I sometimes just get:

0

and then it hangs forever.

[pshipton]

@gacholio fyi

If I run Launchee on Linux with a recent build, it hangs, needs to be killed with -9.

[gacholio]

I can see what's wrong, but I'll need some time to think about how to fix it.

[gacholio]

Here's the hang scenario:

main                                        daemon

DestroyJavaVM                               call System.exit()
indicate exit stared
                                            java enters monitor
                                            exitJavaVM()
                                            detect exit started, block forever (as intended)
call Shutdown.shutDown()
java blocks entering monitor

[gacholio]

The solution appears to be moving the "indicate exit started" to after the call to Shutdown.shutdown(). This still protects against multiple VMDeath events and exit during VMDeath.

[quijote]

Thank you for the quick fix. I did not quite follow the comment that CountDownLatch does not exist in Java 8 (it was introduced with Java 5).

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CountDownLatch.html

[gacholio]

OK, my mistake - I had never seen it used until very recently, so I assumed it was new.