tester.java

package fogus.rete;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.ref.WeakReference;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ThreadFactory;

public class Tester {
    static CompletableFuture<String> future = new CompletableFuture<>();

    private static WeakReference<Thread> startAndWrap(ThreadFactory factory, Runnable task) {
        Thread thread = factory.newThread(task);
        thread.start();

        System.out.println("THREAD KS == " + Thread.getAllStackTraces().keySet());
        System.out.println(" has? " + Thread.getAllStackTraces().containsKey(thread));

        return new WeakReference<>(thread);
    }

    @SuppressWarnings("removal")
    public static void main(String[] args) throws InterruptedException {
        String value = System.getProperty("jdk.trackAllThreads");
        System.out.println("jdk.trackAllThreads = " + value);

        RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
        String processName = runtimeMXBean.getName();
        long pid = Long.parseLong(processName.split("@")[0]);
        System.out.println("The Process ID (PID) of this Java application is: " + pid);

        ThreadFactory virtualThreadFactory = Thread.ofVirtual()
                .name("vthread-", 0)
                .uncaughtExceptionHandler((thread, throwable) -> {
                    System.err.println("Exception in " + thread.getName() + ": " + throwable.getMessage());
                })
                .factory();

        WeakReference ref = startAndWrap(virtualThreadFactory, () -> {
            try {
                System.out.println("Virtual thread blocking on future...");
                String result = future.get(); // This will block indefinitely
                System.out.println("Got result: " + result);
            } catch (InterruptedException | ExecutionException e) {
                System.out.println("Exception in vthread: " + e.getMessage());
            }
        });

        // Give the vthread time to start and block
        Thread.sleep(100);

        // Drop the future reference
        System.out.println("Dropping future reference...");
        future = null;

        // Force a GC
        System.out.println("Forcing GC...");
        System.gc();
        System.runFinalization();
        System.gc();

        // Keep main thread alive to observe the state
        Thread.sleep(6000);

        System.out.println("weakref value is " + ref.get());
        System.out.println("Exiting main thread.");
    }
}