CountDownLatch Coordination

CountDownLatch Coordination

Save as Main.java and run with a Java 17+ JDK: java Main.java.

import java.util.concurrent.CountDownLatch;

public class Main {
  public static void main(String[] args) throws Exception {
    CountDownLatch done = new CountDownLatch(1);
    int[] result = new int[1];
    Thread worker = new Thread(() -> {
      try { result[0] = 42; }
      finally { done.countDown(); }
    });
    worker.start();
    done.await();
    System.out.println(result[0]);
    worker.join();
  }
}

1. Expected output: 42
2. Actions before countDown become visible after the matching successful await. The finally block releases the waiter if the worker body fails.