Java Phaser

//Listing 6-5. Using a Phaser to Control a One-Shot Action Serving a Variable Number
//of Parties
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.Phaser;

public class A {
    public static void main(String[] args)
{
    List<Runnable> tasks = new ArrayList<>();
    
    tasks.add(() -> System.out.printf("%s running at %d%n",
    Thread.currentThread().getName(),
    System.currentTimeMillis()));
    
    tasks.add(() -> System.out.printf("%s running at %d%n",
    Thread.currentThread().getName(),
    System.currentTimeMillis()));
    runTasks(tasks);
}

    static void runTasks(List<Runnable> tasks)
    {
        final Phaser phaser = new Phaser(1); // "1" (register self)
        // create and start threads
        for (final Runnable task: tasks)
        {
        phaser.register();
        Runnable r = () ->
        {
            try
            {
                Thread.sleep(50 + (int) (Math.random() * 300));
            }
            catch (InterruptedException ie)
            {
                System.out.println("interrupted thread");
            }
            phaser.arriveAndAwaitAdvance(); // await the ...
            // creation of ...
            // all tasks
            task.run();
        };
        
        Executors.newSingleThreadExecutor().execute(r);
        }
        // allow threads to start and deregister self
        phaser.arriveAndDeregister();
}
}