Java Thread Ping Pong example

Question

I\'m trying to understand thread basics, and as a first example I create two thread that write a String on the stdout. As I know the scheduler allows to execute the threads

Answer 1

Here is a version that uses Semaphore objects to accomplish synchronization:

import java.util.concurrent.*;

public class Main {
    @FunctionalInterface
    public interface QuadFunction {
        public R apply(T t, U u, V v, W w);
    }

    public static void main(String[] args) {
        ExecutorService svc = Executors.newFixedThreadPool(2);

        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            System.out.println("Terminating...");
            svc.shutdownNow();
            try { svc.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS); }
            catch(InterruptedException e) {};
        }));

        var sem1 = new Semaphore(1);
        var sem2 = new Semaphore(0);

        QuadFunction fun =
            (name, action, s1, s2) ->
                (Runnable) () -> {
                    try {
                        while (true) {
                            s1.acquire();
                            System.out.format("%s %s\n", name, action);
                            Thread.sleep(500);
                            s2.release(1);
                        }
                    } catch (InterruptedException e) {}
                    s2.release(1);
                    System.out.format("==> %s shutdown\n", name);
                };

        svc.execute(fun.apply("T1", "ping", sem1, sem2));
        svc.execute(fun.apply("T2", "pong", sem2, sem1));
    }
}