Main.java

import java.util.Objects;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class Main {

    public static void main(String[] args){
//        var cont = new Continuation(5, "unlucky");
//        for (int i = 0; i < 10; i++) {
//            cont = luck(cont);
//            System.out.println("my luck :" + cont.ret);
//        }
        var dispatcher = Executors.newFixedThreadPool(5);
        dispatcher.submit(new Callback("A",new Continuation(3, "unlucky"), dispatcher));
        dispatcher.submit(new Callback("B",new Continuation(1, "unlucky"), dispatcher));
        dispatcher.submit(new Callback("C",new Continuation(5, "unlucky"), dispatcher));
        dispatcher.submit(new Callback("D",new Continuation(2, "unlucky"), dispatcher));
    }
    static class Callback implements Runnable{
        String name;
        Continuation cont;
        ExecutorService pool;
        Callback(String name, Continuation cont, ExecutorService pool) {
            this.name = name;
            this.cont = cont;
            this.pool = pool;
        }
        public void run() {
            cont = luck(cont);
            System.out.println(name + ":" + cont.flag + " :" + cont.ret + " at " + Thread.currentThread().getName());
            if(!Objects.equals(cont.ret, "lucky")){
                pool.submit(this);
            }
        }
    }
    public record Continuation(int flag, String ret) {}
    private static Continuation luck(Continuation cont) {
        var flag = cont.flag % 7;
        return switch (flag) {
            case 0 -> new Continuation(1, cont.flag > 0 ? "lucky" : "unlucky");
            default -> new Continuation(flag + 1, "unlucky");
        };
    }
}