阶段终止后的 java.util.concurrent.Phaser 回调

Question

我调查了 java.util.concurrent 包中的 Phaser 并编写了代码示例:

public class ThreadsApp {

    public static void main(String[] args) {

        Phaser phaser = new Phaser(1);
        new Thread(new PhaseThread(phaser, "PhaseThread 1")).start();
        new Thread(new PhaseThread(phaser, "PhaseThread 2")).start();

        // ждем завершения фазы 0
        int phase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();
        System.out.println("phase " + phase + " finished");
        // ждем завершения фазы 1
        phase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();
        System.out.println("phase " + phase + " finished");

        // ждем завершения фазы 2
        phase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();
        System.out.println("phase " + phase + " finished");

        phaser.arriveAndDeregister();
    }
}

class PhaseThread implements Runnable {

    Phaser phaser;
    String name;

    PhaseThread(Phaser p, String n) {

        this.phaser = p;
        this.name = n;
        phaser.register();
    }

    public void run() {
        try {
            System.out.println(name + " start execute phase " + phaser.getPhase());
            Thread.sleep(1000);
            phaser.arriveAndAwaitAdvance(); // сообщаем, что первая фаза достигнута

            System.out.println(name + " start execute phase " + phaser.getPhase());
            Thread.sleep(2000);
            phaser.arriveAndAwaitAdvance(); // сообщаем, что вторая фаза достигнута

            System.out.println(name + " start execute phase " + phaser.getPhase());
            Thread.sleep(3000);
            phaser.arriveAndDeregister(); // сообщаем о завершении фаз и удаляем с регистрации объекты

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

输出:

PhaseThread 2 start execute phase 0
PhaseThread 1 start execute phase 0
PhaseThread 2 start execute phase 1
phase 0 finished
PhaseThread 1 start execute phase 1
phase 1 finished
PhaseThread 1 start execute phase 2
PhaseThread 2 start execute phase 2
phase 2 finished

输出与我想要的有点不同:

我想要:

PhaseThread 2 start execute phase 0
PhaseThread 1 start execute phase 0
phase 0 finished
PhaseThread 2 start execute phase 1
PhaseThread 1 start execute phase 1
phase 1 finished
PhaseThread 1 start execute phase 2
PhaseThread 2 start execute phase 2
phase 2 finished

因此，我希望 phase X finish 将在 PhaseThread # startexecute stage X 和 strict before PhaseThread strict after 之间打印# 开始执行阶段X+1

我明白为什么我的代码工作不正常，但我不知道如何实现所需的行为。我认为这是可能的，因为到处都写有 Phaser 涵盖 CyclicBarrier 功能。

Answer 1

阅读 Phaser 的 Java 文档显示了一个名为 onAdvance 的重写方法，该方法可用于在阶段实际完成时打印 X 阶段完成。只需修改如下代码即可。

public class ThreadsApp {

    public static void main(String[] args) {

        Phaser phaser = new Phaser(1) {
            protected boolean onAdvance(int phase, int parties) { 
                System.out.println("phase " + phase + " finished");
                return false; 
            }
        };
        new Thread(new PhaseThread(phaser, "PhaseThread 1")).start();
        new Thread(new PhaseThread(phaser, "PhaseThread 2")).start();

        // ждем завершения фазы 0
        int phase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();

        // ждем завершения фазы 1
        phase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();


        // ждем завершения фазы 2
        phase = phaser.getPhase();
        phaser.arriveAndDeregister();
    }
}

class PhaseThread implements Runnable {

    Phaser phaser;
    String name;

    PhaseThread(Phaser p, String n) {

        this.phaser = p;
        this.name = n;
        phaser.register();
    }

    public void run() {
        try {
            System.out.println(name + " start execute phase " + phaser.getPhase());
            Thread.sleep(1000);
            phaser.arriveAndAwaitAdvance(); // сообщаем, что первая фаза достигнута

            System.out.println(name + " start execute phase " + phaser.getPhase());
            Thread.sleep(2000);
            phaser.arriveAndAwaitAdvance(); // сообщаем, что вторая фаза достигнута

            System.out.println(name + " start execute phase " + phaser.getPhase());
            Thread.sleep(3000);
            phaser.arriveAndDeregister(); // сообщаем о завершении фаз и удаляем с регистрации объекты

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}