java - 将线程注册到 Phaser

标签 java multithreading concurrency java.util.concurrent phaser

我正在学习 Phaser。在这样做的过程中,我遇到了一个问题。下面是我的代码,

public class RunnableTask implements Runnable {

    private Phaser phaser;

    public RunnableTask(Phaser phaser) {
        this.phaser = phaser;
        this.phaser.register();  // Question
    }

    @Override
    public void run() {
        // this.phaser.register();  // Question
        print("After register");
        for (int i = 0; i < 2; i++) {
            sleep();
            print("Before await" + i + ":");
            this.phaser.arriveAndAwaitAdvance();
            print("After advance" + i + ":");
        }
    }

    private void sleep() {
        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void print(String msg) {

        System.out.println(String.format("%s: %s, time=%s, registered=%s, arrived=%s, unarrived=%s, phase=%s.", msg,
                Thread.currentThread().getName(), LocalTime.now(), this.phaser.getRegisteredParties(),
                this.phaser.getArrivedParties(), this.phaser.getUnarrivedParties(), this.phaser.getPhase()));
    }

 }

上述示例测试

public class TestPhaser {

    public static void main(String[] args) {

        Phaser phaser = new Phaser();

        RunnableTask task = new RunnableTask(phaser);

        Thread t1 = new Thread(task, "t1");
        Thread t2 = new Thread(task, "t2");
        Thread t3 = new Thread(task, "t3");

        t1.start();
        t2.start();
        t3.start();
    } 
}

执行上述程序后,输出为:

After register: t3, time=22:01:26.636, registered=1, arrived=0, unarrived=1, phase=0.

After register: t2, time=22:01:26.636, registered=1, arrived=0, unarrived=1, phase=0.

After register: t1, time=22:01:26.636, registered=1, arrived=0, unarrived=1, phase=0.

Before await 0:: t3, time=22:01:28.728, registered=1, arrived=0, unarrived=1, phase=0.

Before await 0:: t2, time=22:01:28.728, registered=1, arrived=0, unarrived=1, phase=0.

Before await 0:: t1, time=22:01:28.728, registered=1, arrived=0, unarrived=1, phase=0.

After advance 0:: t1, time=22:01:28.728, registered=1, arrived=0, unarrived=1, phase=3.

After advance 0:: t2, time=22:01:28.728, registered=1, arrived=0, unarrived=1, phase=3.

After advance 0:: t3, time=22:01:28.729, registered=1, arrived=0, unarrived=1, phase=3.

Before await 1:: t2, time=22:01:30.730, registered=1, arrived=0, unarrived=1, phase=3.

Before await 1:: t3, time=22:01:30.730, registered=1, arrived=0, unarrived=1, phase=3.

After advance 1:: t2, time=22:01:30.730, registered=1, arrived=0, unarrived=1, phase=4.

After advance 1:: t3, time=22:01:30.732, registered=1, arrived=0, unarrived=1, phase=5.

Before await 1:: t1, time=22:01:30.730, registered=1, arrived=0, unarrived=1, phase=3.

After advance 1:: t1, time=22:01:30.732, registered=1, arrived=0, unarrived=1, phase=6.

您可以看到这里有很多差异。线程不按顺序前进。此外,有几个阶段缺失或/且不按顺序排列。

当我将代码行 this.phaser.register() 从构造函数移动到 run 方法的开头时,输出为:

After register: t1, time=22:10:58.230, registered=3, arrived=0, unarrived=3, phase=0.

After register: t3, time=22:10:58.230, registered=3, arrived=0, unarrived=3, phase=0.

After register: t2, time=22:10:58.230, registered=3, arrived=0, unarrived=3, phase=0.

Before await 0:: t2, time=22:11:00.314, registered=3, arrived=0, unarrived=3, phase=0.

Before await 0:: t1, time=22:11:00.314, registered=3, arrived=0, unarrived=3, phase=0.

Before await 0:: t3, time=22:11:00.314, registered=3, arrived=0, unarrived=3, phase=0.

After advance 0:: t2, time=22:11:00.315, registered=3, arrived=0, unarrived=3, phase=1.

After advance 0:: t3, time=22:11:00.315, registered=3, arrived=0, unarrived=3, phase=1.

After advance 0:: t1, time=22:11:00.315, registered=3, arrived=0, unarrived=3, phase=1.

Before await 1:: t1, time=22:11:02.319, registered=3, arrived=0, unarrived=3, phase=1.

Before await 1:: t2, time=22:11:02.319, registered=3, arrived=0, unarrived=3, phase=1.

Before await 1:: t3, time=22:11:02.319, registered=3, arrived=0, unarrived=3, phase=1.

After advance 1:: t3, time=22:11:02.320, registered=3, arrived=0, unarrived=3, phase=2.

After advance 1:: t2, time=22:11:02.320, registered=3, arrived=0, unarrived=3, phase=2.

After advance 1:: t1, time=22:11:02.321, registered=3, arrived=0, unarrived=3, phase=2.

线程执行和阶段按顺序排列看起来要好得多。

这是我的问题:

1)为什么在Runnable的构造函数中注册各方时会出现很多差异?

2) 在第二个结果中,每个阶段到达和未到达的统计数据均为零(不正确)。那么,如何获得它们的正确数字呢?

感谢任何帮助。

最佳答案

在第一个示例“在构造函数中创建 Phaser”中,您仅向 Phaser 注册一个线程。您必须创建三个任务,才能在 Phaser 中注册三个线程。

这样修改代码,就可以了。 (不要忘记从代码中删除初始 RunnableTask task = new RunnableTask(phaser); )

    Thread t1 = new Thread(new RunnableTask(phaser), "t1");
    Thread t2 = new Thread(new RunnableTask(phaser), "t2");
    Thread t3 = new Thread(new RunnableTask(phaser), "t3");

在第二个示例中,您在所有线程中等待了 2 秒,这是准确的,所有线程几乎同时到达并等待,像这样更改您的 sleep 方法以引入一些不同的等待,以便线程看到一些到达和未到达线程

  private void sleep() {
    try {
      Random r = new Random();    
      TimeUnit.SECONDS.sleep(r.nextInt(5));
    } catch(InterruptedException e) {
      e.printStackTrace();
    }
  }

你的第二个例子有效,但它不正确。它有效只是因为你在 run 方法开始时有 sleep ,所以所有线程在你调用 Phaser 上的到达和提前方法之前都 catch 在 Phaser 中注册。 如果您要删除 sleep ,那么在调用此线路后

t1.start();

T1 run 方法将被运行,并且 t1 线程将被注册到移相器中。那么可能会在线程 t2 和 t3 启动并注册到移相器中之前调用 t1 run 方法中的 this.phaser.arriveAndAwaitAdvance() ,因此移相器不会等待它们。

您应该在任务的构造函数中或在启动线程之前调用的方法中注册到phaser。

关于java - 将线程注册到 Phaser,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/53474375/

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