Java Java类与示例

Phaser 的主要目的是使代表一个或多个活动阶段的线程能够同步。它允许我们定义一个同步对象，该对象等待特定阶段完成。然后它进入下一阶段，直到该阶段结束。它还可以用于同步单个阶段，在这方面，它的作用很像 CyclicBarrier。

类层次结构

java.lang.Object
  ? java.util.concurrent
    ? Class Phaser 

句法

public class Phaser
  extends Object

构造函数：

• Phaser() - 这将创建一个初始注册方为零的移相器。线程只有在注册后才能使用此移相器。

public Phaser()

• Phaser(intparty) ——这将创建一个相位器，它需要参与方的线程数才能进入下一阶段。

public Phaser(int parties)
throws IllegalArgumentException

• Phaser(Phaser parent) – 这指定了新对象的父移相器。注册方的数量设置为零。

public Phaser(Phaser parent)

• Phaser(Phaser parent, intparty) ——这为新创建的对象指定了一个父移相器，以及进入下一阶段所需的参与方数量。

public Phaser(Phaser parent, int parties)
throws IllegalArgumentException

示例 1：

注意：每次运行的输出可能会有所不同。

输出

Starting
Thread: B Phase Zero Started
Thread: A Phase Zero Started
Thread: C Phase Zero Started
Thread: A Phase One Started
Thread: B Phase One Started
Thread: C Phase One Started
Phase 0 Complete
Phase Zero Ended
Phase 1 Complete
Phase One Ended
Thread: C Phase Two Started
Thread: A Phase Two Started
Thread: B Phase Two Started
Phase 2 Complete
Phase Two Ended
Phaser is terminated

示例 2：

Java

// Java program to show Phaser Class
 
import java.util.concurrent.Phaser;
 
// A thread of execution that uses a phaser.
class MyThread implements Runnable {
    Phaser phaser;
    String title;
 
    public MyThread(Phaser phaser, String title)
    {
        this.phaser = phaser;
        this.title = title;
 
        phaser.register();
        new Thread(this).start();
    }
 
    @Override public void run()
    {
        System.out.println("Thread: " + title
                           + " Phase Zero Started");
        phaser.arriveAndAwaitAdvance();
 
        // Stop execution to prevent jumbled output
        try {
            Thread.sleep(10);
        }
        catch (InterruptedException e) {
            System.out.println(e);
        }
 
        System.out.println("Thread: " + title
                           + " Phase One Started");
        phaser.arriveAndAwaitAdvance();
 
        // Stop execution to prevent jumbled output
        try {
            Thread.sleep(10);
        }
        catch (InterruptedException e) {
            System.out.println(e);
        }
 
        System.out.println("Thread: " + title
                           + " Phase Two Started");
        phaser.arriveAndDeregister();
    }
}
 
public class PhaserExample {
    public static void main(String[] args)
    {
        Phaser phaser = new Phaser();
        phaser.register();
        int currentPhase;
 
        System.out.println("Starting");
 
        new MyThread(phaser, "A");
        new MyThread(phaser, "B");
        new MyThread(phaser, "C");
 
        // Wait for all threads to complete phase Zero.
        currentPhase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();
        System.out.println("Phase " + currentPhase
                           + " Complete");
        System.out.println("Phase Zero Ended");
 
        // Wait for all threads to complete phase One.
        currentPhase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();
        System.out.println("Phase " + currentPhase
                           + " Complete");
        System.out.println("Phase One Ended");
 
        currentPhase = phaser.getPhase();
        phaser.arriveAndAwaitAdvance();
        System.out.println("Phase " + currentPhase
                           + " Complete");
        System.out.println("Phase Two Ended");
 
        // Deregister the main thread.
        phaser.arriveAndDeregister();
        if (phaser.isTerminated()) {
            System.out.println("Phaser is terminated");
        }
    }
}

输出

Starting
Thread: C Phase Zero Started
Thread: A Phase Zero Started
Thread: B Phase Zero Started
Thread: B Phase One Started
Thread: C Phase One Started
Thread: A Phase One Started
Phase 0 Complete
Phase Zero Ended
Phase 1 Complete
Phase One Ended
Thread: A Phase Two Started
Thread: C Phase Two Started
Thread: B Phase Two Started
Phase 2 Complete
Phase Two Ended
Phaser is terminated

方法：

• int register() - 此方法用于在构建移相器后注册各方。它返回它注册到的阶段的阶段编号。

public int register()
throws IllegalArgumentException

• int reach() - 此方法表示线程已完成任务的某些部分。它不会暂停调用线程的执行。如果移相器已终止，则返回当前相位编号或负值。

public int arrive()
throws IllegalStateException

• int reachAndDeregister() – 此方法使线程能够到达一个阶段并自行取消注册，而无需等待其他线程到达。如果移相器已终止，则返回当前相位编号或负值。

public int arriveAndDeregister()
throws IllegalStateException

• int reachAndAwaitAdvance() - 该方法在一个阶段暂停线程的执行，以等待其他线程。如果移相器已终止，则返回当前相位编号或负值。

public int arriveAndAwaitAdvance()
throws IllegalStateException

• final int getPhase() - 此方法返回当前阶段编号。如果调用移相器终止，则返回负值。

public final int getPhase() 

• boolean onAdvance(int phase, intparty) - 此方法有助于定义阶段推进应如何发生。为此，用户必须重写此方法。要终止移相器，onAdvance() 方法返回 true，否则返回 false；

protected boolean onAdvance(int phase, int parties)

演示 Phaser 类的方法的示例——其中方法被覆盖，以便移相器仅执行指定数量的阶段。

Java

// Java program to demonstrate
// the methods of Phaser class
 
import java.util.concurrent.Phaser;
 
// Extend MyPhaser and override onAdvance()
// so that only specific number of phases
// are executed
class MyPhaser extends Phaser {
    int numPhases;
    MyPhaser(int parties, int phaseCount)
    {
        super(parties);
        numPhases = phaseCount - 1;
    }
 
    @Override
    protected boolean onAdvance(int phase,
                                int registeredParties)
    {
        System.out.println("Phase " + phase
                           + " completed.\n");
 
        // If all phases have completed, return true.
        if (phase == numPhases || registeredParties == 0) {
            return true;
        }
 
        // otherwise, return false
        return false;
    }
}
 
// A thread of execution that uses a phaser
class ModifiedThread implements Runnable {
    Phaser phsr;
    String name;
 
    ModifiedThread(Phaser p, String n)
    {
        phsr = p;
        name = n;
        phsr.register();
        new Thread(this).start();
    }
 
    @Override public void run()
    {
        while (!phsr.isTerminated()) {
            System.out.println("Thread " + name
                               + " Beginning Phase "
                               + phsr.getPhase());
            phsr.arriveAndAwaitAdvance();
 
            try {
                Thread.sleep(10);
            }
            catch (InterruptedException e) {
                System.out.println(e);
            }
        }
    }
}
 
public class PhaserExample2 {
    public static void main(String[] args)
    {
        MyPhaser phsr = new MyPhaser(1, 4);
        System.out.println("Starting");
 
        new ModifiedThread(phsr, "A");
        new ModifiedThread(phsr, "B");
        new ModifiedThread(phsr, "C");
 
        while (!phsr.isTerminated()) {
            phsr.arriveAndAwaitAdvance();
        }
        System.out.println("The phaser is terminated\n");
    }
}

输出

Starting
Thread B Beginning Phase 0
Thread C Beginning Phase 0
Thread A Beginning Phase 0
Phase 0 completed.

Thread A Beginning Phase 1
Thread B Beginning Phase 1
Thread C Beginning Phase 1
Phase 1 completed.

Thread C Beginning Phase 2
Thread A Beginning Phase 2
Thread B Beginning Phase 2
Phase 2 completed.

Thread A Beginning Phase 3
Thread B Beginning Phase 3
Thread C Beginning Phase 3
Phase 3 completed.

The phaser is terminated

参考： https://docs.oracle.com/javase/9/docs/api/ Java/util/concurrent/Phaser.html