Java 并发编程（三）Phaser

news2024/12/26 11:54:46

#Phaser

功能介绍

CyclicBarrier 解决了 CountDownLatch的缺点，但是其本身也仍然具备一定的缺陷，比如不可以动态添加parties 调用一次await 仅占用1个parties

public class MyPhaser {

    private Phaser phaser = new Phaser(3);

    public void testA(){
        System.out.println(Thread.currentThread().getName() + " 1Begin " + System.currentTimeMillis());
        phaser.arriveAndAwaitAdvance();
        System.out.println(Thread.currentThread().getName() + " 1End " + System.currentTimeMillis());


        System.out.println(Thread.currentThread().getName() + " 2Begin " + System.currentTimeMillis());
        phaser.arriveAndAwaitAdvance();
        System.out.println(Thread.currentThread().getName() + " 2End " + System.currentTimeMillis());

    }

    public void testB(){
        try {
            System.out.println(Thread.currentThread().getName() + " 1Begin " + System.currentTimeMillis());
            Thread.sleep(5000);
            phaser.arriveAndAwaitAdvance();
            System.out.println(Thread.currentThread().getName() + " 1End " + System.currentTimeMillis());

            System.out.println(Thread.currentThread().getName() + " 2Begin " + System.currentTimeMillis());
            Thread.sleep(5000);
            phaser.arriveAndAwaitAdvance();
            System.out.println(Thread.currentThread().getName() + " 2End " + System.currentTimeMillis());

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

    public static void main(String[] args) {
        MyPhaser myPhaser = new MyPhaser();
        MyThread myThread = new MyThread(myPhaser);
        myThread.setName("A");
        myThread.start();

        MyThread myThread1 = new MyThread(myPhaser);
        myThread1.setName("B");
        myThread1.start();

        MyThreadC myThread2 = new MyThreadC(myPhaser);
        myThread2.setName("C");
        myThread2.start();

    }

    @AllArgsConstructor
    @NoArgsConstructor
    @Data
    public static class MyThread extends Thread{

        private MyPhaser myPhaser;
        @Override
        public void run() {
            myPhaser.testA();
        }
    }

    @AllArgsConstructor
    @NoArgsConstructor
    @Data
    public static class MyThreadC extends Thread{

        private MyPhaser myPhaser;
        @Override
        public void run() {
            myPhaser.testB();
        }
    }

}

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使用 arriveAndAwaitAdvance方法再遇到计数不足时会导致进程被阻塞可以使用 arriveAndDeregister 在线程结束时使partie减一。

只需改动下 testB方法即可验证

    public void testB(){
        try {
            System.out.println(Thread.currentThread().getName() + " 1Begin " + System.currentTimeMillis());
            Thread.sleep(5000);
            phaser.arriveAndAwaitAdvance();
            System.out.println(Thread.currentThread().getName() + " 1End " + System.currentTimeMillis());

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

getPhase() 可以获取当前已经到达多少个屏障

在通过新的屏障时被调用 onAdvance
返回true不等待了， Phaser 为无效/销毁状态
返回false Phaser 继续工作

    private Phaser phaser = new Phaser(3){
        @Override
        protected boolean onAdvance(int phase, int registeredParties) {
            System.out.println(phase + " " + registeredParties);
            System.out.println("onAdvance used");
            //返回true不等待了， Phaser 为无效/销毁状态
            //返回false Phaser 继续工作
            return true;
        }
    };

getRegisteredParties() 获取注册的parties
register() 动态添加一个parties
bulkRegister(n) 动态批量添加 parties
getArrivedParties() 获取已经被使用的parties
getUnarrivedParties() 获取未使用的parties
arrive() 使parties值加1，但不再屏障处等待，继续向下运行。
Pharse 也具备计数重制功能

public static void main(String[] args) {
        Phaser phaser = new Phaser(2);
        System.out.println(1 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();

        System.out.println(2 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();

        System.out.println(3 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();

        System.out.println(4 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();

        System.out.println(5 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();
    }

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如上，每次调用arrive() getArrivedParties+1 切每次达到2 都会重制计数

awaitAdvance(n) 如果 n == getPhase 则阻塞且不可被 interrupted

    public static void main(String[] args) {
        Phaser phaser = new Phaser(2);
        System.out.println(1 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();
        phaser.awaitAdvance(0);
        System.out.println("run");
        System.out.println(2 + " getPhase: " + phaser.getPhase() + " getArrivedParties: " + phaser.getArrivedParties() );
        phaser.arrive();
    }

2 并未执行
在这里插入图片描述

awaitAdvanceInterruptibly() 与 awaitAdvance() 相反可以被中断。
awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit) 当屏障达到 phase时如果超过 timeout 时间没有变化测抛出异常
forceTermination() 将屏障取消并且 getPhase = Integer.MIN_VALUE
isTerminated() 判断Phase 是否已经被销毁