java多线程快速入门（二十一）

Posted 2021-01-22 cppdy

CountDownLatch（闭锁）计数器

　　有一个任务A，它要等待其他4个任务执行完毕之后才执行，此时就可以利用CountDownLatch来实现这种功能

package com.cppdy;

import java.util.concurrent.CountDownLatch;

class MyThread17 extends Thread{
    private CountDownLatch countdownlatch;
    
    public MyThread17(CountDownLatch countdownlatch) {
        this.countdownlatch=countdownlatch;
    }
    
    @Override
    public void run() {
        try {
            sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(getName()+"线程执行完毕");
        countdownlatch.countDown();
    }
}

public class ThreadDemo17 {

    public static void main(String[] args) throws Exception {
        CountDownLatch cd=new CountDownLatch(2);
        MyThread17 my1 = new MyThread17(cd);
        MyThread17 my2 = new MyThread17(cd);
        my1.start();
        my2.start();
        Thread.sleep(300);
        cd.await();
        System.out.println("主线程结束");
    }

}

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CyclicBarrier（回环栅栏）

　　CyclicBarrier初始化时规定一个数目，然后计算调用了CyclicBarrier.await()进入等待的线程数。当线程数达到这个数目时，所有进入等待状态的线程被唤醒并继续

package com.cppdy;

import java.util.concurrent.CyclicBarrier;

class MyThread18 extends Thread {
    private CyclicBarrier cyclicBarrier;

    public MyThread18(CyclicBarrier cyclicBarrier) {
        this.cyclicBarrier = cyclicBarrier;
    }

    @Override
    public void run() {
        System.out.println("开始执行线程");
        try {
            sleep(2000);
            //第一次进来，表示有一个线程等待，还不满足三个，不释放
            //第二次进来，也不满足
            //第三次进来，满足了，就继续执行下面的代码
            cyclicBarrier.await();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("结束执行线程");
    }
}

public class ThreadDemo18 {

    public static void main(String[] args) throws Exception {
        CyclicBarrier cb = new CyclicBarrier(3);
        MyThread18 my1 = new MyThread18(cb);
        MyThread18 my2 = new MyThread18(cb);
        MyThread18 my3 = new MyThread18(cb);
        my1.start();
        my2.start();
        my3.start();
        System.out.println("主线程执行结束");
    }

}

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Semaphore（信号量）

　　Semaphore是一种基于计数的信号量，它可以设置一个阀值，多个线程竞争获取许可信号，做自己的申请后归还，超过阀值后，线程申请许可信号将会被阻塞

package com.cppdy;

import java.util.Random;
import java.util.concurrent.Semaphore;

class MyThread19 extends Thread {
    private String name;
    private Semaphore sp;

    public MyThread19(String name, Semaphore sp) {
        this.name = name;
        this.sp = sp;
    }

    @Override
    public void run() {
        int availablePermits = sp.availablePermits();
        if (availablePermits > 0) {
            System.out.println(name + ",好开心啊，居然还有坑");
        } else {
            System.out.println(name + ",好伤心啊，怎么没有坑了");
        }
        try {
            sp.acquire();
            System.out.println(name + ",好开心啊，终于抢到啦");
            //模拟上厕所时间
            Thread.sleep(new Random().nextInt(1000));
            System.out.println(name + ",好爽啊，终于上完啦");
            sp.release();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class ThreadDemo19 {

    public static void main(String[] args) throws Exception {
        Semaphore sp = new Semaphore(3);
        for (int i = 0; i < 10; i++) {
            MyThread19 mt = new MyThread19("第" + i + "个人", sp);
            mt.start();
        }
    }

}

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