多线程 并发工具类CountDownLatch

方法及解释 public CountDownLatch(int count)参数传递线程数，表示等待线程数量 public void await()让线程等待 public void countDown()当前线程执行完毕 使用场景 让某一条线程等待其他线程执行完毕之后再执行

利用案例加深印象: 利用CountDownLatch创建对象管理3个线程 通过第4个线程完成收尾动作

代码实现:(一个妈妈收尾和三个小孩吃饺子的案例) //测试类:

public class countdownLatchdemo {
    public static void main(String[] args) {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        mothercountdown mo = new mothercountdown(countDownLatch);
        mo.start();
        child1 c1 = new child1(countDownLatch);
        c1.setName("小明");
        child2 c2 = new child2(countDownLatch);
        c2.setName("小刚");
        child3 c3 = new child3(countDownLatch);
        c3.setName("小红");
        c1.start();
        c2.start();
        c3.start();
    }
}

//妈妈类:

public class mothercountdown extends  Thread{
    private  CountDownLatch countDownLatch;
    public mothercountdown(CountDownLatch countDownLatch) {
        this.countDownLatch=countDownLatch;
    }

    @Override
    public void run() {
        //等待孩子吃完
        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //收拾碗筷
        System.out.println("妈妈去收拾碗筷");
    }
}

//分别是3个小娃娃类:

public class child1 extends  Thread{
    private  CountDownLatch countDownLatch;
    public child1(CountDownLatch countDownLatch) {
        this.countDownLatch=countDownLatch;
    }

    @Override
    public void run() {
        for (int i = 1; i <= 10; i++) {
            //吃饺子
            System.out.println(getName()+"正在吃第"+i+"饺子");
        }
        //吃完说一声
        countDownLatch.countDown();
    }
}

public class child2 extends  Thread{
    private  CountDownLatch countDownLatch;
    public child2(CountDownLatch countDownLatch) {
        this.countDownLatch=countDownLatch;
    }

    @Override
    public void run() {
        for (int i = 1; i <= 15; i++) {
            //吃饺子
            System.out.println(getName()+"正在吃第"+i+"饺子");
        }
        //吃完说一声
        countDownLatch.countDown();
    }
}

public class child3 extends  Thread{
    private  CountDownLatch countDownLatch;
    public child3(CountDownLatch countDownLatch) {
        this.countDownLatch=countDownLatch;
    }

    @Override
    public void run() {
        for (int i = 1; i <= 20; i++) {
            //吃饺子
            System.out.println(getName()+"正在吃第"+i+"饺子");
        }
        //吃完说一声
        countDownLatch.countDown();
    }
}

个人小结:

​ 1. CountDownLatch(int count)：参数写等待线程的数量。并定义了一个计数器。

​ 2. await()：让线程等待，当计数器为0时，会唤醒等待的线程

​ 3. countDown()： 线程执行完毕时调用，会将计数器-1。