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java countDownLatch 线程辅助类

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countDownLatch线程辅助类,是一个线程计数类,用来线程同步,每当一个线程执行完成后,就是加1,当达到计数,就算执行完成。初始值必须小于等于要执行的线程数,为0是,不其作用,大于0,小于等于线程数时,为同步线程数,当大于线程数时,为死循环(可能不对)反正就是一直等待。粘贴上代码,我也是粘贴别人的。自己手敲一边。实现机制没看太懂,不过没看到他同步里用锁,代码看到Unsafe,就进不去了。```java import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.CountDownLatch;

public class T1 { final static SimpleDateFormat sdf = new SimpleDateFormat( "yyyy-MM-dd HH:mm:ss");

public static void main(String[] args) throws Exception {
    CountDownLatch countDownLatch = new CountDownLatch(3);
    Worker w1 = new Worker("w1", 2000, countDownLatch);
    Worker w2 = new Worker("w2", 5000, countDownLatch);
    w1.start();//
    w2.start();//
    countDownLatch.await();// 等待所有工人完成工作
    System.out.println("all work done at " + sdf.format(new Date()));
}

static class Worker extends Thread {
    String workerName;
    int workTime;
    CountDownLatch latch;

    public Worker(String workerName, int workTime, CountDownLatch latch) {
        this.workerName = workerName;
        this.workTime = workTime;
        this.latch = latch;
    }

    @Override
    public void run() {
        System.out.println("Worker " + workerName + " do work begin at "
                + sdf.format(new Date()));
        try {
            Thread.sleep(workTime);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Worker " + workerName + " do work complete at "
                + sdf.format(new Date()));
        latch.countDown();// 工人完成工作,计数器减一
    }
}

} ```

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