java countDownLatch 线程辅助类，javacountdownlatch,countDownLat

java countDownLatch 线程辅助类，javacountdownlatch,countDownLat

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。```javaimport 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    }}

}```