countDownLatch 線程輔助類，是一個(gè)線程計(jì)數(shù)類，用來線程同步，每當(dāng)一個(gè)線程執(zhí)行完成后，就是加1，當(dāng)達(dá)到計(jì)數(shù)，就算執(zhí)行完成。初始值必須小于等于要執(zhí)行的線程數(shù)，為0 是，不其作用，大于0，小于等于線程數(shù)時(shí)，為同步線程數(shù)，當(dāng)大于線程數(shù)時(shí)，為死循環(huán)（可能不對(duì)）反正就是一直等待。粘貼上代碼，我也是粘貼別人的。自己手 敲一邊。實(shí)現(xiàn)機(jī)制沒看太懂，不過沒看到他同步里用鎖，代碼看到Unsafe，就進(jìn)不去了。

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，計(jì)數(shù)器減一
        }
    }
}

標(biāo)簽： 代碼

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