java多线程同步工具之CountDownlatch

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CountDownLatch犹如一个计数器，调用CountDownLatch对象的countDown()方法将计数器减一，当计数器到达0时，则所有等待者或单个等待者就开始执行，就好比：裁判一声令下，运动员同时开始奔跑，或者所有运动员都跑到了终点后裁判才可以公布结果。

案例：

public class CountdownLatchTest {public static void main(String[] args) {/*创建一个缓存型线程池*/ExecutorService service = Executors.newCachedThreadPool();/*创建一个计数器只有一个数*/final CountDownLatch cdOrder = new CountDownLatch(1);/*创建一个计数器，有3个计数器*/final CountDownLatch cdAnswer = new CountDownLatch(3);/*循环模拟3个线程*/for (int i = 0; i < 3; i++) {Runnable runnable = new Runnable() {public void run() {try {System.out.println("线程" + Thread.currentThread().getName() + "正准备接受命令");/*等待*/cdOrder.await();System.out.println("线程" + Thread.currentThread().getName() + "已接受命令");/*休眠*/Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() + "回应命令处理结果");/*计数器减一*/cdAnswer.countDown();} catch (Exception e) {e.printStackTrace();}}};service.execute(runnable);}try {/*休眠*/Thread.sleep((long) (Math.random() * 10000));System.out.println("线程" + Thread.currentThread().getName() + "即将发布命令");/*计数器减一*/cdOrder.countDown();System.out.println("线程" + Thread.currentThread().getName() + "已发送命令，正在等待结果");cdAnswer.await();System.out.println("线程" + Thread.currentThread().getName() + "已收到所有响应结果");} catch (Exception e) {e.printStackTrace();}service.shutdown();}}

程序运行结果：

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