CountDownLatch

使用原理

1. 创建CountDownLatch并设置计数器值。

2. 启动多线程并且调用CountDownLatch实例的countDown()方法。

3. 主线程调用 await() 方法，这样主线程的操作就会在这个方法上阻塞，直到其他线程完成各自的任务，count值为0，停止阻塞，主线程继续执行。

使用模板

public class CountDownLatchTest {

    /**
     * a start signal that prevents any worker from proceeding
     * until the driver is ready for them to proceed;
     * @param args
     * @throws InterruptedException
     */
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch startSignal = new CountDownLatch(1);
        CountDownLatch doneSignal = new CountDownLatch(10);
        for (int i = 0; i < 10; i++) {
            // create and start threads
            new Thread(new Worker(startSignal, doneSignal)).start();
        }
        // don't let run yet
        System.out.println("do something else 1");
        // let all threads proceed
        startSignal.countDown();
        System.out.println("do something else 2");
        // wait for all to finish
        doneSignal.await();
        System.out.println("wait for all to finsh");
    }

    static class Worker implements Runnable{

        private final CountDownLatch startSignal;
        private final CountDownLatch doneSignal;

        Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
            this.startSignal = startSignal;
            this.doneSignal = doneSignal;
        }

        @Override
        public void run() {
            try {
                startSignal.await();
                doWork();
                doneSignal.countDown();
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }

        void doWork() {
            System.out.println("do work!");
        }
    }

}

引用地址： Java—CountDownLatch使用详解