有時候有這樣的需求，需要多個線程執(zhí)行任務(wù)，每個線程都執(zhí)行不同的準(zhǔn)備工作，全部準(zhǔn)備好了，才能同時執(zhí)行下面的工作。這個怎么實現(xiàn)呢？

• 一是用CyclicBarrier （適用在多線程相互等待，直到到達(dá)一個屏障點。并且CyclicBarrier是可重用的。）實現(xiàn)。

代碼實現(xiàn)：

public class CyclicBarrierTest {
    boolean finalFlg = false;
    /**
     * CyclicBarrier 適用再多線程相互等待，直到到達(dá)一個屏障點。并且CyclicBarrier是可重用的。
     */
    CyclicBarrier cyclicBarrier = new CyclicBarrier(10);

    private void runThread() {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10; i++) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            executorService.submit(createThread(i));


        }
    }

    private Thread createThread(int i) {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    cyclicBarrier.await();
                    System.out.println("Thread:" + Thread.currentThread().getName() + "準(zhǔn)備完畢,time:" + System.currentTimeMillis());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }
        });
        thread.setName("name" + i);
        return thread;
    }

    public static void main(String[] args) {
        CyclicBarrierTest test = new CyclicBarrierTest();
        test.runThread();
    }
}

執(zhí)行結(jié)果：

Thread:pool-1-thread-10準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-1準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-3準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-2準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-7準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-6準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-5準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-4準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-9準(zhǔn)備完畢,time:1521037864652
Thread:pool-1-thread-8準(zhǔn)備完畢,time:1521037864652

從結(jié)果看，線程幾乎是同時執(zhí)行的

• 二是用CountDownLatch 實現(xiàn)，CountDownLatch可以理解為一個計數(shù)器，直到計數(shù)器為0了，等待的線程才執(zhí)行。

public class testCountDownLatch {
CountDownLatch countDownLatch = new CountDownLatch(1);
    private  void runThread(){
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for(int i=0;i<10 ;i++){
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            executorService.submit(new Runnable() {
                @Override
                public void run() {
                    try {
                        countDownLatch.await();
                        System.out.println("Thread:"+Thread.currentThread().getName()+",time: "+System.currentTimeMillis());
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        countDownLatch.countDown();
    }

    public static void main(String[] args) {
        testCountDownLatch test = new testCountDownLatch();
        test.runThread();
    }
}

從執(zhí)行結(jié)果看，線程也幾乎同時進(jìn)行的：

Thread:pool-1-thread-2,time: 1521038129807
Thread:pool-1-thread-3,time: 1521038129807
Thread:pool-1-thread-1,time: 1521038129807
Thread:pool-1-thread-4,time: 1521038129807
Thread:pool-1-thread-6,time: 1521038129807
Thread:pool-1-thread-5,time: 1521038129807
Thread:pool-1-thread-9,time: 1521038129807
Thread:pool-1-thread-8,time: 1521038129807
Thread:pool-1-thread-7,time: 1521038129807
Thread:pool-1-thread-10,time: 1521038129807

• 其他自己用wait和notify實現(xiàn)。

下一篇介紹下CyclicBarrier的用法。