对于CountDownLatch和CyclicBarrier使用场景的理解

一.CountDownLatch
1：多个线程等待某个线程执行完成时再开始执行，如果用一条黑线表示一个线程的话，如下图：

2：某个线程等待多个线程执行完成时再开始执行，如果用一条黑线表示一个线程的话，如下图：

二.CyclicBarrier

  多个线程都完成各自指定逻辑的时候再继续执行剩余逻辑

示例1：

    private static void oneWaitMore() throws InterruptedException {
        final CountDownLatch countDownLatch=new CountDownLatch(4);
        for (int i = 0; i < 5; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    System.out.println("hello");
                    countDownLatch.countDown();
                }
            }).start();
        }
        countDownLatch.await();
        System.out.println("world");

    }

结果1：

hello
hello
hello
hello
hello
world

 

 

示例2：

   private static void moreWaitone (){
        final CountDownLatch countDownLatch=new CountDownLatch(1);
        for (int i = 0; i < 5; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        countDownLatch.await();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("world");
                }
            }).start();
        }
        System.out.println("hello");
        countDownLatch.countDown();
    }

结果2：

hello
world
world
world
world
world

 

 

示例3：

    private static void cyclicBarrierTest() {
        final CyclicBarrier cyclicBarrier = new CyclicBarrier(5);
        for (int i = 0; i < 5; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    System.out.println("hello");
                    try {
                        cyclicBarrier.await();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } catch (BrokenBarrierException e) {
                        e.printStackTrace();
                    }
                    System.out.println("world");

                }
            }).start();
        }
    }

结果3：

hello
hello
hello
hello
hello
world
world
world
world
world