1.countDownLatch

阻塞，countDown到零，结束阻塞继续执行。可以时一个线程countDown，可以是多个线程countDown

public static void usingCountDownLatch(){
        Thread[] threads = new Thread[100];
        CountDownLatch latch = new CountDownLatch(threads.length);

        for (int i = 0; i < threads.length; i++){
            threads[i] = new Thread(() -> {
               int result = 0;
               for (int j =  0; j<10000; j++) result += j;
               latch.countDown();
            });
        }

        for (int i = 0; i< threads.length; i++){
            threads[i].start();
        }

        try{
            latch.await();  //阻塞，当countDown为0时，阻塞放开。 所有运行线程结束了，才结束阻塞
        }catch (InterruptedException e){
            e.printStackTrace();
        }
    }

2.CyclicBarrier

阻塞n个线程，数量达到了继续执行

public static void main(String[] args) {
        //参数：parties:满多少人，new Runnable 要执行的任务
        CyclicBarrier barrier = new CyclicBarrier(20, new Runnable() {
            @Override
            public void run() {
                System.out.println("满人，发车。 let's go");
            }
        });

        //不同的写法
        CyclicBarrier b = new CyclicBarrier(20);
        CyclicBarrier b1 = new CyclicBarrier(20, ()->{
            System.out.println("let's go");
        });

        for (int i = 0; i< 100; i++){
            new Thread(() -> {
                try{
                    barrier.await();
                }catch (InterruptedException e){
                    e.printStackTrace();
                }catch (BrokenBarrierException e){
                    e.printStackTrace();
                }
            }).start();
        }
    }