CountDownLatch-等待一个线程池执行完所有线程

• 创建一个线程池 threadPoolExecutor 线程数量为threadCount，
• 执行methodA()方法，threadCount次
• 等待线程池的线程全部执行完，即latch为0
• shutdown()线程池

    @Test
    public void test(int threadCount) {
        ExecutorService threadPoolExecutor = new ThreadPoolExecutor(
　　　　　　　　　 threadCount/2, 
　　　　　　　　　 threadCount,
                1L, TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(threadCount),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());

        CountDownLatch latch = new CountDownLatch(threadCount);

        //循环执行methodA()方法
        for (int count = threadCount; count > 0; count--) {
            threadPoolExecutor.submit(() -> {
                try {
                    methodA( );
                } catch (Exception e) {
                    log.error(e.getMessage(), e);
                } finally {
                    latch.countDown();
                }
            });
        }

        //阻塞当前主线程，直到latch等于0
        try {
            //阻塞当前线程，直到计数器的值为0
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //关闭线程池
        threadPoolExecutor.shutdown();
    }