JUC-CountDownLatch与多线程的应用

叁歲伎倆 2022-09-15 05:51 183阅读 0赞

public class CountDownLatchDemo {
        private static AtomicInteger a = new AtomicInteger();
    
        public static void main(String[] args) {
            int count = 50;
            for (int i = 0; i < count; i++) {
                new Thread(()->{
                    for (int j = 0; j < 1000; j++) {
                        a.getAndIncrement();
                    }
                }).start();
            }
    
            System.out.println(a.get());
        }
    }

这段代码我们理想的结果得到50000，但是main线程跑的太快，thread线程执行太耗时，结果小于5000

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5Yqq5Yqb5aWL5paXR08_size_13_color_FFFFFF_t_70_g_se_x_16][]

可以让main线程睡眠来等待thread线程执行完，但是这种做法不精确，此时可以使用CountDownLatch解决

public class CountDownLatchDemo {
        private static AtomicInteger a = new AtomicInteger();
    
        public static void main(String[] args) throws InterruptedException {
            int count = 50;
            CountDownLatch countDownLatch = new CountDownLatch(count);
            for (int i = 0; i < count; i++) {
                new Thread(()->{
                    try {
                        for (int j = 0; j < 1000; j++) {
                            a.getAndIncrement();
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    } finally {
                        countDownLatch.countDown();
                    }
                }).start();
            }
    //        try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); };
            countDownLatch.await(); // 通过await()阻塞main线程，直到thread线程全部执行完
            System.out.println(a.get());
        }
    }

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