1. 倒计时门闩
    2. 设定一个值，完成一个进行一次countDown，结束之后就开了（await的地方就能继续向下了）
    3. 门闩在那拴住门，不让他向下执行\
    4. 滚动发车===>坐满就走
    5. 与join实现的功能差不多
    6. 与join效率相比应该差不多===>但是一般这种阻塞的方法不谈效率===>运行的线程运行多长时间才应该算效率
    7. 门闩控制得比join灵活不少！！！（可以更加个性化）
    1. package com.mashibing.juc.c_020;
    3. import java.util.concurrent.CountDownLatch;
    5. public class T06_TestCountDownLatch {
    6.     public static void main(String[] args) {
    7.         usingJoin();
    8.         usingCountDownLatch();
    9.     }
    11.     private static void usingCountDownLatch() {
    12.         Thread[] threads = new Thread[100];
    13.         CountDownLatch latch = new CountDownLatch(threads.length);
    15.         for(int i=0; i<threads.length; i++) {
    16.             threads[i] = new Thread(()->{
    17.                 int result = 0;
    18.                 for(int j=0; j<10000; j++) result += j;
    19.                 latch.countDown();
    20.             });
    21.         }
    23.         for (int i = 0; i < threads.length; i++) {
    24.             threads[i].start();
    25.         }
    27.         try {
    28.             latch.await();
    29.         } catch (InterruptedException e) {
    30.             e.printStackTrace();
    31.         }
    33.         System.out.println("end latch");
    34.     }
    36.     private static void usingJoin() {
    37.         Thread[] threads = new Thread[100];
    39.         for(int i=0; i<threads.length; i++) {
    40.             threads[i] = new Thread(()->{
    41.                 int result = 0;
    42.                 for(int j=0; j<10000; j++) result += j;
    43.             });
    44.         }
    46.         for (int i = 0; i < threads.length; i++) {
    47.             threads[i].start();
    48.         }
    50.         for (int i = 0; i < threads.length; i++) {
    51.             try {
    52.                 threads[i].join();
    53.             } catch (InterruptedException e) {
    54.                 e.printStackTrace();
    55.             }
    56.         }
    58.         System.out.println("end join");
    59.     }
    60. }