CountDownLatch:不调用await()方法 来控制线程并发

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * CountDownLatch:多线程控制工具类，不调用await()方法 来控制线程并发
 */
public class CountDownLatchDemo {
 
    //实例化并指定计数个数
    private  static CountDownLatch countDown = new CountDownLatch(1);
 
    public static Runnable r1 = new Runnable(){
        @Override
        public void run() {
            try{
                Thread.sleep(8000);
                System.out.println("r1 run");
                countDown.countDown();//个数-1
            }catch (Exception e){
                e.printStackTrace();
            }
 
        }
    };
 
   public static Runnable r2 = new Runnable() {
        @Override
        public void run() {
            try{
                Thread.sleep(3000);
                System.out.println("r2 run");
                countDown.countDown();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    };
 
    public  static Runnable r3 = new Runnable() {
        @Override
        public void run() {
            try{
                Thread.sleep(5000);
                System.out.println("r3 run");
                countDown.countDown();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    };
 
    public static void main(String[] args) throws  Exception{
        System.out.println("===begin=====");
        ExecutorService exec = Executors.newFixedThreadPool(3);
        exec.submit(r1);
        exec.submit(r2);
        exec.submit(r3);
 
        //等待检查，等待三个线程都执行完成后，主线程才能继续执行
//        countDown.await();
 
        System.out.println("====end=====");
        exec.shutdown();
    }
}

输出结果:1个1个等待输出的 由此可见控制住了线程的并发

===begin=====
====end=====
r2 run
r3 run
r1 run