CountDownLatch使用

比眉伴天荒 2021-09-30 02:30 322阅读 0赞

CountDownLatch 类位于java.util.concurrent包下，利用它可以实现类似计数器的功能。比如有一个任务A，它要等待其他4个任务执行完毕之后才能执行，此时就可以利用CountDownLatch来实现这种功能了。CountDownLatch是通过一个计数器来实现的，计数器的初始值为线程的数量。每当一个线程完成了自己的任务后，计数器的值就会减1。当计数器值到达0时，它表示所有的线程已经完成了任务，然后在闭锁上等待的线程就可以恢复执行任务。

package 线程池;
    
    import java.util.concurrent.CountDownLatch;
    
    public class T1 {
    
        public static void main(String[] args) {
            CountDownLatch countDownLatch = new CountDownLatch(2);
            new Thread(new Runnable() {
                @Override
                public void run() {
                    System.out.println(Thread.currentThread().getName() + ",子线程开始执行...");
                    countDownLatch.countDown();
                    System.out.println(Thread.currentThread().getName() + ",子线程结束执行...");
                }
            }).start();
    
            new Thread(new Runnable() {
    
                @Override
                public void run() {
                    System.out.println(Thread.currentThread().getName() + ",子线程开始执行...");
                    countDownLatch.countDown();//计数器值每次减去1
                    System.out.println(Thread.currentThread().getName() + ",子线程结束执行...");
                }
            }).start();
    
            try {
                countDownLatch.await();// 減去为0,恢复任务继续执行
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("两个子线程执行完毕....");
            System.out.println("主线程继续执行.....");
            for (int i = 0; i <10; i++) {
                System.out.println("main,i:"+i);
            }
        }
    }

结果：

D:\Application\Java\jdk1.8.0_201\bin\java.exe "-javaagent:D:\Application\IntelliJ IDEA 2018.3.4\lib\idea_rt.jar=54703:D:\Application\IntelliJ IDEA 2018.3.4\bin" -Dfile.encoding=UTF-8 -classpath D:\Application\Java\jdk1.8.0_201\jre\lib\charsets.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\deploy.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\javaws.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\jce.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\jfr.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\jsse.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\management-agent.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\plugin.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\resources.jar;D:\Application\Java\jdk1.8.0_201\jre\lib\rt.jar;D:\Workspace\flutter\jgs\target\classes 线程池.T1
    Thread-0,子线程开始执行...
    Thread-0,子线程结束执行...
    Thread-1,子线程开始执行...
    Thread-1,子线程结束执行...
    两个子线程执行完毕....
    主线程继续执行.....
    main,i:0
    main,i:1
    main,i:2
    main,i:3
    main,i:4
    main,i:5
    main,i:6
    main,i:7
    main,i:8
    main,i:9
    
    Process finished with exit code 0