[闭锁]同步工具类 CountDownLatch 的使用

Love The Way You Lie 2022-06-09 01:20 165阅读 0赞

CountDownLatch 在使用中，计数器初始化为一个正数，表示需要等待的一组事件的数量。countDown表示有一个事件已经发生了，而await方法等待计数器达到零，表示所有的事件都已经发生。如果计数器非零，那么await会一直阻塞直到计数器为零，或者等待中的线程中断，或者等待超时。

package demo.java.util.concurrent;
    
    
    import java.util.Date;
    import java.util.concurrent.CountDownLatch;
    
    /**
     * 只有当完成了job1 和 job2 作业后,才执行job3
     * Created by yuyufeng on 2017/8/24.
     */
    public class CountDownLatchTest {
        public static void main(String[] args) throws InterruptedException {
            long beginTime = System.currentTimeMillis();
            CountDownLatch countDownLatch = new CountDownLatch(2); //因为job1 job2共两个线程,所以计数2
            new Job("job1", 3000, countDownLatch).start();
            new Job("job2", 5000, countDownLatch).start();
            countDownLatch.await();
            System.out.println("do job3...");
            System.out.println("耗时 " + (System.currentTimeMillis() - beginTime));
        }
    }
    
    class Job extends Thread {
        String jobName;
        long time = 0;
        CountDownLatch countDownLatch;
    
        public Job(String jobName, long time, CountDownLatch countDownLatch) {
            this.time = time;
            this.jobName = jobName;
            this.countDownLatch = countDownLatch;
        }
    
        @Override
        public void run() {
            System.out.println(jobName + "startDoSomeThing... " + new Date());
            doJob(time);
            System.out.println(jobName + "DoneJob " + new Date());
    
            //最好放在finally中
            countDownLatch.countDown();
        }
    
        private void doJob(long time) {
            try {
                Thread.sleep(time);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
    }
    
    
    /**
     * 执行结果:
     * job1startDoSomeThing... Thu Aug 24 09:17:01 CST 2017
     * job2startDoSomeThing... Thu Aug 24 09:17:01 CST 2017
     * job1DoneJob Thu Aug 24 09:17:04 CST 2017
     * job2DoneJob Thu Aug 24 09:17:06 CST 2017
     * do job3...
     * 耗时 5055
     */