CountDownLatch

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

public class CountDownLatchTest {

	//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 
 public static void main(String[] args) throws InterruptedException {
	 ExecutorService newFixedThreadPool = Executors.newFixedThreadPool(10);
	 int num = 10;
	 CountDownLatch cdl = new CountDownLatch(num);
	 long start = System.currentTimeMillis();
	 for (int i = 0; i < num; i++) {
		 newFixedThreadPool.submit(new CountDownLatchRunnable(cdl));
	}
	 cdl.await();
    //TODO: 等待所有线程结束 做统计
	 long end = System.currentTimeMillis();
	 System.out.println((end-start)/1000);
	 newFixedThreadPool.shutdown();
 }
 
 public static class CountDownLatchRunnable implements Runnable{

	 private CountDownLatch cdl;
	 
	 public CountDownLatchRunnable(CountDownLatch cdl){
		 this.cdl = cdl; 
	 }
	 
	@Override
	public void run() {
		try {
			Thread.sleep(2000);
		} catch (InterruptedException e) { 
			e.printStackTrace();
		}
		cdl.countDown();
	}
	 
 }
 

}

//回环栅栏，通过它可以实现让一组线程等待至某个状态之后再全部同时执行。叫做回环是因为当所有等待线程都被释放以后，CyclicBarrier可以被重用。我们暂且把这个状态就叫做barrier，当调用await()方法之后，线程就处于barrier了。
 public static void main(String[] args) throws InterruptedException {
	 ExecutorService newFixedThreadPool = Executors.newFixedThreadPool(10);
	 int num = 10;
	 CountDownLatch cdl = new CountDownLatch(1); 
	 for (int i = 0; i < num; i++) {
		 newFixedThreadPool.submit(new CountDownLatchRunnable2(cdl));
	}
	 System.out.println("===========");
	 cdl.countDown(); 
	 
	 // 该实例时做压测是同时处理，起到高并发作用
	 newFixedThreadPool.shutdown();
 }
 
 public static class CountDownLatchRunnable2 implements Runnable{

	 private CountDownLatch cdl;
	 
	 public CountDownLatchRunnable2(CountDownLatch cdl){
		 this.cdl = cdl; 
	 }
	 
	@Override
	public void run() {
		
		try {
			cdl.await(); 
			 System.out.println("==================== ====="+System.currentTimeMillis());
		} catch (InterruptedException e) { 
			e.printStackTrace();
		}
		
	}
	 
 }
 

}

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