并发工具类：倒计时器-CountDownLatch

---

title: 并发工具类：倒计时器-CountDownLatch author: Enjoyitlife.top date: 2019-10-01 10:51:33 summary: JUC包中的工具类CountDownLatch到底给我们提供了什么功能？ categories: Concurrent tags:

• Concurrent-Tools

---

并发工具类：倒计时器-CountDownLatch

CountDownLatch是JDK1.5提供一个并发编程辅助类，用于控制一个和多个线程进行等待，直到其他线程完成后在执行任务。

常用方法：

• CountDownLatch latch= new CountDownLatch(10); 构造方法，设定计数值，即要等待的线程数量。
• void countDown() 计数器的值减1，直到为0
• void await() 阻塞等待，直到计数器的值为0
• long getCount() 获取当前计数器的值

应用场景 1：实现多个N个线程并行运行

平常用于在创建N个线程来，验证接口的性能。

public class CountDownLatchTest {
	public static void main(String[] args) {
		CountDownLatch latch= new CountDownLatch(5);
		try {	
			for(int i=0;i<5;i++) {
				new Thread(new Runnable() {
					@Override
					public void run() {
						CountDownLatchTest.sayThreadName();
					}
				}).start();
			}		
			latch.await();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}	
	}
	/***
	*模拟真正接口
	*/
	public static void sayThreadName() {
		System.out.println(System.currentTimeMillis()+"^^"+Thread.currentThread().getName()+"^^^^");
	}	
}

应用场景2：等待N个线程完成任务后在触发其他操作

运动员准备完毕后裁判发令，裁判发令后运动员开始跑步。

public class AthleticMeeting {
	
	public static void main(String[] args) throws InterruptedException {
		//准备队列
		CountDownLatch readLatch = new CountDownLatch(8);
		//结束队列
		CountDownLatch endLatch = new CountDownLatch(8);
		//教练队列
		CountDownLatch  refereeLatch=new CountDownLatch(1);	
		for(int i=0;i<8;i++) {
			final int payerId=i+1;
			Thread thread= new Thread(new Runnable() {
				@Override
				public void run() {
					try {
						Long readyCosts=new Double(Math.random()*5000).longValue();
						Thread.sleep(readyCosts);
						System.out.println(payerId+"号运动员耗时"+readyCosts+"毫秒准备完毕！");
						readLatch.countDown();					
						refereeLatch.await();					
						Long runCost=new Double(Math.random()*5000).longValue();
						Thread.sleep(runCost);
						System.out.println(payerId+"号运动员耗时"+runCost+"毫秒完成比赛！");
						endLatch.countDown();					
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			});
			thread.start();
		}
		readLatch.await();
		System.out.println("所有运动员准备完毕！");
		refereeLatch.countDown();
		System.out.println("裁判发动发令枪！");
		endLatch.await();
		System.out.println("比赛完成！");	
	}		
}