多线程学习--------CountDownLatch

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1.概述

犹如倒计时计数器，调用CountDownLatch对象的countDown方法就将计数器减1，当计数到达0时，则所有等待者开始执行。

2.代码示例

public static void main(String[] args) {
		
		ExecutorService executorService = Executors.newCachedThreadPool();
		CountDownLatch orderLatch = new CountDownLatch(1);
		CountDownLatch answerLatch = new CountDownLatch(3);
		for(int i = 0;i < 3;i++){
			Runnable runnable = new Runnable() {
				@Override
				public void run() {
					try {
						System.out.println("线程"+Thread.currentThread().getName()+"正在等待接收命令");
						//等待命令
						orderLatch.await();
						//接收命令(orderLatch的数量减到0)
						System.out.println("线程"+Thread.currentThread().getName()+"已经接收命令");
						//执行
						Thread.sleep((long)Math.random()*10000);
						//执行完毕
						System.out.println("线程"+Thread.currentThread().getName()+"回应处理结果");
						//执行完某个线程，使得answerCountDownLatch减1
						answerLatch.countDown();
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
					
				}
			};
			executorService.execute(runnable);
		}
		try {
			Thread.sleep((long)Math.random()*10000);
			System.out.println("线程"+Thread.currentThread().getName()+"即将发布命令");
			//发布命令
			orderLatch.countDown();
			System.out.println("线程"+Thread.currentThread().getName()+"已经发布命令,正在等待结果");
			//等待所有的answer执行完
			answerLatch.await();
			//所有answer执行完毕，裁判拿到所有人的结果
			System.out.println("线程"+Thread.currentThread().getName()+"已经获取到所有结果");
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		executorService.shutdown();
		
		
	}

运行结果: