<pre code_snippet_id="569358" snippet_file_name="blog_20150417_1_1404918" name="code" class="java">CountDownLatch是一个同步工具类,它允许一个或多个线程一直等待,直到其他线程的操作执行完后再执行
</pre><pre code_snippet_id="569358" snippet_file_name="blog_20150417_3_2248647" name="code" class="java">
package com.sgcc.uds.search.mq; import java.util.concurrent.CountDownLatch; /** * CountDownlatch,是一种Sychronizer,它可以延迟线程的进度直到线程的进度到线程到达终止状态。 它本身而言是Java并发包中非常有用的一个类,它可以让某些任务完成以后再继续运行下面的内容, 每个任务本身执行完毕后让计数器减一,直到计数器清零后,以下的内容才可以继续运行,否则将阻塞等待。 想了一下,这个场景非常适合用于项目中这样的场景: 我们有个项目,它需要三个第三方的API, 并把结果拿到,在一个线程中顺序去拿结果没有问题,但是这里这三个任务是非常耗时的操作, 如果顺序获取性能非常差,因此可以考虑用三个线程,当三个线程拿到结果后才继续主线程的工作, 等三个线程运行结束后,由主线程去取子线程运行的结果。 这里有个很重要的前提:我们的系统运行在4个cpu的server上, 这样多线程才能体现性能,JVM会分配这些线程尽量运行在不同的cpu上。 * @author Administrator * */ public class CountDownLatchSample { public static void main(String[] args) { String[] strs = getResult(); for (int i = 0; i < strs.length; i++) { System.out.println(strs[i]); } } public static String[] getResult(){ String[] strs = new String[3]; CountDownLatch countDownLatch = new CountDownLatch(3); Work1 work1 = new Work1(countDownLatch,strs[0]); Work2 work2 = new Work2(countDownLatch,strs[1]); Work3 work3 = new Work3(countDownLatch,strs[2]); work1.start(); work2.start(); work3.start(); try { countDownLatch.await(); } catch (InterruptedException e) { e.printStackTrace(); } strs[0] = work1.str1; strs[1] = work2.str2; strs[2] = work3.str3; return strs; } } class Work1 extends Thread{ public String str1; public CountDownLatch latch1; public Work1(CountDownLatch latch1,String str1){ this.latch1 = latch1; this.str1 = str1; } public void run(){ str1="work1"; latch1.countDown(); } } class Work2 extends Thread{ public String str2; public CountDownLatch latch2; public Work2(CountDownLatch latch2,String str2){ this.latch2 = latch2; this.str2 = str2; } public void run(){ try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } str2="work2"; latch2.countDown(); } } class Work3 extends Thread{ public String str3; public CountDownLatch latch3; public Work3(CountDownLatch latch3,String str3){ this.latch3 = latch3; this.str3 = str3; } public void run(){ try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } str3="work3"; latch3.countDown(); } }
package com.sgcc.uds.search.mq; import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.CountDownLatch; public class CountDownLatchWorkerDemo { final static SimpleDateFormat sdf = new SimpleDateFormat( "yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { CountDownLatch latch = new CountDownLatch(2);// 两个工人的协作 Worker worker1 = new Worker("zhang san", 5000, latch); Worker worker2 = new Worker("li si", 5000, latch); worker1.start();// worker2.start();// latch.await();// 等待所有工人完成工作 System.out.println("all work done at " + sdf.format(new Date())); } static class Worker extends Thread { String workerName; int workTime; CountDownLatch latch; public Worker(String workerName, int workTime, CountDownLatch latch) { this.workerName = workerName; this.workTime = workTime; this.latch = latch; } public void run() { System.out.println("Worker " + workerName + " do work begin at " + sdf.format(new Date())); doWork();// 工作了 System.out.println("Worker " + workerName + " do work complete at " + sdf.format(new Date())); latch.countDown();// 工人完成工作,计数器减一 } private void doWork() { try { Thread.sleep(workTime); } catch (InterruptedException e) { e.printStackTrace(); } } } }
package com.sgcc.uds.search.mq; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * * @author Administrator *该程序用来模拟发送命令与执行命令,主线程代表指挥官,新建3个线程代表战士,战士一直等待着指挥官下达命令, *若指挥官没有下达命令,则战士们都必须等待。一旦命令下达,战士们都去执行自己的任务,指挥官处于等待状态, *战士们任务执行完毕则报告给指挥官,指挥官则结束等待。 */ public class CountdownLatchOrderTest { public static void main(String[] args) { ExecutorService service = Executors.newCachedThreadPool(); //创建一个线程池 final CountDownLatch cdOrder = new CountDownLatch(1);//指挥官的命令,设置为1,指挥官一下达命令,则cutDown,变为0,战士们执行任务 final CountDownLatch cdAnswer = new CountDownLatch(3);//因为有三个战士,所以初始值为3,每一个战士执行任务完毕则cutDown一次,当三个都执行完毕,变为0,则指挥官停止等待。 for(int i=0;i<3;i++){ Runnable runnable = new Runnable(){ public void run(){ try { System.out.println("线程" + Thread.currentThread().getName() + "正准备接受命令"); cdOrder.await(); //战士们都处于等待命令状态 System.out.println("线程" + Thread.currentThread().getName() + "已接受命令"); Thread.sleep((long)(Math.random()*10000)); System.out.println("线程" + Thread.currentThread().getName() + "回应命令处理结果"); cdAnswer.countDown(); //任务执行完毕,返回给指挥官,cdAnswer减1。 } catch (Exception e) { e.printStackTrace(); } } }; service.execute(runnable);//为线程池添加任务 } try { Thread.sleep((long)(Math.random()*10000)); System.out.println("线程" + Thread.currentThread().getName() + "即将发布命令"); cdOrder.countDown(); //发送命令,cdOrder减1,处于等待的战士们停止等待转去执行任务。 System.out.println("线程" + Thread.currentThread().getName() + "已发送命令,正在等待结果"); cdAnswer.await(); //命令发送后指挥官处于等待状态,一旦cdAnswer为0时停止等待继续往下执行 System.out.println("线程" + Thread.currentThread().getName() + "已收到所有响应结果"); } catch (Exception e) { e.printStackTrace(); } service.shutdown(); //任务结束,停止线程池的所有线程 } }
package com.sgcc.uds.search.mq; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; // 一个CountDouwnLatch实例是不能重复使用的,也就是说它是一次性的, //锁一经被打开就不能再关闭使用了,如果想重复使用,请考虑使用CyclicBarrier。 public class CountDownLatch100Test { // 模拟了100米赛跑,10名选手已经准备就绪,只等裁判一声令下。当所有人都到达终点时,比赛结束。 public static void main(String[] args) throws InterruptedException { // 开始的倒数锁 final CountDownLatch begin = new CountDownLatch(1); // 结束的倒数锁 final CountDownLatch end = new CountDownLatch(10); // 十名选手 final ExecutorService exec = Executors.newFixedThreadPool(10); for (int index = 0; index < 10; index++) { final int NO = index + 1; Runnable run = new Runnable() { public void run() { try { // 如果当前计数为零,则此方法立即返回。 // 等待 begin.await(); Thread.sleep((long) (Math.random() * 10000)); System.out.println("No." + NO + " arrived"); } catch (InterruptedException e) { } finally { // 每个选手到达终点时,end就减一 end.countDown(); } } }; exec.submit(run); } System.out.println("Game Start"); // begin减一,开始游戏 begin.countDown(); // 等待end变为0,即所有选手到达终点 end.await(); System.out.println("Game Over"); exec.shutdown(); } }