一、CountDownLatch介绍;
* CountDownLatch是一种java.util.concurrent包下一个同步工具类;
* CountDownLatch能够使一个线程在等待另外一些线程完成各自工作之后,再继续执行。
* public void countDown() 锁存器的计数减1;
* public boolean await(long timeout,TimeUnit unit) 使当前线程在锁存器倒计数至零之前一直等待,除非线程被中断或超出了指定的等待时间。
二、应用场景介绍;
应用场景1:某一线程在开始运行前等待n个线程执行完毕;比如启动一个服务时,主线程需要等待多个组件加载完毕,之后再继续执行。
应用场景2:实现多个线程开始执行任务的最大并行性。注意是并行性,不是并发,强调的是多个线程在某一时刻同时开始执行。类似于赛跑,将多个线程放到起点,等待发令枪响,然后同时开跑。做法是初始化一个共享的CountDownLatch(1),将其计算器初始化为1,多个线程在开始执行任务前首先countdownlatch.await(),当主线程调用countDown()时,
计数器变为0,多个线程同时被唤醒。
三、样例代码;
1 public class CountDownLatchTest { 2 3 public static void main(String[] args) throws Exception{ 4 // TODO Auto-generated method stub 5 //场景1测试代码块开始 6 CountDownLatch latch = new CountDownLatch(2); 7 8 for(int i=0;i<2;i++){ 9 Thread thread = new Thread(new ComponentService(latch)); 10 thread.start(); 11 } 12 13 System.out.println("main thread begin..."); 14 latch.await(); //使当前线程在锁存器倒计数至零之前一直等待 15 System.out.println("main thread end...."); 16 //场景1测试代码块结束 17 System.out.println("===============长长的分割线================"); 18 //场景2测试代码块开始 19 CountDownLatch begin = new CountDownLatch(1); 20 for(int i=0;i<2;i++){ 21 Thread thread = new Thread(new Player(begin)); 22 thread.start(); 23 } 24 System.out.println("main thread begin..."); 25 begin.countDown(); 26 System.out.println("main thread end...."); 27 //场景2测试代码块结束 28 } 29 }
1 class ComponentService implements Runnable{ 2 private CountDownLatch latch; 3 public ComponentService(CountDownLatch latch) { 4 super(); 5 this.latch = latch; 6 } 7 8 @Override 9 public void run() { 10 // TODO Auto-generated method stub 11 System.out.println(Thread.currentThread().getName()+" 服务启动成功 !"); 12 latch.countDown(); 13 } 14 }
1 class Player implements Runnable{ 2 private CountDownLatch begin; 3 public Player(CountDownLatch begin) { 4 super(); 5 this.begin = begin; 6 } 7 8 @Override 9 public void run(){ 10 // TODO Auto-generated method stub 11 try { 12 begin.await(); 13 System.out.println(Thread.currentThread().getName()+" 起跑成功!"); 14 } catch (InterruptedException e) { 15 // TODO Auto-generated catch block 16 e.printStackTrace(); 17 } 18 } 19 }
执行结果:
四、部分内容转载说明;
部分来自网络整理:
https://www.cnblogs.com/Lee_xy_z/p/10470181.html
原文地址:https://www.cnblogs.com/crazytrip/p/11697595.html
时间: 2024-10-25 10:15:59