Java多线程之CountDownLatch

转 http://blog.youkuaiyun.com/huang_xw/article/details/7090146

    import java.util.concurrent.CountDownLatch;  
    import java.util.concurrent.ExecutorService;  
    import java.util.concurrent.Executors;  
      
    /** 
     * CountDownLatch是个计数器，它有一个初始数， 
     * 等待这个计数器的线程必须等到计数器倒数到零时才可继续。 
     */  
    public class CountDownLatchTest {  
      
        /** 
         * 初始化组件的线程 
         */  
        public static class ComponentThread implements Runnable {  
            // 计数器  
            CountDownLatch latch;  
            // 组件ID  
            int ID;  
      
            // 构造方法  
            public ComponentThread(CountDownLatch latch, int ID) {  
                this.latch = latch;  
                this.ID = ID;  
            }  
      
            public void run() {  
                // 初始化组件  
                System.out.println("Initializing component " + ID);  
                try {  
                    Thread.sleep(500 * ID);  
                } catch (InterruptedException e) {  
                }  
                System.out.println("Component " + ID + " initialized!");  
                //将计数器减一  
                latch.countDown();  
            }  
        }  
      
        /** 
         * 启动服务器 
         */  
        public static void startServer() throws Exception {  
            System.out.println("Server is starting.");  
            //初始化一个初始值为3的CountDownLatch  
            CountDownLatch latch = new CountDownLatch(3);  
            //起3个线程分别去启动3个组件  
            ExecutorService service = Executors.newCachedThreadPool();  
            service.submit(new ComponentThread(latch, 1));  
            service.submit(new ComponentThread(latch, 2));  
            service.submit(new ComponentThread(latch, 3));  
            service.shutdown();  
      
            //等待3个组件的初始化工作都完成  
            latch.await();  
      
            //当所需的三个组件都完成时，Server就可继续了  
            System.out.println("Server is up!");  
        }  
      
        public static void main(String[] args) throws Exception {  
            CountDownLatchTest.startServer();  
        }  
    }