Java多線程之CountDownLatch

import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * CountDownLatch是個計數器，它有一個初始數， * 等待這個計數器的線程必須等到計數器倒數到零時才可繼續。 */public class CountDownLatchTest {/** * 初始化組件的線程 */public static class ComponentThread implements Runnable {// 計數器CountDownLatch latch;// 組件IDint ID;// 構造方法public ComponentThread(CountDownLatch latch, int ID) {this.latch = latch;this.ID = ID;}public void run() {// 初始化組件System.out.println("Initializing component " + ID);try {Thread.sleep(500 * ID);} catch (InterruptedException e) {}System.out.println("Component " + ID + " initialized!");//將計數器減一latch.countDown();}}/** * 啟動伺服器 */public static void startServer() throws Exception {System.out.println("Server is starting.");//初始化一個初始值為3的CountDownLatchCountDownLatch latch = new CountDownLatch(3);//起3個線程分別去啟動3個組件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個組件的初始化工作都完成latch.await();//當所需的三個組件都完成時，Server就可繼續了System.out.println("Server is up!");}public static void main(String[] args) throws Exception {CountDownLatchTest.startServer();}}