[多线程] 等候任务线程结束

[多线程] 等待任务线程结束

使用多线程容易碰到这样的问题，主线程需要等待各个任务线程完成后再继续（如释放资源等）。

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常见的方法是在线程中使用计数器记录完成的线程数量，并且需要另外的一个线程轮询判断是否已经全部完成。

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方案一：

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final AtomicInteger counter = new AtomicInteger();public void testRun() {final int threadNum = 10;// 开启任务线程for (int i = 0; i < threadNum; i++) {new Thread(new WorkRunnable()).start();}// 开启一个监听线程等待所有工作线程运行完毕new Thread(new Runnable() {public void run() {while (true) {if (counter.get() == threadNum) {log.info("all threads finish");break;}else {try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}}}}}).start();}class WorkRunnable implements Runnable {public void run() {Random random = new Random();int interval = random.nextInt(10 * 1000);try {Thread.sleep(interval);} catch (InterruptedException e) {e.printStackTrace();}log.info(Thread.currentThread().getName() + " finish");counter.incrementAndGet();}}

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代码比较繁琐，监听线程等待100毫秒不会占用过多CPU资源。

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另外可以使用线程池来解决，运用JDK1.5的线程池新特性。

方案二：

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public void testRun() {int threadNum = 10;ExecutorService executor = Executors.newFixedThreadPool(threadNum);// 开启任务线程for (int i = 0; i < threadNum; i++) {executor.execute(new WorkRunnable());}// 阻塞直到全部完成后关闭while(!executor.isTerminated()) {executor.shutdown();}log.info("all threads finish");}class WorkRunnable implements Runnable {public void run() {Random random = new Random();int interval = random.nextInt(10 * 1000);try {Thread.sleep(interval);} catch (InterruptedException e) {e.printStackTrace();}log.info(Thread.currentThread().getName() + " finish");}}

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代码非常简洁，但是CPU占用很厉害?