面试官：线程池如何按照core、max、queue的执行循序去执行？（内附详细解析）

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我们要明确线程代码的边界，异步化过程中，子线程抛出的异常应该由子线程自己去处理，而不是需要主线程感知来协助处理。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"解决方案"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"解决方案很简单，在虚拟机中，当一个线程如果没有显式处理异常而抛出时会将该异常事件报告给该线程对象的 "},{"type":"codeinline","content":[{"type":"text","text":"java.lang.Thread.UncaughtExceptionHandler"}]},{"type":"text","text":" 进行处理，如果线程没有设置 "},{"type":"codeinline","content":[{"type":"text","text":"UncaughtExceptionHandler"}]},{"type":"text","text":"，则默认会把异常栈信息输出到终端而使程序直接崩溃。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以如果我们想在线程意外崩溃时做一些处理就可以通过实现 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ThreadPoolExceptionTest {\n\n public static void main(String[] args) throws InterruptedException {\n MyHandler myHandler = new MyHandler();\n ExecutorService execute = new ThreadPoolExecutor(10, 10,\n 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue(), new ThreadFactoryBuilder().setUncaughtExceptionHandler(myHandler).build());\n\n TimeUnit.SECONDS.sleep(5);\n for (int i = 0; i < 10; i++) {\n execute.execute(new MyRunner());\n }\n }\n\n\n private static class MyRunner implements Runnable {\n @Override\n public void run() {\n int count = 0;\n while (true) {\n count++;\n System.out.println(\"我要开始生产Bug了============\");\n if (count == 10) {\n System.out.println(1 / 0);\n }\n\n if (count == 20) {\n System.out.println(\"这里是不会执行到的==========\");\n break;\n }\n }\n }\n }\n}\n\nclass MyHandler implements Thread.UncaughtExceptionHandler {\n private final static Logger LOGGER = LoggerFactory.getLogger(MyHandler.class);\n @Override\n public void uncaughtException(Thread t, Throwable e) {\n LOGGER.error(\"threadId = {}, threadName = {}, ex = {}\", t.getId(), t.getName(), e.getMessage());\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"执行结果："}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d2/d29eada0c31219a97c972ce03467f963.png","alt":"执行结果.png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"UncaughtExceptionHandler 解析"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们来看下"},{"type":"codeinline","content":[{"type":"text","text":"Thread"}]},{"type":"text","text":"中的内部接口"},{"type":"codeinline","content":[{"type":"text","text":"UncaughtExceptionHandler"}]},{"type":"text","text":"："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public class Thread {\n ......\n /**\n * 当一个线程因未捕获的异常而即将终止时虚拟机将使用 Thread.getUncaughtExceptionHandler()\n * 获取已经设置的 UncaughtExceptionHandler 实例，并通过调用其 uncaughtException(...) 方\n * 法而传递相关异常信息。\n * 如果一个线程没有明确设置其 UncaughtExceptionHandler，则将其 ThreadGroup 对象作为其\n * handler，如果 ThreadGroup 对象对异常没有什么特殊的要求，则 ThreadGroup 会将调用转发给\n * 默认的未捕获异常处理器（即 Thread 类中定义的静态未捕获异常处理器对象）。\n *\n * @see #setDefaultUncaughtExceptionHandler\n * @see #setUncaughtExceptionHandler\n * @see ThreadGroup#uncaughtException\n */\n @FunctionalInterface\n public interface UncaughtExceptionHandler {\n /**\n * 未捕获异常崩溃时回调此方法\n */\n void uncaughtException(Thread t, Throwable e);\n }\n\n /**\n * 静态方法，用于设置一个默认的全局异常处理器。\n */\n public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {\n defaultUncaughtExceptionHandler = eh;\n }\n\n /**\n * 针对某个 Thread 对象的方法，用于对特定的线程进行未捕获的异常处理。\n */\n public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {\n checkAccess();\n uncaughtExceptionHandler = eh;\n }\n\n /**\n * 当 Thread 崩溃时会调用该方法获取当前线程的 handler，获取不到就会调用 group（handler 类型）。\n * group 是 Thread 类的 ThreadGroup 类型属性，在 Thread 构造中实例化。\n */\n public UncaughtExceptionHandler getUncaughtExceptionHandler() {\n return uncaughtExceptionHandler != null ?\n uncaughtExceptionHandler : group;\n }\n\n /**\n * 线程全局默认 handler。\n */\n public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler() {\n return defaultUncaughtExceptionHandler;\n }\n ......\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"部分内容参考自：https://mp.weixin.qq.com/s/ghnNQnpou6-NemhFjpl4Jg"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"线程池发生了异常改怎样处理？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"线程池中线程运行过程中出现了异常该怎样处理呢？线程池提交任务有两种方式，分别是"},{"type":"codeinline","content":[{"type":"text","text":"execute()"}]},{"type":"text","text":"和"},{"type":"codeinline","content":[{"type":"text","text":"submit()"}]},{"type":"text","text":"，这里会依次说明。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"ThreadPoolExecutor.runWorker()实现"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"不管是使用"},{"type":"codeinline","content":[{"type":"text","text":"execute()"}]},{"type":"text","text":"还是"},{"type":"codeinline","content":[{"type":"text","text":"submit()"}]},{"type":"text","text":"提交任务，最终都会执行到"},{"type":"codeinline","content":[{"type":"text","text":"ThreadPoolExecutor.runWorker()"}]},{"type":"text","text":"，我们来看下源码（源码基于JDK1.8）："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/45/4533fca9daee72cebfcb29d680b46438.png","alt":"runWorker().png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们看到在执行"},{"type":"codeinline","content":[{"type":"text","text":"task.run()"}]},{"type":"text","text":"时，出现异常会直接向上抛出，这里处理的最好的方式就是在我们业务代码中使用"},{"type":"codeinline","content":[{"type":"text","text":"try...catch()"}]},{"type":"text","text":"来捕获异常。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"FutureTask.run()实现"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果我们使用"},{"type":"codeinline","content":[{"type":"text","text":"submit()"}]},{"type":"text","text":"来提交任务，在"},{"type":"codeinline","content":[{"type":"text","text":"ThreadPoolExecutor.runWorker()"}]},{"type":"text","text":"方法执行时最终会调用到"},{"type":"codeinline","content":[{"type":"text","text":"FutureTask.run()"}]},{"type":"text","text":"方法里面去，不清楚的小伙伴也可以看下我之前的文章："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"[线程池续：你必须要知道的线程池submit()实现原理之FutureTask！][2]"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c3/c3b06c75775d46854ba38c4569fe3943.png","alt":"FutureTask.run().png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这里可以看到，如果业务代码抛出异常后，会被"},{"type":"codeinline","content":[{"type":"text","text":"catch"}]},{"type":"text","text":"捕获到，然后调用"},{"type":"codeinline","content":[{"type":"text","text":"setExeception()"}]},{"type":"text","text":"方法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f9/f96ec090d886b19bd34f380cce97564f.png","alt":"FutureTask.setException().png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以看到其实类似于直接吞掉了，当我们调用"},{"type":"codeinline","content":[{"type":"text","text":"get()"}]},{"type":"text","text":"方法的时候异常信息会包装到FutureTask内部的变量outcome中，我们也会获取到对应的异常信息。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在"},{"type":"codeinline","content":[{"type":"text","text":"ThreadPoolExecutor.runWorker()"}]},{"type":"text","text":"最后"},{"type":"codeinline","content":[{"type":"text","text":"finally"}]},{"type":"text","text":"中有一个"},{"type":"codeinline","content":[{"type":"text","text":"afterExecute()"}]},{"type":"text","text":"钩子方法，如果我们重写了"},{"type":"codeinline","content":[{"type":"text","text":"afterExecute()"}]},{"type":"text","text":"方法，就可以获取到子线程抛出的具体异常信息"},{"type":"codeinline","content":[{"type":"text","text":"Throwable"}]},{"type":"text","text":"了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"结论"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对于线程池、包括线程的异常处理推荐以下方式:"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"直接使用"},{"type":"codeinline","content":[{"type":"text","text":"try/catch"}]},{"type":"text","text":"，这个也是最推荐的方式"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"在我们构造线程池的时候，重写"},{"type":"codeinline","content":[{"type":"text","text":"uncaughtException()"}]},{"type":"text","text":"方法，上面示例代码也有提到："}]}]}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public class ThreadPoolExceptionTest {\n\n public static void main(String[] args) throws InterruptedException {\n MyHandler myHandler = new MyHandler();\n ExecutorService execute = new ThreadPoolExecutor(10, 10,\n 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue(), new ThreadFactoryBuilder().setUncaughtExceptionHandler(myHandler).build());\n\n TimeUnit.SECONDS.sleep(5);\n for (int i = 0; i < 10; i++) {\n execute.execute(new MyRunner());\n }\n }\n}\n\nclass MyHandler implements Thread.UncaughtExceptionHandler {\n private final static Logger LOGGER = LoggerFactory.getLogger(MyHandler.class);\n @Override\n public void uncaughtException(Thread t, Throwable e) {\n LOGGER.error(\"threadId = {}, threadName = {}, ex = {}\", t.getId(), t.getName(), e.getMessage());\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3 直接重写"},{"type":"codeinline","content":[{"type":"text","text":"afterExecute()"}]},{"type":"text","text":"方法，感知异常细节"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"总结"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这篇文章到这里就结束了，不知道小伙伴们有没有一些感悟或收获？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过这几个面试问题，我也深刻的感受到学习知识要多思考，看源码的过程中要多设置一些场景，这样才会收获更多。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"[1]:https://xie.infoq.cn/article/6bd3b2d377832c5c2752f9a66"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"[2]:https://xie.infoq.cn/article/316d14bf0693470689f48ffa7"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ce/ce66cf44e1c5e8adae71e260b34e4139.png","alt":"原创干货分享.png","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}