为了防止一个应用占用过多的系统资源，苹果设计了一个“看门狗”(watchdog)的机制。在不同的场景下，“看门狗”会监测应用的性能。 如果超出了该场景所规定的运行时间，“看门狗”就会强制终结这个应用的进程。 开发者们在crashlog里面，会看到诸如0x8badf00d这样的错误代码。 异常代码：“0x8badf00d”，即“ate bad food”。

如果我们的应用程序对一些特定的UI事件（比如启动、挂起、恢复、结束）响应不及时，Watchdog会把我们的应用程序干掉，并生成一份响应的crash报告。

苹果开发文档原文：

• The exception code 0x8badf00d indicates that an application has been terminated by iOS because a watchdog timeout occurred. The application took too long to launch, terminate, or respond to system events. One common cause of this is doing. Whatever operation is on Thread 0 needs to be moved to a background thread, or processed differently, so that it does not block the main thread.