经营你的iOS应用日志（二）：异常日志

开发iOS应用，解决Crash问题始终是一个难题。Crash分为两种，一种是由EXC_BAD_ACCESS引起的，原因是访问了不属于本进程的内存地址，有可能是访问已被释放的内存；另一种是未被捕获的Objective-C异常（N***ception），导致程序向自身发送了SIGABRT信号而崩溃。其实对于未捕获的Objective-C异常，我们是有办法将它记录下来的，如果日志记录得当，能够解决绝大部分崩溃的问题。这里对于UI线程与后台线程分别说明。

先看UI线程。iOS SDK提供了NSSetUncaughtExceptionHandler函数，用法如：

NSSetUncaughtExceptionHandler( handleRootException );

这样在UI线程发生未捕获异常后，进程崩溃之前，handleRootException会被执行。这个函数实现如下

static void handleRootException( N***ception* exception )
{
NSString* name = [ exception name ];
NSString* reason = [ exception reason ];
NSArray* symbols = [ exception callStackSymbols ]; // 异常发生时的调用栈
NSMutableString* strSymbols = [ [ NSMutableString alloc ] init ]; // 将调用栈拼成输出日志的字符串
for ( NSString* item in symbols )
{
[ strSymbols appendString: item ];
[ strSymbols appendString: @"\r\n" ];
}

// 写日志，级别为ERROR
writeCinLog( __FUNCTION__, CinLogLevelError, @"[ Uncaught Exception ]\r\nName: %@, Reason: %@\r\n[ Fe Symbols Start ]\r\n%@[ Fe Symbols End ]", name, reason, strSymbols );
[ strSymbols release ];

// 这儿必须Hold住当前线程，等待日志线程将日志成功输出，当前线程再继续运行
blockingFlushLogs( __FUNCTION__ );

// 写一个文件，记录此时此刻发生了异常。这个挺有用的哦
NSDictionary* dict = [ NSDictionary dictionaryWithObjectsAndKeys:
currentCinLogFileName(), @"LogFile", // 当前日志文件名称
currentCinLogFileFullPath(), @"LogFileFullPath", // 当前日志文件全路径
[ NSDate date ], @"TimeStamp", // 异常发生的时刻
nil ];
NSString* path = [ NSString stringWithFormat: @"%@/Documents/", NSHomeDirectory() ];
NSString* lastExceptionLog = [ NSString stringWithFormat: @"[e-mail]", path ];
[ dict writeToFile: lastExceptionLog atomically: YES ];

}

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而我们的日志组件必须实现blockingFlushLogs函数，确保进程在日志完全写入文件后再退出。这个实现应该很简单吧。

当应用下次启动时，我们可以检查，如果有LastExceptionLog.txt，则弹窗引导测试人员将日志发过来。如果iPhone上面配置了EMail帐户，可以很简单的调用MFMailComposeViewController将日志文件作为附件发送，当然也可以想其它办法。

记得正式发布的版本要将它条件编译去掉哦。

其中文件中的最后一条ERROR即为导致崩溃的异常，而从ERROR之前的日志可以看出当前程序的运行情况。ERROR如下：

<- 03-20 17:21:43 ERROR -> [UI] -[CinUIRunLoopActionManager(Protected) handleRootException:]
[ Uncaught Exception ]
Name: NSDestinationInvalidException, Reason: *** -[CinThreadRunLoopActionManager performSelector:onThread:withObject:waitUntilDone:modes:]: target thread exited while waiting for the perform
[ Fe Symbols Start ]
0 CoreFoundation 0x340c88d7 __exceptionPreprocess + 186
1 libobjc.A.dylib 0x343181e5 objc_exception_throw + 32
2 CoreFoundation 0x340c87b9 +[N***ception raise:format:] + 0
3 CoreFoundation 0x340c87db +[N***ception raise:format:] + 34
4 Foundation 0x35a12493 -[NSObject(NSThreadPerformAdditions) performSelector:onThread:withObject:waitUntilDone:modes:] + 998
5 Foundation 0x35a3afb5 -[NSObject(NSThreadPerformAdditions) performSelector:onThread:withObject:waitUntilDone:] + 108
6 MyiOSapplication 0x0022b7e9 -[CinThreadRunLoopActionManager(Protected) performAction:] + 144
13 UIKit 0x374b36b5 -[UIViewController _setViewAppearState:isAnimating:] + 144
14 UIKit 0x374b38c1 -[UINavigationController viewWillAppear:] + 288
15 UIKit 0x374b36b5 -[UIViewController _setViewAppearState:isAnimating:] + 144
16 UIKit 0x3750e61b -[UIViewController beginAppearanceTransition:animated:] + 190
17 UIKit 0x3750b415 -[UITabBarController transitionFromViewController:toViewController:transition:shouldSetSelected:] + 184
18 UIKit 0x3750b357 -[UITabBarController transitionFromViewController:toViewController:] + 30
19 UIKit 0x3750ac91 -[UITabBarController _setSelectedViewController:] + 300
20 UIKit 0x3750a9c5 -[UITabBarController setSelectedIndex:] + 240
21 MyiOSapplication 0x0007ef1d +[Utility ResetCurrentTabIndex] + 172
22 MyiOSapplication 0x001a87bd -[UIViewController(statusBar) dismissModalViewControllerAnimatedEx:] + 416
23 MyiOSapplication 0x001793fb -[ImageProcessingViewController save:] + 690
24 CoreFoundation 0x34022435 -[NSObject performSelector:withObject:withObject:] + 52
25 UIKit 0x3748c9eb -[UIApplication sendAction:to:from:forEvent:] + 62
26 UIKit 0x3748c9a7 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 30
27 UIKit 0x3748c985 -[UIControl sendAction:to:forEvent:] + 44
28 UIKit 0x3748c6f5 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 492
29 UIKit 0x3748d02d -[UIControl touchesEnded:withEvent:] + 476
30 UIKit 0x3748b50f -[UIWindow _sendTouchesForEvent:] + 318
31 UIKit 0x3748af01 -[UIWindow sendEvent:] + 380
32 UIKit 0x374714ed -[UIApplication sendEvent:] + 356
33 UIKit 0x37470d2d _UIApplicationHandleEvent + 5808
34 GraphicsServices 0x308a3df3 PurpleEventCallback + 882
35 CoreFoundation 0x3409c553 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 38
36 CoreFoundation 0x3409c4f5 __CFRunLoopDoSource1 + 140
37 CoreFoundation 0x3409b343 __CFRunLoopRun + 1370
38 CoreFoundation 0x3401e4dd CFRunLoopRunSpecific + 300
39 CoreFoundation 0x3401e3a5 CFRunLoopRunInMode + 104
40 GraphicsServices 0x308a2fcd GSEventRunModal + 156
41 UIKit 0x3749f743 UIApplicationMain + 1090
42 MyiOSapplication 0x000d4ccb main + 174
43 MyiOSapplication 0x000039c8 start + 40
[ Fe Symbols End ]

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可以看到，即使我们没有编译时生成的符号文件，也能够打印出调用栈上的每个函数的名称，只是没有文件名和行号。

那么，除了UI线程之外，自己创建的后台线程呢？运行NSRunLoop的后台线程的线程函数应该如下：

- ( void ) threadProc: ( NSString* )threadName
{
NSThread* current = [ NSThread currentThread ];
[ current setName: threadName ];
NSAutoreleasePool *pool = [ [ NSAutoreleasePool alloc ] init ];

// 一个没有实际作用的NSTimer，确保NSRunLoop不退出。不知道有没有更好的办法啊
_dummyTimer = [ [ NSTimer timerWithTimeInterval: 10.0
target: self
selector: @selector( dummyTimerProc: )
userInfo: nil
repeats: YES ] retain ];

NSRunLoop *r = [ NSRunLoop currentRunLoop ];
[ r addTimer: _dummyTimer forMode: NSDefaultRunLoopMode ];
@try {
// 启动后台线程的NSRunLoop
[ r run ];
}
@catch ( N***ception *exception ) {
[ self handleRootException: exception ];
// 一旦在线程根上捕捉到未知异常，记录异常后本线程退出
}
@finally {
[ _dummyTimer invalidate ];
[ _dummyTimer release ];
[ pool release ];
}
}

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后台线程的handleRootException与UI线程基本一致。不过为了测试人员更加方便，其实只要不是UI线程发生未捕获异常，都可以先引导用户发送日志，再把进程崩溃掉。