关于异常捕获那些事

iOS提供的异常捕获功能比较简单，它能捕获到一些数据越界，发送方法的错误，但是捕获不到内存级别的错误，网上搜了一个类，捕获这个内存级别的问题，包括友盟都是这么干得，

一篇老外的文章也是介绍异常捕获的情况：http://www.mikeash.com/pyblog/friday-qa-2011-04-01-signal-handling.html

还有C和指针上也有一段关于异常的介绍:Page:338 关于信号的介绍

根据它的说法，当一些异常的信号发生的时候，程序会做出缺省的反应，没有什么标准的缺省的反应，但大部分的编译器都选择了终止应用程序，也就是我们说的程序crash了。我们可以去设置一些信号处理函数，当异常信号发生的时候，我们指定它们帮我们处理一些事情。

据C和指针描述信号处理函数能做的事情非常少: 除了能向一个静态变量赋值外，无法访问其他任何静态数据。

.h文件

#import <Foundation/Foundation.h>

@interface UncaughtExceptionHandler : NSObject
{
BOOL dismissed;
}

void InstallUncaughtExceptionHandler();

@end

.m文件

#import "UncaughtExceptionHandler.h"

#include <libkern/OSAtomic.h>

#include <execinfo.h>

NSString *const UncaughtExceptionHandlerSignalExceptionName =@"UncaughtExceptionHandlerSignalExceptionName";

NSString *const UncaughtExceptionHandlerSignalKey =
@"UncaughtExceptionHandlerSignalKey";

NSString *const UncaughtExceptionHandlerAddressesKey =
@"UncaughtExceptionHandlerAddressesKey";

volatile int32_t UncaughtExceptionCount = 0;
const int32_t UncaughtExceptionMaximum = 10;
const NSInteger UncaughtExceptionHandlerSkipAddressCount = 0;
const NSInteger UncaughtExceptionHandlerReportAddressCount = 10;
@implementation UncaughtExceptionHandler
void InstallUncaughtExceptionHandler()
{
signal(SIGABRT, MySignalHandler);
signal(SIGILL, MySignalHandler);
signal(SIGSEGV, MySignalHandler);
signal(SIGFPE, MySignalHandler);
signal(SIGBUS, MySignalHandler);
signal(SIGPIPE, MySignalHandler);
}

+ (NSArray *)backtrace
{
void* callstack[128];
int frames = backtrace(callstack, 128);
char **strs = backtrace_symbols(callstack, frames);
int i;
NSMutableArray *backtrace = [NSMutableArray arrayWithCapacity:frames];
for (
i = UncaughtExceptionHandlerSkipAddressCount;
i < UncaughtExceptionHandlerSkipAddressCount +
UncaughtExceptionHandlerReportAddressCount;
i++)
{
[backtrace addObject:[NSString stringWithUTF8String:strs[i]]];
}
free(strs);
return backtrace;
}

- (void)alertView:(UIAlertView *)anAlertView clickedButtonAtIndex:(NSInteger)anIndex

{
if (anIndex == 0)
{
dismissed =YES;
}
}
- (void)handleException:(NSException *)exception

{
NSLog(@"%@",[[exception userInfo] objectForKey:UncaughtExceptionHandlerAddressesKey]);
UIAlertView *alert =
[[[UIAlertView alloc]

initWithTitle:NSLocalizedString(@"Unhandled exception",nil)

message:[NSString stringWithFormat:NSLocalizedString(

@"You can try to continue but the application may be unstable.\n"
@"%@\n%@",
nil),
[exception reason],
[[exception userInfo] objectForKey:UncaughtExceptionHandlerAddressesKey]]
delegate:self
cancelButtonTitle:NSLocalizedString(@"Quit",nil)
otherButtonTitles:NSLocalizedString(@"Continue",nil),
nil]
autorelease];
[alert show];
CFRunLoopRef runLoop = CFRunLoopGetCurrent();
CFArrayRef allModes = CFRunLoopCopyAllModes(runLoop);
while (!dismissed)
{
for (NSString *modein (NSArray *)allModes)
{
CFRunLoopRunInMode((CFStringRef)mode, 0.001,false);
}
}
CFRelease(allModes);
NSSetUncaughtExceptionHandler(NULL);
signal(SIGABRT, SIG_DFL);
signal(SIGILL, SIG_DFL);
signal(SIGSEGV, SIG_DFL);
signal(SIGFPE, SIG_DFL);
signal(SIGBUS, SIG_DFL);
signal(SIGPIPE, SIG_DFL);
if ([[exception name] isEqual:UncaughtExceptionHandlerSignalExceptionName])
{
kill(getpid(), [[[exception userInfo] objectForKey:UncaughtExceptionHandlerSignalKey] intValue]);
}

else
{
[exception raise];
}
}
void MySignalHandler(int signal)
{
int32_t exceptionCount = OSAtomicIncrement32(&UncaughtExceptionCount);
if (exceptionCount > UncaughtExceptionMaximum)
{

return;
}
NSMutableDictionary *userInfo =
[NSMutableDictionary dictionaryWithObject:[NSNumber numberWithInt:signal] forKey:UncaughtExceptionHandlerSignalKey];
NSArray *callStack = [UncaughtExceptionHandler backtrace];
[userInfo setObject:callStack forKey:UncaughtExceptionHandlerAddressesKey];
[[[[UncaughtExceptionHandler alloc] init] autorelease]
performSelectorOnMainThread:@selector(handleException:)
withObject: [NSException exceptionWithName:UncaughtExceptionHandlerSignalExceptionName
reason: [NSString stringWithFormat:NSLocalizedString(@"Signal %d was raised.\n"@"%@%@",nil),signal,
getAppInfo(),callStack]

userInfo:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:signal]
forKey:UncaughtExceptionHandlerSignalKey]]waitUntilDone:YES];
}
NSString* getAppInfo()
{
NSString *appInfo = [NSString stringWithFormat:@"App :%@ %@ %@(%@)\nDevice : %@\nOS Version : %@ %@\nUDID :\n",
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleDisplayName"],
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleShortVersionString"],
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"],
[UIDevice currentDevice].model,
[UIDevice currentDevice].systemName,
[UIDevice currentDevice].systemVersion,
[UIDevice currentDevice].uniqueIdentifier];
NSLog(@"Crash!!!! %@", appInfo);

return appInfo;

}

@end

可以看到是利用了unix底层的一些性能去做了一些处理.