如何捕捉panic

How to catch a panic

 

http://wiki.forum.nokia.com/index.php/How_to_catch_a_panic

 

http://wiki.forum.nokia.com/index.php/%E5%A6%82%E4%BD%95%E6%8D%95%E6%8D%89panic

 

 

From Forum Nokia Wiki

Yes, a panic. Although panics, by their nature, are uncatchable there is a way to prevent them from severely influencing your program.

First off, why would you do it? What is the use-case? Typically a panic draws attention to a programmatic error that should have already been corrected in the program. It always terminates the program execution and it's on purpose: programs panic from an unrecoverable stage. So why would we want to catch a panic if we were able to do so?

Well, there is at least one special use-case: in a test framework used for automated testing. In a typical unit testing framework, for example, where test suites containing test cases are being performed it's always a nice feature if the execution of tests doesn't get interrupted even in case of a fatal error. If the severe programming error doesn't harm other test cases, then it's ideal if the termination of a test case doesn't influence the life-time of other test cases.

Can panics be caught? At first sight, it may seem that User::SetExceptionHandler() would do. But it doesn't: exceptions are not the same as panics. So installing a new exception handler will not enable us to catch panics, even though it makes it possible to catch a small portion of ALL panics (e.g. an access violation aka KERN-EXE 3).

The ultimate solution is to let your test case run in a new thread. A new thread that you have control over: you create, destroy and most importantly monitor it. You can request notification when this thread dies normally or otherwise via RThread::Logon(). Combined this with RThread::ExitReason(), you can get a clue when and how a thread has exited. Even in case of a panic your main thread will not be affected at all so your - test - framework can continue to run.

The following example shows a console based exe which monitors other thread's death, displaying type and reason:

 

 

对，说的就是Panic。尽管就其本性来说，panic是“不可捕获的”，但仍有一种途径可以阻止它严重影响你的程序。

首先，为什么你要这样做呢？用况是什么？典型地，panic引起对应该已经在程序中更正的编程错误的注意。panic总是终止程序运行，并是故意这样设计的： 程序从“不可恢复的”运行阶段发生panic。因此，为什么我们需要捕获panic（假定我们能够这样做）？。

好了，至少有一个特殊的用处： 在测试框架中用于自动测试。在一个典型的单元测试框架中，比如，执行含有测试用例的测试集，若即使发生致命错误测试也不中断，这总是一个很好的功能。如果严重的编程错误不伤害其它的测试用例，那么某个测试用例的终止不影响其它用例的生命周期将是很理想的。

panic能被捕获吗？乍看起来，似乎User::SetExceptionHandler()能办到。但它却办不到。异常与panic不同。因此，安装一个新异常处理器不会使我们能捕获到panic,即使它使捕获一小部分异常成为可能（比如，访问违规或者说KERN-EXE 3）。

最终的解决方案: 让你的测试用例'运行在一个新线程中。一个你控制的新线程： 创建、销毁它，最重要的是监视它。经由RThread::Logon()你能够请求获知线程死亡正常与否。

下例演示了基于一个控制台的Exe，检测其他线程的死亡，显示类型及原因：

 

 

 #ifndef THREADNOTIFIER_H #define THREADNOTIFIER_H #include <e32base.h> class CThreadNotifier : public CActive { public: CThreadNotifier(); ~CThreadNotifier(); void ConstructL(); void IssueRequest(); protected: void RunL(); void DoCancel(); TInt RunError(TInt aError); RUndertaker iUndertaker; TInt iThreadHandle; }; #endif

 

#include "ThreadNotifier.h" #include <e32cons.h> _LIT(KPanicMsg, "THREAD-NOTIFIER"); LOCAL_D CConsoleBase* console; CThreadNotifier::CThreadNotifier() : CActive(CActive::EPriorityStandard) { CActiveScheduler::Add(this); } void CThreadNotifier::ConstructL() { User::LeaveIfError(iUndertaker.Create()); } CThreadNotifier::~CThreadNotifier() { Cancel(); iUndertaker.Close(); } void CThreadNotifier::IssueRequest() { __ASSERT_ALWAYS(!IsActive(), User::Panic(KPanicMsg, 0)); iUndertaker.Logon(iStatus, iThreadHandle); SetActive(); } void CThreadNotifier::RunL() { if (iStatus == KErrDied) { RThread thread; thread.SetHandle(iThreadHandle); console->Printf(_L("Thread %S (%d) died (Type: %d, reason %d)/n"), &thread.Name(), (int)thread.Id(), thread.ExitType(), thread.ExitReason()); thread.Close(); } IssueRequest(); } void CThreadNotifier::DoCancel() { iUndertaker.LogonCancel(); } TInt CThreadNotifier::RunError(TInt /*aError*/) { return KErrNone; } LOCAL_C void callExampleL() { console = Console::NewL(_L("Thread Notifier"), TSize(KDefaultConsWidth, KDefaultConsHeight)); CleanupStack::PushL(console); CActiveScheduler* scheduler = new(ELeave) CActiveScheduler; CleanupStack::PushL(scheduler); CActiveScheduler::Install(scheduler); CThreadNotifier* notifier = new(ELeave) CThreadNotifier; CleanupStack::PushL(notifier); notifier->ConstructL(); notifier->IssueRequest(); CActiveScheduler::Start(); CleanupStack::PopAndDestroy(3, console); // console, scheduler, notifier } GLDEF_C TInt E32Main() { __UHEAP_MARK; CTrapCleanup* cleanup = CTrapCleanup::New(); TRAPD(error, callExampleL()); __ASSERT_ALWAYS(!error, User::Panic(KPanicMsg, error)); delete cleanup; __UHEAP_MARKEND; return 0; }