NET环境下的未处理异常(unhandled exception)的解决方案
NET环境下的未处理异常(unhandled exception )的解决方案
.Net 框架提供了非常强大的异常处理机制,同时对一些非托管代码很难控制的系统问题比如指针越界,内存泄漏等提供了很好的解决方案。相比非托管代码构建的系 统,.Net构建的系统更加稳定。不过这并不是说.Net构建的系统就完全无懈可击,很多由于代码的不严谨或者系统问题引发的故障将会导致.Net应用程 序产生未捕获异常,从而导致应用程序异常终止。
本文将对三种最常见的.Net应用的未捕获异常处理进行阐述。
在开始本文之前,让我们来看看.Net在什么情况下会产生未捕获异常。未捕获异常从定义上说就是结构化异常处理未能捕获的异常。通俗的讲就是发生在Try Catch块意外的异常。那么是不是我们在Main函数中加一个Try Catch 块就可以捕获全部未捕获异常了呢?答案是否定的。这里面有两种情况无法通过这种方法捕获:
1. GC 产生的异常,这种异常通常因为Finalize函数中引发未捕获异常引起。当然这并不绝对,一些系统问题比如内存耗尽有时候也会造成GC异常。
2. 主线程以为的线程引发的未捕获异常。这些异常我们往往可以在线程的主函数中用Try Catch 来捕获,但如果系统中使用了外部的组件,或者甚至是.Net 框架自带的一些系统组件,由这些组件的线程引发的异常,调用代码无法通过Try Catch来捕获。
从上面两点来看,即使我们的代码在每个地方都加了Try Catch ,也不能百分百杜绝未捕获异常的发生。
鉴于此,为了提高系统的健壮性和可维护性,我们需要通过一种方法来截获这些未捕获异常,并进行适当的处理。
.Net 的设计者已经考虑到这些问题,并且为我们提供了一个叫 UnhandledExceptionEventHandler 的事件,通过这个事件,我们可以截获未捕获异常,并进行处理。
这个事件的事件参数UnhandledExceptionEventArgs e, 有两个属性,一个是ExceptionObject,这个属性返回为截获异常的对象实例。还有一个属性是IsTerminating,这个属性告诉我们这 个异常是否会导致应用终止。这里需要说明的是,对于.Net1.1 和 .Net2.0及以上,情况是不一样的,.Net1.1 只有在主线程中的未捕获异常才会终止应用程序,而.Net2.0及以上版本则是始终终止应用程序。如果不终止应用程序,而是有CLR 将当前异常消化,系统的运行状态很可能不可控,最后可能会发生更大的故障,所以.Net2.0以后,对于所有未捕获异常,一律终止当前应用。这样看来,对 于.net2.0以上的应用似乎我们截获未捕获异常已经毫无意义,其实不然。通过截获为未捕获异常,我们可以记录下程序是再哪里产生这种未捕获异常的,以 便程序的开发者改进程序。我们也可以在当前应用退出前为系统做一些其他的保护工作,比如备份数据,告警提示等等。
下面我们来看看三种常见的.Net应用分别如何来截获未捕获异常。
- 控制台应用
首先为当前AppDomain 添加 UnhandledExceptionEventHandler
AppDomain.CurrentDomain.UnhandledException +=
new UnhandledExceptionEventHandler(UnhandledExceptionEventHandler);
再添加事件响应函数
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using (System.IO.FileStream fs = new System.IO.FileStream( @" c:/testme.log " ,
System.IO.FileMode.Append, System.IO.FileAccess.Write))
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using (System.IO.StreamWriter w = new System.IO.StreamWriter(fs,
System.Text.Encoding.UTF8))
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现在我们就可以截获未捕获异常了
下面是完整的测试代码:
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using (System.IO.FileStream fs = new System.IO.FileStream( @" c:/testme.log " ,
System.IO.FileMode.Append, System.IO.FileAccess.Write))
{
using (System.IO.StreamWriter w = new System.IO.StreamWriter(fs,
System.Text.Encoding.UTF8))
{
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AppDomain.CurrentDomain.UnhandledException +=
new UnhandledExceptionEventHandler(UnhandledExceptionEventHandler);
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程序运行后记录下日志如下
System.DivideByZeroException: Attempted to divide by zero.
at TestCosole.Program.TestRaiseException.Finalize()
- WinForm
WinForm 应用通过 Application.ThreadException 事件来截获未捕获异常
详见 园子里面另一篇博客,这里就不再冗诉。
- Asp.net
ASP.NET 应用和前两种应用有所不同,ASP.NET 一般在后台线程或者线程池中产生未捕获异常,才会导致W3WP.exe终止,并在事件查看器中产生一条类似下面内容的事件:EventType clr20r3, P1 w3wp.exe, P2 6.0.3790.1830, P3 42435be1, P4 app_web_ncsnb2-n, P5 0.0.0.0, P6 440a4082, P7 5, P8 1, P9 system.nullreferenceexception, P10 NIL.
要截获ASP.NET 的未捕获异常,我们需要为每个应用程序域安装事件钩子
这个过程需要分两步完成:
首先创建一个实现IHttpModule接口的类
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using (System.IO.FileStream fs = new System.IO.FileStream( @" c:/testme.log " ,
System.IO.FileMode.Append, System.IO.FileAccess.Write))
{
using (System.IO.StreamWriter w = new System.IO.StreamWriter(fs, System.
Text.Encoding.UTF8))
{
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第二步:
修改web.config
在 system.web 段中加入
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完成这两步后,你的ASP.NET 应用就可以截获未捕获异常了。
下面是测试代码
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System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(TestMe),
null);
}
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按下Button1后,w3wp.exe被终止,testme.log 中记录下了异常信息如下:
System.IndexOutOfRangeException: Index was outside the bounds of the array.
at _Default.TestMe(Object state) in c:"ApolloWorkFolder"test"laboratory
"TestWebSite"Default.aspx.cs:line 21
at System.Threading._ThreadPoolWaitCallback.WaitCallback_Context(Object state)
at System.Threading.ExecutionContext.runTryCode(Object userData)
at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(
TryCode code, CleanupCode backoutCode, Object userData)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext,
ContextCallback callback, Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext,
ContextCallback callback, Object state)
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallbackInternal(
_ThreadPoolWaitCallback tpWaitCallBack)
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback(Object state)。