Rethrown Exception's Original Location

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Hello. I'm reading through the book called "CLR via C#". In Exceptions part, i have stumbled into this part i can't understand. Apparently the code below is how some programmers handle the issue of lost original exception point in unhandled exceptions:

C#

private void SomeMethod() {
 Boolean trySucceeds = false;
 try {
 ...
 trySucceeds = true;
 }
 finally {
 if (!trySucceeds) { /* catch code goes in here */ }
 }
}

I know finally block finishes first before Unhandled Exception pops up, but i don't understand how does it accomplish preserving original exception point. Any ideas?

Thanks in advance.

Posted 30-Mar-15 21:05pm

YourAverageCoder

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Herman<T>.Instance 31-Mar-15 3:13am

Did you make a small app to test the situation? Did you debug the code? That should give you a learning curve in your question.

Sinisa Hajnal 31-Mar-15 3:41am

Why not simply have catch with single throw statement which re-throws original exception with location preserved?

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Fredrik Bornander · Accepted Answer · 2015-03-30T21:43:00

If I recall the book correctly, that code is supposed to work around an issue in the way the CLR is implemented on Windows. Even though the CLR will know the full stack trace if you rethrow an exception this way;

C#

void SomeMethod() {
  try {
     // Do something that may throw
  }
  catch {
     // caught it, do something and then re-throw
     throw;
  ]
}

Windows will create a new stack frame from the re throw point. This isn't an issue if you catch and log the exception, as that will give you the correct stack trace, but if it crashes the application (because it's un-handled) and you need to use something like windbg to inspect the crash dump, the original originating point of the exception will be lost.

In most cases you don't need to worry about this, it's often better just to add an uncaught exception handler that logs the exception and it's stack trace, that's easier to use as a basis for trouble shooting than windbg (or at least, it often is).

Hope this helps,
Fredrik