Why is .NET exception not caught by try/catch block?

Question

I\'m working on a project using the ANTLR parser library for C#. I\'ve built a grammar to parse some text and it works well. However, when the parser comes across an illeg

Answer 1

I traced through the external assembly with Reflector and found no evidence of threading whatsoever.

You can't find any threading does not mean there is no threading

.NET has a 'thread pool' which is a set of 'spare' threads that sit around mostly idle. Certain methods cause things to run in one of the thread pool threads so they don't block your main app.

The blatant examples are things like ThreadPool.QueueUserWorkItem, but there are lots and lots of other things which can also run things in the thread pool that don't look so obvious, like Delegate.BeginInvoke

Really, you need to do what kibbee suggests.

Answer 2

I'm with @Shaun Austin - try wrapping the try with the fully qualified name

catch (System.Exception)

and see if that helps.Does the ANTLR doc say what Exceptions should be thrown?

Answer 3

Personally I'm not convinced by the threading theory at all.

The one time I've seen this before, I was working with a library which also defined Exception and the usings I had meant that the actual Catch was referring to a different "Exception" type (if it had been fully qualified it was Company.Lib.Exception but it wasnt because of the using) so when it came to catching a normal exception that was being thrown (some kind of argument exception if I remember correctly) it just wouldn't catch it because the type didn't match.

So in summary, is there another Exception type in a different namespace that is in a using in that class?

EDIT: A quick way to check this is make sure in your catch clause you fully qualify the Exception type as "System.Exception" and give it a whirl!

EDIT2: OK I've tried the code and concede defeat for now. I'll have to have another look at it in the morning if no one has come up with a solution.

Answer 4

Oh and in reference to what Kibbee said; if you select Debug|Exceptions in VS and just click all the boxes in the 'thrown' column it should pick everything up AFAIK as a 'first chance exception', i.e. VS will indicate when the exception is about to be processed by everything else and break on the relevant code. This should help with debugging.

Answer 5

Hmm, I don't understand the problem. I downloaded and tried your example solution file.

An exception is thrown in TimeDefLexer.cs, line 852, which is subsequently handled by the catch block in Program.cs that just says Handled exception.

If I uncomment the catch block above it, it will enter that block instead.

What seems to be the problem here?

As Kibbee said, Visual Studio will stop on exceptions, but if you ask it to continue, the exception will get caught by your code.

Answer 6

I agree with Daniel Auger and kronoz that this smells like an exception that has something to do with threads. Beyond that, here are my other questions:

1. What does the complete error message say? What kind of exception is it?
2. Based on the stack trace you've provided here, isn't the exception thrown by you code in TimeDefLexer.mTokens()?