JIT Debugging hiding bug in C# app - debugging

Question

I have an application that works fine under visual studio.
However, when I run it stand-alone, a certain operation which throws an exception isn't handled. (The exception is expected, but it's correctly handled under VS.)
I added a line to my machine.config to enable JIT debugging, to try and locate the problem, but I then could not recreate the bug (the exception was handled correctly). Deleting the line causes the bug to come back.
How should I start looking for the cause?
The relevant parts (I believe) of my code (edited to remove extraneous detail) are at http://pastebin.com/i2zLCTn5.

Answer 1

Some suggestions that may affect how your code is behaving in the different environment of Visual Studio:
Stop Visual Studio turning off the JIT Optimizer when you run your program under Visual Studio.There's an option called "Suppress JIT optimization on module load"...you want to try changing that to be NOT ticked.
For more details on what the option does see here:
http://msdn.microsoft.com/en-us/library/ms241594.aspx
Turn off the "hosting process" ...http://msdn.microsoft.com/en-us/library/ms185330(v=vs.80).aspx
Run the Program, then "Attach to Process" (it then won't be in a hosting process, and the modules will have been loaded and JIT optimized).
In the Exceptions dialog tick the "Thrown" check box of the Exception that is being eated/handled....so that you can track down who is handling it and why. You will need to install the NET Framework Sourcecode if the Exception is being handled there so that you can see the details.
You could have a try at running it under WinDBG instead (it may behave differently as you then won't be running under a hosting process i.e. .vshost)....make sure you have the extension DLL PSSCOR4 (if using .NET 4) so that you can make sense of things.

Answer 2

So, I discovered - or rather, a friend explained - the cause of this problem:
You cannot catch exceptions across threads when JIT debugging is disabled, even if execution appears to flow correctly.
The exception was being thrown in a Form.Closing event handler:
form.Closing += new delegate
{
switch(form.DialogResult)
{
case DialogResult.OK:
// do stuff;
break;
case DialogResult.Cancel:
throw new AbortOperationException();
}
}
// ...
try
{
mainForm.Invoke(new Function<Form, DialogResult>(form.ShowDialog), mainWindow);
}
catch (AbortOperationException)
{
// handle abort
}
The solution was to refactor slightly to eliminate the throw:
form.Closing += new delegate
{
if (form.DialogResult == DialogResult.OK)
{
// do stuff
}
}
// ...
var result = (DialogResult)mainForm.Invoke(new Function<Form, DialogResult>
if (result == DialogResult.Cancel)
{
// handle abort
}