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Disappearing exceptions (x64)

Hopefully, this will help me the next time I bang my head against the wall trying to figure out why an application of mine is going crazy, but none of my error-handling code seems to be working.

The core threads that explain this are here:
The summary is this: If an exception is thrown on Windows x64 (Vista, Win2k3, Win2k8, Win7, etc.) and it hits a kernal-mode boundary, it will be dropped. Execution will continue at that point as if no exception had been thrown.

The simplest example is to create a new WinForm application and simply throw an exception from the OnLoad event. Not only will VS2008 not stop execution on that exception during debugging, but if you run it in "Release" mode, there will also be no trace of the exception.

In this case, your code (OnLoad) was ultimately called from something that executes in kernal-mode. When your exception propagates back up the stack, at the point it hits that boundary, the OS drops it. So execution then continues from the kernel-mode spot as if no exception was thrown---it acts as if the user-mode code had finished normally.

For me, since I don't currently know enough to say more, the simple solution is one of 2 things:
  1. Put all of my initialization code in the object's constructor instead of OnLoad.
  2. Have a try...catch inside OnLoad (or any other similar "black holes") and have a reliable logging/reporting mechanism in the "catch".
In practice, I don't think I'll ever use OnLoad again (in WinForm apps). And I hope to have this embedded in my brain deep enough that whenever I have an event-handler that's called from a kernel-mode thread, I'll know to treat it like a "black hole".

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