Question

We’re having problems with Windows silently eating exceptions and allowing the application to continue running, when the exception is thrown inside the message pump. For example, we created a test MFC MDI application, and overrode OnDraw:

void CTestView::OnDraw(CDC* /*pDC*/)
{
    *(int*)0 = 0; // Crash

    CTestDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    if (!pDoc)
        return;

    // TODO: add draw code for native data here
}

You would expect a nasty error message when running the application, but you actually get nothing at all. The program appears to be running perfectly well, but if you check the output window you will see:

First-chance exception at
0x13929384 in Test.exe:
0xC0000005: Access violation writing
location 0x00000000.
First-chance exception at 0x77c6ee42
in Test.exe: 0xC0150010: The
activation context being deactivated
is not active for the current thread
of execution.

I know why I’m receiving the application context exception, but why is it being handled silently? It means our applications could be suffering serious problems when in use, but we’ll never know about it, because our users will never report any problems.

Answer 1

After browsing similar questions I stumbled across this answer:
OpenGL suppresses exceptions in MFC dialog-based application

“Ok, I found out some more information
about this. In my case it’s windows 7
that installs
KiUserCallbackExceptionHandler as
exception handler, before calling my
WndProc and giving me execution
control. This is done by
ntdll!KiUserCallbackDispatcher. I
suspect that this is a security
measure taken by Microsoft to prevent
hacking into SEH.

The solution is to wrap your wndproc
(or hookproc) with a try/except
frame.”

I’ve filed a bug report with Microsoft, you can see their response here:
http://connect.microsoft.com/VisualStudio/feedback/details/550944/hardware-exceptions-on-x64-machines-are-silently-caught-in-wndproc-messages

From Microsoft:

Thanks for the report. I’ve found out that this is a Windows issue,
and there is a hot fix available. Please see
http://support.microsoft.com/kb/976038 for a fix that you can install
if you wish.