#13 Crash when stopping message capturing

[Miroslav Policki]

Windows 10 64-bit
Window Detective 3.5.1

Unhandled exception at 0x00DC02B5 in Window Detective.exe: 0xC000041D: An unhandled exception was encountered during a user callback.

Window Detective.exe!00dc02b5() Unknown
[Frames below may be incorrect and/or missing, no symbols loaded for Window Detective.exe]
Window Detective.exe!00dd4943() Unknown
Window Detective.exe!00dc0496() Unknown
user32.dll!__InternalCallWinProc@20() Unknown
user32.dll!UserCallWinProcCheckWow() Unknown
user32.dll!DispatchClientMessage() Unknown
user32.dll!fnCOPYDATA@4() Unknown
ntdll.dll!KiUserCallbackDispatcher@12() Unknown
user32.dll!PeekMessageW() Unknown
Qt5Core.dll!61ceb778() Unknown
win32u.dll!_NtGdiSelectBitmap@8() Unknown
gdi32full.dll!SelectObjectImpl() Unknown
win32u.dll!_NtGdiDeleteObjectApp@4() Unknown
win32u.dll!_NtUserSetCursorIconData@16() Unknown
win32u.dll!_NtUserMessageCall@28() Unknown
user32.dll!InternalCallWinProc@20() Unknown
user32.dll!UserCallWinProcCheckWow() Unknown

Steps to reproduce:

1. Find a 32-bit window.
2. Start capturing messages.
3. Interact with the window to generate messages.
4. Click the Stop button in Window Detective.
5. Window Detective freezes, and after a few seconds, the Windows non-responsive application dialog pops up with an offer to close or debug. By clicking debug, I obtained the above stack trace in Visual Studio 2017.

For some reason, this is easier to do in some applications than others. I had no problem doing it in Thunderbird, but Skype required a bit more messages to get WD to crash.

[xtal256]

Thanks for the detailed information and stack trace.
I tried for a bit in Thunderbird but could not reproduce. Were you able to reproduce consistently, or was it intermittent?

[Miroslav Policki]

Yes, pretty consistently. I just restarted my computer and tried it twice (with Thunderbird), WD crashed both times.

[Miroslav Policki]

I've done some further testing and I think the trick is to generate so many messages that the application starts getting unresponsive. I've had a few tries where there weren't many messages captured, and WD didn't crash then.

[xtal256]

Yes, I suspected that might have been the case. I've definitely encountered bugs like this before, but they are difficult to debug because they are so rare/intermittent.

[Miroslav Policki]

Perhaps your CPU is faster than mine, so maybe you could trigger this bug more easily by running something CPU-heavy at the same time?

[xtal256]

Ah, I have been able to reproduce now. I was previously trying on Windows 7, but when I used Win 10 like you have, I was able to see it crash pretty quickly.

I only have my development tools on a Win 7 machine, so it will make debugging difficult. But I'll try to investigate some time soon.