Sometimes crashes Access with Access Violation Exception (0xc0000005)

[Indigo744]

Hello,

First let me say that this is a very useful library to bring better dialogbox to users. Thank you for your hard work!

I would like to report a quite hard to grasp issue.

This is a Microsoft Access 2024 64 bits, in French, on Windows 11 Pro.
The TaskDialog library is latest (v1.6 R2).

Lately, I have been having regular Ms Access crash with an Access Violation Exception (0xc0000005) when doing various interaction (clicking on buttons, selecting a new line...).

The following event is logged in the Application log (somes parts in French):

Nom de l'application défaillante : MSACCESS.EXE, version : 16.0.17932.20602, horodatage : 0x690d8376
Nom du module défaillant : VBE7.DLL, version : 0.0.0.0, horodatage : 0x66c8d2d7
Exception code: 0xc0000005
Fault offset: 0x0000000000381e5a
Identifiant du processus défaillant : 0x51EC
Heure de début de l'application défaillante : 0x1DC6CE2C7798BE6
Chemin de l'application défaillante : C:\Program Files\Microsoft Office\Root\Office16\MSACCESS.EXE
Chemin du module défaillant : C:\Program Files\Common Files\Microsoft Shared\VBA\VBA7.1\VBE7.DLL
ID du rapport : 98df9afd-4af7-4584-9cb9-31323f331660
Nom complet du package défaillant : 
Package défaillant – ID d'application relatif : 

I was never able to find the issue as it is seemingly in random. If I try the exact same action after restarting the app, it works flawlessly.
The issue can also happen on different machine.
This is quite maddening.

However, this week I observed 3 random crashes happening on a specific button. It is a custom button added in the Ms Access Ribbon, and the first thing it does is displaying a confirmation dialog using this TaskDialog library.

When the crashes occurred, the dialog was never displayed. That's why I believe the issue may come from this library.

Here is the Sub in question :

Public Sub Ribbon_OnClick(Control As IRibbonControl)
    If MsgBoxConfirm("...") Then
        ' Do something
    End If
End Sub

And here are the support functions used:

Public Function MsgBoxConfirm(Content As Variant, Optional ContentTitle As Variant = "", Optional icon As TDICONS = IDI_QUESTION, Optional DefaultButton As TDRESULT = TD_YES) As Boolean
    Dim TaskDialog As New cTaskDialog
    With TaskDialog
        .Init
        .Flags = TDF_ENABLE_HYPERLINKS Or TDF_EXEC_HYPERLINKS Or TDF_SIZE_TO_CONTENT
        .title = "Title"
        .ParenthWnd = GetParenthWnd

        .MainInstruction = ContentTitle
        .Content = Content

        .CommonButtons = TDCBF_YES_BUTTON Or TDCBF_CANCEL_BUTTON
        .DefaultButton = DefaultButton

        .title = "Confirmation"
        .IconMain = icon

        .ShowDialog

        MsgBoxConfirm = .ResultMain = TD_YES
    End With
    Set TaskDialog = Nothing
End Function

Function GetParenthWnd() As LongPtr
    GetParenthWnd = Application.hWndAccessApp
    If Application.CurrentObjectType = acForm Then
        If IsFormDialog(Screen.ActiveForm) Then
            GetParenthWnd = Screen.ActiveForm.hwnd
        End If
    End If
End Function

Public Function IsFormDialog(frm As Form) As Boolean
    Dim hwnd As LongPtr
    Dim lngStyle As LongPtr
    hwnd = frm.hwnd
    lngStyle = GetWindowLong(hwnd, GWL_EXSTYLE)
    IsFormDialog = CBool((lngStyle And WS_EX_DLGMODALFRAME) = WS_EX_DLGMODALFRAME)
End Function

I don't remember having this kind of crashes when we used Access 2019 32 bits. Not on this button anyway.

I noticed this comment in the mTDHelper.bas file:

Public Sub MagicalTDInitFunction()
        'The trick is a GENIUS!
    'He identified the bug in VBA64 that had been causing the crashing.
    'As if by magic, calling this from Class_Initialize resolves the problem.
End Sub

I couldn't find any information on theses crashes (or how any real explanation of this "genius trick") but I though it may be related?

Thank you for your time and any help you can provide on this matter! 😸

[fafalone]

The bug in question iirc didn't affect Access and crashed 100% of the time, but you can find details on VBForums: https://www.vbforums.com/showthread.php?898424-Class-module-callback-method-crashing-in-VBAx64

It's going to be hard to fix if there's no way to reproduce or even know for sure it's the class... If this is related to the class, the most likely culprit is something about the callback/subclassing... You could disable it and see if the crashes go away; that would at least narrow it down a bit... in cTaskDialog.cls in the ShowDialog function comment out uTDC.pfCallback = tdFARPROC(AddressOf TaskDialogCallbackProc) (line 2474).

[Indigo744]

Thanks for your answer. The link is quite interesting, even if not related to the issue at hand.

If I disable the callback, what exactly will no longer work? I use this class extensively throughout the codebase for various purpose.

[fafalone]

It's to help narrow things down so the issue can be identified and fixed, not a permanent solution. Events wouldn't work; if you've declared one module-level WithEvents like Private WithEvents cTD As cTaskDialog, then events like cTD_DialogCreated wouldn't fire. Hyperlinks wouldn't work. Again, it's just to confirm it's the class and start to identify what part.

[Indigo744]

I don't have WithEvents, but I do have some dialog with hyperlink.

I see there is another callback line 3280 .pfCallback = tdFARPROC(AddressOf TaskDialogCallbackProc), should this one also be commented out?

[fafalone]

You can but that function can't be reached unless you use multi-page dialogs which require the original callback and events.

[Indigo744]

Alright thanks.

It can take quite some time before a crash occurs... I'll let you know if I see an improvement.