Exception "Collection was modified" in System.Windows.Input.StylusWisp on remote desktop

[Lumoryel]

Hi there,
got this exception today on a remote machine directly after connecting via windows remote desktop:

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.ValueCollection.Enumerator.MoveNext()
at System.Windows.Input.StylusWisp.WispLogic.OnTabletAdded(UInt32 wisptisIndex)
at System.Windows.Input.StylusWisp.WispLogic.HandleMessage(WindowMessage msg, IntPtr wParam, IntPtr lParam)
at System.Windows.SystemResources.InvalidateTabletDevices(WindowMessage msg, IntPtr wParam, IntPtr lParam)
at System.Windows.SystemResources.SystemThemeFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

We have a .NET Framework 4.8 WPF Program running in the background, the window was not visible at that moment.
Running on Windows 11 Pro.

[dipeshmsft]

Can you provide us a sample repro application ?

[Lumoryel]

Unfortunately not, it happened just one time when I connected via remote desktop.
Could it be a (threading?)-Problem in WispLogic.OnTabletAdded ?

[lindexi]

@Lumoryel I review the code and I find all the __penContextsMap in the lock by __penContextsLock. This at least shows that this code is thread safe.

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Wisp/WispLogic.cs

Lines 3336 to 3339 in 368f0e8

	foreach (PenContexts contexts in __penContextsMap.Values)
	{
	contexts.AddContext(tabletIndex);
	}

[Lumoryel]

@lindexi You're right. I can't find code that modifies __penContextsMap without a lock.

By the way I saw that not all methods are in lock(__penContextsLock) when accessing __penContextsMap e.g. via TryGetValue().
Additionally, RefreshTablets() is enumerating the __penContextsMap without locking (e.g. called from PostProcessInput() ).

But this shouldn't be the cause for the exception.

Sure that this source code also applies for .net framework 4.8 ?
When I search in referencesource, I can't find the Stylus classes.

[miloush]

How about this one

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Stylus/Wisp/WispLogic.cs

Line 1365 in 368f0e8

RefreshTablets();

@Lumoryel is correct that this enumerates the collection without locking from PostProcessInput. This would cause the exception when you try to modify it elsewhere. EDIT: Nevermind, I see what you are saying now, competing foreach would not cause this stack, however, it would still throw if PostProcessInput calls RefreshTablets() and during that the collection is modified (even if under lock). I don't see any out-of-lock modifications either.

You can use ILSpy to check whether the assemblies you are using on that machine contain the code you are looking for, both 3.0 and latest version of PresentationCore do seem to include these locks though.

If you can reproduce, time travel would be helpful.

[singhashish-wpf]

@Lumoryel Do we have any more inputs on this? A TTD trace or some reliable sample repro?

[Lumoryel]

@singhashish-wpf I never saw this bug again.
What I noticed meanwhile:
On Windows 11, when you run a .NET Framework 4.8 targeted program, it actually runs Framework 4.8.1 code while on windows 10 it runs 4.8 code.

Actually I'm confused about where to look for 4.8 and 4.8.1 code?

(I had this problem here with a 4.8 framework application: #6319)

[GSonofNun]

Just had this happen with our application. The user RDP'd from their laptop (with touch/pen support) to their desktop (without pen support) where our aplication was already running. Our app is using .NET 6, and both PCs are running Windows 11.

Unfortunately we don't have any good repro steps for it. Just wanted to mention another sighting

[GSonofNun]

I do have a minidump of the crash if it would be helpful.

[Tennyleaz]

Had this issue occurred once on my app, when a DisplayLink touch screen was removed from USB.
Using WPF and .net 4.7.2 on Windows 10.