ColorPicker: Crash in XAML islands when exiting app

[sylveon]

Describe the bug
When using ColorPicker in XAML islands, if the app is exited within a short timespan of tearing down a XAML island (or directly after), it will cause an access violation in Windows.UI.Xaml.dll.

Steps to reproduce the bug

1. Create a new blank WPF .NET Framework app.
2. Add the Microsoft.Toolkit.Wpf.UI.XamlHost NuGet package.
3. Add a project reference to the UniversalApiContract winmd from the Windows SDK.
4. Add an app manifest to the app, and within <compatibility> add <maxversiontested Id="10.0.19041.0" />
5. In MainWindow.xaml, write the following

   <Window x:Class="WpfApp2.MainWindow"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
           xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
           xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
           xmlns:local="clr-namespace:WpfApp2" xmlns:xamlhost="clr-namespace:Microsoft.Toolkit.Wpf.UI.XamlHost;assembly=Microsoft.Toolkit.Wpf.UI.XamlHost"
           mc:Ignorable="d"
           Title="MainWindow" Height="450" Width="800">
       <Grid>
           <xamlhost:WindowsXamlHost x:Name="host" />
       </Grid>
   </Window>

6. In MainWindow.xaml.cs's constructor, write this code

   public MainWindow()
   {
       InitializeComponent();
   
       var sp = new Windows.UI.Xaml.Controls.StackPanel
       {
           Background = new AcrylicBrush
           {
               BackgroundSource = AcrylicBackgroundSource.HostBackdrop,
               TintOpacity = 0
           },
           HorizontalAlignment = Windows.UI.Xaml.HorizontalAlignment.Stretch,
           VerticalAlignment = Windows.UI.Xaml.VerticalAlignment.Stretch
       };
       host.Child = sp;
   
       var button = new Windows.UI.Xaml.Controls.Button
       {
           Content = "Click me!",
           HorizontalAlignment = Windows.UI.Xaml.HorizontalAlignment.Center,
           VerticalAlignment = Windows.UI.Xaml.VerticalAlignment.Center
       };
   
       button.Click += (s, e) =>
       {
           Dispatcher.InvokeAsync(Close);
       };
   
       sp.Children.Add(button);
       sp.Children.Add(new ColorPicker());
   }

7. Launch the app.
8. Click the button

Expected behavior
The app should not crash

Screenshots

Version Info
NuGet package version:
[Microsoft.Toolkit.Wpf.UI.XamlHost 6.1.2]

Windows app type:

UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context
This also happens in my C++-based XAML islands app, so this is not an issue specific to the WCT WPF host, it just makes reproduction easier.

[Blinue]

Seems related to #7260?

My workaround is to manually load threadpoolwinrt.dll before Windows.UI.Xaml.dll is loaded.
https://github.com/Blinue/Magpie/blob/f1809baf11c6a62053285d8e3d08fc4922961c41/src/Magpie/XamlApp.cpp#L40-L44

[sylveon]

That sounds plausible, but unfortunately I'm unsure if we will be getting a fix :(

Maybe @namazso can quickly look at the crash and see if it's the same (but the stacktrace does look similar). @Scottj1s is there any chance to "backport" the fix from #7260, if the issue is the same? I can confirm this issue happens on both the WinUI 2 and system XAML color picker.

My current (terrible) workaround is calling TerminateProcess on my own process instead of gracefully exiting. An update to WinUI 2.8 with the fix would let me drop this nasty workaround.

[sylveon]

Bump, still an issue

[JesseCol]

Unfortunately, the WinUI team is currently spending its time on WinUI 3. To help with this focus, new bugs filed against WinUI 2 are closed in this repo unless they're a security issue or are business critical.

https://github.com/microsoft/microsoft-ui-xaml/blob/main/docs/contribution_handling.md#winui-2

[Blinue]

However, the issues of WinUI 3 have been virtually left unattended, and closing old issues is nothing but a self-deceiving act. I wonder how much you value the feedback from the community.