[1.18+] On Windows 10, Terminal reserves ~15 MB of memory per window opened at the same time

[zadjii-msft]

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Note: 📌 Pinned comment: #15384 (comment)

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This is from me deploying to a Win10 19041 VM.

Closed a second window, then hovered over the first. At some point got:

>	Windows.UI.Xaml.Controls.dll!winrt::throw_hresult(const winrt::hresult result) Line 4524	C++
 	[Inline Frame] Windows.UI.Xaml.Controls.dll!winrt::check_hresult(winrt::hresult) Line 4612	C++
 	Windows.UI.Xaml.Controls.dll!winrt::impl::consume_Windows_UI_Xaml_IDependencyObject<AcrylicBrush>::GetValue(const winrt::Windows::UI::Xaml::DependencyProperty & dp) Line 1045	C++
 	[Inline Frame] Windows.UI.Xaml.Controls.dll!AcrylicBrushProperties::AlwaysUseFallback() Line 150	C++
 	Windows.UI.Xaml.Controls.dll!AcrylicBrush::UpdateAcrylicBrush() Line 996	C++
    ...

This one's a hard failfast that can't be continued. Window also seems to be in a normal state? In a normal _messagePump?

This happens every time I hover the split button after closing another window on Windows 10, but not on Windows 11.

Originally posted by @zadjii-msft in #15364 (comment)

[zadjii-msft]

Relevant threads:

• MSFT:31861775
• MSFT:32109540
• os.2020!6512498

Basically, when we close a DesktopWindowXamlSource, it calls to Windows_UI_Xaml!DirectUI::MetadataAPI::Reset, which resets the XAML metadata provider for the process. So, closing one DWXS on one thread fucks all the other threads with XAML.

This was fixed in Windows 11 by os.2020!5837001. That wasn't backported to Windows 10. We may be in a bad spot.

• Not release 1.18 for Windows 10, until that's fixed?
• Hold the release entirely until we find some workaround?
• Manually disable process model v3 on Windows 10 (is that even possible?)
• Leak the DesktopWindowsXamlSource (ew)
• Use some sort of threadpool to hold on to expired windows, and re-use them for subsequent windows (this will still consume extra memory, but only up to "max number of simultaneous windows" instead of "the total number of windows opened")
• Ship to Win11. Hold off on shipping to win10 until we do the threadpool thing?

[zadjii-msft]

After #15397, closing a window on Win10 will simply leak the window. This will result in a ~15 MB memory leak, which is Bad but less bad than full on crashing.

I'm working on a way to re-use old threads. That'll cause the leak to be scaled on N="max number of simultaneously open windows" rather than M="total number of closed windows over the life of the Terminal process"