Reentrancy error

[Gavin-Williams]

I keep seeing this error...

Exception thrown at 0x00007FFA02AC7F7A (KernelBase.dll) in DemoWinUI.exe: WinRT originate error - 0x80004005 : 'Reentrancy was detected in this XAML application. Use a debugger to locate the reentrant code and, if necessary, move that code to an asynchronous event handler. Press OK to exit the application.'.
Microsoft.UI.Xaml.dll!00007FF8D22EE22D: 8000FFFF - E_UNEXPECTED
Unhandled exception at 0x00007FF8D23911F5 (Microsoft.ui.xaml.dll) in DemoWinUI.exe: 0xC000027B: An application-internal exception has occurred (parameters: 0x000001E18D957080, 0x0000000000000001).

I'm rendering a spinning cube with DirectX 12 (Vortice), here's my CompositionTarget_Rendering method...

    private void CompositionTarget_Rendering(object? sender, object e)
    {
        if (Renderer.State != Renderer.ExecutionState.ShuttingDown)
            Renderer.Invoke();       
        XamlFps.Text = Renderer?.FpsCounter.Reading.ToString();
    }

I can trigger the reentracy error and crash by mousing over the window. Is this my fault?

[Gavin-Williams]

So, I remember that sometimes the CompositionTarget_Rendering method would trigger multiple times in a frame. I remember using a check in UWP to catch those cases.

Copilot says that updating the text can be an issue, I don't think that is the issue here, but anyway, I've changed the text update code to...

        var fps = Renderer?.FpsCounter.Reading.ToString();
        _ = XamlFps.DispatcherQueue.TryEnqueue(() =>
        {
            XamlFps.Text = fps;
        });

I still see the reentracy issue. Execution is breaking on this line...

    public void WaitPresentCompleted()
   {
       //Debug.WriteLine("WaitPresentCompleted | Value = " + Value_PresentCompleted);
       if (Fence_PresentCompleted.CompletedValue < Value_PresentCompleted)
       {
           Fence_PresentCompleted.SetEventOnCompletion(Value_PresentCompleted, Event_PresentCompleted);
           Event_PresentCompleted.WaitOne(); // <----- Break here
       }
       Value_PresentCompleted++;
   }

I see Dx11 programs always use the Xaml rendering method - I guess with Dx12 we can't do that anymore? I just don't know how to solve this. This issue has been showing up over the past few days while I struggled with putting rendering on it's own thread. I just couldn't work it out (issues with fencing - not being able to prevent different back-buffers from being hit). I've reverted to just doing rendering on the main thread. So just sticking to one thread for the moment, how do I address this issue?

[Gavin-Williams]

I guess the solution is obvious - don't use the CompositionTarget_Rendering method. Though I'm not sure what it's for then.