Application hangs on GC.Collect()

Describe the bug Some of our components use DirectX to fast render. On porting I found an issue that application hangs when I put such components in window`s content. After some researching I suggest that the issue relates to GC and interrop services. I prepared a synthetic sample to reproduce this issue. In my sample I create a descendant of SurfaceImageSource. After initialize component I query ISurfaceImageSourceNative interface from SurfaceImageSource.

On Window SizeChanged event I call GC.Collect(). When I run app and start resizing, the application hangs. If I run app under visual studio debugger, the application hangs with Visual Studio together.

If I comment GC.Collect (ln 43) or comment Marshal.GetObjectForIUnknown(pOut) line (ln 38), all works fine. There is why I suggested that issue relates to garbage collector and interrop services.

Steps to reproduce the bug

1. Compile and run attached project
2. Resize a window. Application will hang.
3. Comment line 43 (GC.Collect()) and run application again. All will work without errors.
4. Uncomment line 43 and comment lines 38-40. All will work good again.

App31.zip

Version Info

Windows 10 1903 (OS Build 18362.1082)

NuGet package version:

WinUI 3.0.0-preview2.200713.0

Windows app type:

UWP	Win32
No	Yes

Device form factor	Saw the problem?
Desktop	Yes

[alexserov]

After looking into the @BorzillaR sample, I see that the issue reproduces when the coreclr!RCWWalker::s_pGCManager field is not null. So I can hardly imagine how to work with native (COM) Windows runtime types since this may lead to application hanging.

To reproduce this, you can create a blank app from the Visual Studio template and replace the MainWindow ctor with the following code:

public MainWindow() {
    this.InitializeComponent();
    try {
        Marshal.GetObjectForIUnknown(ThisPtr);
    } catch { }
    GC.Collect();
}                

If you attach a debugger to the application, you’ll see a deadlock with the following call stack:

[0x0]   ntdll!NtWaitForAlertByThreadId + 0xc   
[0x1]   ntdll!RtlAcquireSRWLockExclusive + 0x17b   
[0x2]   Microsoft_UI_Xaml!DirectUI::ReferenceTrackerManager::ReferenceTrackingStarted + 0x3a   
[0x3]   coreclr!TrackerObjectManager::BeginReferenceTracking + 0x39   
[0x4]   coreclr!InteropLib::Com::BeginExternalObjectReferenceTracking + 0xb   
[0x5]   coreclr!Interop::OnGCStarted + 0x84   
[0x6]   coreclr!GCToEEInterface::GcStartWork + 0x31   
[0x7]   coreclr!WKS::gc_heap::garbage_collect + 0x23b   
[0x8]   coreclr!WKS::GCHeap::GarbageCollectGeneration + 0x1b0   
[0x9]   coreclr!WKS::GCHeap::GarbageCollectTry + 0x52   
[0xa]   coreclr!WKS::GCHeap::GarbageCollect + 0xc9   
[0xb]   coreclr!GCInterface::Collect + 0x56   
[0xc]   System_Private_CoreLib!System.GC.Collect()$##60003C0 + 0x23   

[stevenbrix]

Great, thanks @angelazhangmsft!

I’m going to close out this issue now that preview3 has been released. @BorzillaR, if you see this issue again, please respond and I will re-open. Thanks!