Wpf: NRE in Automation Peers

[clairernovotny]

.NET Core 3 preview 1

This is from my telemetry and resulted in an app crash.

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Automation.Peers.ItemAutomationPeer.GetNameCore()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.ContextLayoutManager.fireAutomationEvents()
   at System.Windows.ContextLayoutManager.UpdateLayout()
   at System.Windows.ContextLayoutManager.UpdateLayoutCallback(object arg)
   at System.Windows.Media.MediaContext+InvokeOnRenderCallback.DoWork()
   at System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   at System.Windows.Media.MediaContext.RenderMessageHandlerCore(object resizedCompositionTarget)
   at System.Windows.Media.MediaContext.AnimatedRenderMessageHandler(object resizedCompositionTarget)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, object args, int numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, Delegate callback, object args, int numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(object state)
   at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, object state)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, object state)
   at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, object args, int numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, Delegate callback, object args, int numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, object args, int numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(ref MSG msg)
   at System.Windows.Threading.Dispatcher.TranslateAndDispatchMessage(ref MSG msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.Run()
   at System.Windows.Application.RunDispatcher(object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at System.Windows.Application.Run()
   at PackageExplorer.App.Main()

[rladuca]

@miguep Will this be part of the remaining diff of desktop framework 4.8 to .NET Core 3?

[miguep]

@rladuca it is not part of that work

[clairernovotny]

I'm seeing a lot of these happen still, any reason this can't be looked at for 3.0?

Stack from earlier today:

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Automation.Peers.ItemAutomationPeer.GetNameCore()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdatePeer(object arg)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, object args, int numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, Delegate callback, object args, int numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(object state)
   at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, object state)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, object state)
   at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, object args, int numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, Delegate callback, object args, int numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, object args, int numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam)

[miguep]

We've observed this failure in .NET Framework as well and do not believe this is new to Core.

The WPF team's focus currently is on ensuring functional and performance parity between WPF in .NET Core and .NET Framework, once we meet that goal we can start looking into fixing some of these bugs

[weltkante]

Maybe quantify what "a lot" means. If the exception is rare in Desktop Framework and common in Core Framework that would still be a regression (in my opinion).

[MarkWatts12]

Seeing the same issue here. WPF (Framework 4.8 and 4.7.2) Same stack trace more or less. Can't find the culprit.

[eriove]

I suddenly started to get this every 2 seconds instead of once every other day of using the program. I turned on Framework source code debugging and the code fails on else if (item != null) in ItemAutomationPeer.GetNameCore()

Yes, that's a null reference exception on the line that checks if an object is null.

Not much else can be seen in the debugger. Here are the local variables

Most notably item is a MS.Internal.NamedObject with the value "{DependencyProperty.UnsetValue}".

I really can't understand why the code throws at that line. I suspect the symbols, binary and source are out of sync.