How to debug this error when none of my code shows up in the stack?

Question

I'm sometimes getting the following error in my application:

Cannot use a DependencyObject that belongs to a different thread than its parent Freezable

I know how to solve this kind of error, but in that case I have no idea where it is happening, so I don't know what to fix... The exception's stack trace only contains .NET framework code, not my code (except the Main method):

   at System.Windows.Freezable.EnsureConsistentDispatchers(DependencyObject owner, DependencyObject child)
   at System.Windows.Freezable.OnFreezablePropertyChanged(DependencyObject oldValue, DependencyObject newValue, DependencyProperty property)
   at System.Windows.Freezable.OnFreezablePropertyChanged(DependencyObject oldValue, DependencyObject newValue)
   at System.Windows.Media.RenderData.PropagateChangedHandler(EventHandler handler, Boolean adding)
   at System.Windows.UIElement.RenderClose(IDrawingContent newContent)
   at System.Windows.Media.VisualDrawingContext.CloseCore(RenderData renderData)
   at System.Windows.Media.RenderDataDrawingContext.DisposeCore()
   at System.Windows.Media.DrawingContext.System.IDisposable.Dispose()
   at System.Windows.Media.RenderDataDrawingContext.Close()
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at MS.Internal.Helper.ArrangeElementWithSingleChild(UIElement element, Size arrangeSize)
   at System.Windows.Controls.ContentPresenter.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.WrapPanel.arrangeLine(Double v, Double lineV, Int32 start, Int32 end, Boolean useItemU, Double itemU)
   at System.Windows.Controls.WrapPanel.ArrangeOverride(Size finalSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at MS.Internal.Helper.ArrangeElementWithSingleChild(UIElement element, Size arrangeSize)
   at System.Windows.Controls.ItemsPresenter.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Control.ArrangeOverride(Size arrangeBounds)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Grid.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   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.RenderMessageHandler(Object resizedCompositionTarget)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext 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, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method, Object arg)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(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 MyApplication.App.Main() in E:\MyApplication\MyApplication\obj\Debug\App.g.cs:line 0
   at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

How can I track down the cause of this error ? Since the application is quite complex, manually checking all code that could be executed in another thread is not really an option...

Any advice would be appreciated !

Amalburga

That is the most impressive stack trace I have ever seen. – Admeasure

Answer 1

OK, I finally found the solution...

In one of my ViewModels, I was loading a list of brushes from the theme resources. In some situations, this ViewModel was used from a worker thread. I assumed the Freezables defined in XAML resource dictionaries were implicitly frozen, but apparently it's not the case... So I just needed to explicitly freeze them, and that fixed the problem.

Amalburga

Answer 2

Are you adding some UI controls dynamically on a background worker's DOwork handler?

Cadence

No, I'm not. The app follows the MVVM pattern, so I'm not manipulating the UI directly – Amalburga

I don't know, that's the point of my question... I'm looking for a way to get more information on that error, since the stack trace doesn't help in that case – Amalburga

see if this below post can help you as little info is on the questions. social.msdn.microsoft.com/forums/en-US/wpf/thread/… – Cadence

Actually I already found the solution, but it is indeed closely related to the post you mention. Thanks ;) – Amalburga

It is said that if ENDS is well than all is well too.. :) , Happy coding – Cadence

Answer 3

Have you tried Reflector Pro (there's a 14-day trial) ? You could ask it to generate debug info for WindowsBase.dll (where Freezable lives). Then you can put a breakpoint in the then part of the if statement in EnsureConsistentDispatchers. This should tell you which DependencyObjects are involved.

Are you creating DependencyObjects in another thread than the GUI thread ? Maybe in a callback method ?

Nanoid

I already tried it some time ago, so my trial period is over. Anyway, I should be able to use .NET Framework source stepping, but I've been unable to make it work so far... – Amalburga

I don't think I'm creating DOs in worker threads, but the code base is too large to check everything, so I'm not sure... – Amalburga