Repository navigation
[BUG] DarlingViewer crash when trying to View Stored Plan for High Impact Queries #2825
Description
Component
Darling
Performance Monitor Version
3.6.0
SQL Server Version
2019 - 2025
Windows Version
windows server 2025
Describe the Bug
When trying to right click a query in the High Impact Queries in FinOps and then choose "View Stored Plan", the GUI crashes and shuts down.
Steps to Reproduce
Open the app
Click FinOps
Click High Impact
Wait for High Impact Queries to be shown in the list.
Right click the topmost query and choose "View Stored Plan"
Wait to see the GUI shut down
Expected Behavior
Stored Plan is shown
Actual Behavior
Application crashes
Error Messages / Log Output
From the view Log in the application after it has been started again I find the following:
2026-09-03 10:26:35.039 [ERROR] [App] Unhandled UI exception | InvalidOperationException: Cannot call StartAt when content generation is in progress.
2026-09-03 10:26:35.080 [ERROR] [App] Stack: at System.Windows.Controls.ItemContainerGenerator.System.Windows.Controls.Primitives.IItemContainerGenerator.StartAt(GeneratorPosition position, GeneratorDirection direction, Boolean allowStartAtRealizedItem)
at System.Windows.Controls.Panel.AddChildren(GeneratorPosition pos, Int32 itemCount)
at System.Windows.Controls.Panel.OnItemsChangedInternal(Object sender, ItemsChangedEventArgs args)
at System.Windows.Controls.Panel.OnItemsChanged(Object sender, ItemsChangedEventArgs args)
at System.Windows.Controls.ItemContainerGenerator.OnItemAdded(Object item, Int32 index)
at System.Windows.Controls.ItemContainerGenerator.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
at System.Windows.WeakEventManager.DeliverEventToList(Object sender, EventArgs args, ListenerList list)
at System.Collections.Specialized.CollectionChangedEventManager.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
at System.Windows.WeakEventManager.DeliverEventToList(Object sender, EventArgs args, ListenerList list)
at System.Collections.Specialized.CollectionChangedEventManager.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
at System.Windows.Controls.ItemCollection.Insert(Int32 insertIndex, Object insertItem)
at PerformanceMonitor.Ui.StandalonePlanViewerController.AddNewEmptyPlanSubTab()
at PerformanceMonitor.Ui.StandalonePlanViewerController.<EnsureInitialized>b__4_0(Object _, SelectionChangedEventArgs _)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.TabControl.OnSelectionChanged(SelectionChangedEventArgs e)
at System.Windows.Controls.Primitives.Selector.SelectionChanger.SelectJustThisItem(ItemInfo info, Boolean assumeInItemsCollection)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetCurrentValueInternal(DependencyProperty dp, Object value)
at System.Windows.Controls.TabControl.OnGeneratorStatusChanged(Object sender, EventArgs e)
at System.Windows.Controls.ItemContainerGenerator.SetStatus(GeneratorStatus value)
at System.Windows.Controls.ItemContainerGenerator.Generator.System.IDisposable.Dispose()
at System.Windows.Controls.Panel.GenerateChildren()
at System.Windows.Controls.Panel.get_InternalChildren()
at System.Windows.Controls.Primitives.TabPanel.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Control.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.ContentPresenter.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Border.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.ContextLayoutManager.UpdateLayout()
at System.Windows.Controls.TabItem.OnPreviewGotKeyboardFocus(KeyboardFocusChangedEventArgs e)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.KeyboardDevice.TryChangeFocus(DependencyObject newFocus, IKeyboardInputProvider keyboardInputProvider, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
at System.Windows.Input.KeyboardDevice.Focus(DependencyObject focus, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
at System.Windows.Input.KeyboardDevice.Focus(IInputElement element)
at System.Windows.UIElement.Focus()
at System.Windows.Controls.TabItem.SetFocus()
at System.Windows.Controls.TabControl.OnSelectionChanged(SelectionChangedEventArgs e)
at System.Windows.Controls.Primitives.Selector.SetSelectedHelper(Object item, FrameworkElement UI, Boolean selected)
at System.Windows.Controls.Primitives.Selector.NotifyIsSelectedChanged(FrameworkElement container, Boolean selected, RoutedEventArgs e)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.TabItem.OnIsSelectedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at PerformanceMonitor.Darling.Viewer.MainWindow.OpenStoredPlanInPlanViewer(String planXml, String label, String queryText)
at PerformanceMonitor.Darling.Viewer.FinOpsTab.FinOpsViewPlan_Click(Object sender, RoutedEventArgs e)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.MenuItem.InvokeClickAfterRender(Object arg)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
2026-09-03 10:26:35.081 [ERROR] [App] Unhandled domain exception | InvalidOperationException: Cannot call StartAt when content generation is in progress.
2026-09-03 10:26:35.082 [ERROR] [App] Stack: at System.Windows.Controls.ItemContainerGenerator.System.Windows.Controls.Primitives.IItemContainerGenerator.StartAt(GeneratorPosition position, GeneratorDirection direction, Boolean allowStartAtRealizedItem)
at System.Windows.Controls.Panel.AddChildren(GeneratorPosition pos, Int32 itemCount)
at System.Windows.Controls.Panel.OnItemsChangedInternal(Object sender, ItemsChangedEventArgs args)
at System.Windows.Controls.Panel.OnItemsChanged(Object sender, ItemsChangedEventArgs args)
at System.Windows.Controls.ItemContainerGenerator.OnItemAdded(Object item, Int32 index)
at System.Windows.Controls.ItemContainerGenerator.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
at System.Windows.WeakEventManager.DeliverEventToList(Object sender, EventArgs args, ListenerList list)
at System.Collections.Specialized.CollectionChangedEventManager.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
at System.Windows.WeakEventManager.DeliverEventToList(Object sender, EventArgs args, ListenerList list)
at System.Collections.Specialized.CollectionChangedEventManager.OnCollectionChanged(Object sender, NotifyCollectionChangedEventArgs args)
at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
at System.Windows.Controls.ItemCollection.Insert(Int32 insertIndex, Object insertItem)
at PerformanceMonitor.Ui.StandalonePlanViewerController.AddNewEmptyPlanSubTab()
at PerformanceMonitor.Ui.StandalonePlanViewerController.<EnsureInitialized>b__4_0(Object _, SelectionChangedEventArgs _)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.TabControl.OnSelectionChanged(SelectionChangedEventArgs e)
at System.Windows.Controls.Primitives.Selector.SelectionChanger.SelectJustThisItem(ItemInfo info, Boolean assumeInItemsCollection)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetCurrentValueInternal(DependencyProperty dp, Object value)
at System.Windows.Controls.TabControl.OnGeneratorStatusChanged(Object sender, EventArgs e)
at System.Windows.Controls.ItemContainerGenerator.SetStatus(GeneratorStatus value)
at System.Windows.Controls.ItemContainerGenerator.Generator.System.IDisposable.Dispose()
at System.Windows.Controls.Panel.GenerateChildren()
at System.Windows.Controls.Panel.get_InternalChildren()
at System.Windows.Controls.Primitives.TabPanel.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Control.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.ContentPresenter.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Border.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
at System.Windows.UIElement.Measure(Size availableSize)
at System.Windows.ContextLayoutManager.UpdateLayout()
at System.Windows.Controls.TabItem.OnPreviewGotKeyboardFocus(KeyboardFocusChangedEventArgs e)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.KeyboardDevice.TryChangeFocus(DependencyObject newFocus, IKeyboardInputProvider keyboardInputProvider, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
at System.Windows.Input.KeyboardDevice.Focus(DependencyObject focus, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
at System.Windows.Input.KeyboardDevice.Focus(IInputElement element)
at System.Windows.UIElement.Focus()
at System.Windows.Controls.TabItem.SetFocus()
at System.Windows.Controls.TabControl.OnSelectionChanged(SelectionChangedEventArgs e)
at System.Windows.Controls.Primitives.Selector.SetSelectedHelper(Object item, FrameworkElement UI, Boolean selected)
at System.Windows.Controls.Primitives.Selector.NotifyIsSelectedChanged(FrameworkElement container, Boolean selected, RoutedEventArgs e)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.TabItem.OnIsSelectedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at PerformanceMonitor.Darling.Viewer.MainWindow.OpenStoredPlanInPlanViewer(String planXml, String label, String queryText)
at PerformanceMonitor.Darling.Viewer.FinOpsTab.FinOpsViewPlan_Click(Object sender, RoutedEventArgs e)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.MenuItem.InvokeClickAfterRender(Object arg)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.DispatcherOperation.InvokeImpl()
at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.ProcessQueue()
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
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.Application.RunDispatcher(Object ignore)
at System.Windows.Application.RunInternal(Window window)
at PerformanceMonitor.Darling.Viewer.Program.Main(String[] args)
Screenshots
Additional Context
No response
Activity
ghauan commentedon Sep 3, 2026
Extra info: this happens both on the read-write viewer on the server running the Darling-service, and on read-only viewer on another VM.
Merge pull request #2829 from erikdarlingdata/feature/2825-planviewer…
erikdarlingdata commentedon Sep 3, 2026
Fixed in #2829 (merged to dev). The shared StandalonePlanViewerController auto-added a plan sub-tab from a SelectionChanged handler that WPF re-raised for the auto-selected '+' sentinel from INSIDE the inner TabControl's container generator during first-time realization; the mid-generation ItemCollection.Insert threw 'Cannot call StartAt when content generation is in progress' and crashed the app. The '+'-tab auto-add now defers off the generation pass while only the sentinel is present (first-time setup) and stays synchronous for a real user click, so the opener's own sub-tab renders - no duplicate tab, no reordering, no crash. Same shared fix covers Lite; the deprecated Dashboard's separate copy got the identical guard. Follow-up #2828 tracks a pre-existing handler-accumulation leak found alongside.
Fix erikdarlingdata#2825: defer the Plan Viewer "+"-tab auto-add out …
Fix erikdarlingdata#2828: subscribe Plan Viewer tab handler once in t…
Plan viewer: a screen-reader select on the + tab adds one sub-tab, an…