Disconnect stale automation peers from UIA to fix memory leak in virtualized ItemsControls#11657
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Pull request overview
This PR addresses a memory leak in WPF UI Automation (UIA) for virtualized ItemsControl scenarios by explicitly disconnecting UIA providers for removed automation peers, allowing COM references held by UIA Core to be released and enabling GC of stale peers and their visual subtrees.
Changes:
- Added a helper to disconnect an
AutomationPeer’sElementProxyfrom UIA viaUiaDisconnectProvider. - Updated
UpdateChildrenInternalto disconnect removed children even when noStructureChangedlisteners are registered. - Added the required interop import to call into
UIAutomationCore.dll.
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| if (proxyWeakRef?.Target is ElementProxy proxy) | ||
| { | ||
| UiaDisconnectProvider(proxy); | ||
| } | ||
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| peer._elementProxyWeakReference = null; |
…ualized ItemsControls When a UIA client enumerates automation peers via FindAll, ElementProxy CCWs are created but never released, pinning managed peers and entire visual sub-trees in memory. This change disconnects removed peers in both UpdateChildrenInternal and EnsureChildren, breaking the reference chain so containers can be GC'd. Key changes: - DisconnectPeerFromUia defers UiaDisconnectProvider via Dispatcher.BeginInvoke to avoid calling it during UIA callbacks (re-entrancy unsafe). - proxy.ClearPeer() severs the ElementProxy->peer strong reference immediately, allowing the peer to become GC-eligible before the deferred call executes. - peer._children is nulled to break the chain from disconnected item peers to cached cell peers that root DataGridCell/DataGridRow containers. - EnsureChildren disconnects stale peers gated on _elementProxyWeakReference, making it allocation-free when no UIA client has walked the subtree. Fixes dotnet#11337 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Fixes #11337
Description
When UIA clients enumerate a virtualized ItemsControl (e.g. DataGrid), ElementProxy CCWs are created for each automation peer. Previously, when children were replaced (e.g. due to collection rebinding), the old peers were never disconnected from UIA Core. The COM references held by UIA kept the CCW ref count > 0, pinning the managed peers and their entire visual sub-trees in memory indefinitely.
This fix calls
UiaDisconnectProvideron removed children's ElementProxy CCWs duringUpdateChildrenInternal, causing UIA Core to release its COM references. This allows the CCW ref count to drop to zero so the managed peers can be garbage collected.Note: UIA clients may observe
ElementNotAvailableExceptionwhen accessing properties of stale elements after disconnection. This is standard UIA behavior that well-behaved clients already handle.Customer Impact
WPF applications using virtualized ItemsControl (e.g., DataGrid, ListView) that are exposed to UI Automation clients (screen readers, automated testing tools, accessibility inspectors) experience an unbounded memory leak of approximately 260 MB/min in the customer's repro scenario (200k-row DataGrid with periodic rebinding). The leak occurs because stale AutomationPeer instances are never disconnected from UIA Core - their ElementProxy CCW ref counts never reach zero, permanently pinning the managed peers and their visual sub-trees in memory. This leads to
OutOfMemoryExceptionand application crashes in long-running scenarios. Any application with accessibility enabled (which is the default when assistive technology or test automation is present) is affected.Regression
No.
Testing
Tested using the customer`s repro scenario:
Base line memory leak rate: +260 MB/min
With fix: +15.3 MB/min (94% reduction)
Risk
Low overall.
UpdateChildrenInternalinAutomationPeer.cs- a single code path that runs when automation children are replaced.UiaDisconnectProvideris the documented Windows API for this exact purpose — telling UIA Core to release COM references to providers that are no longer valid. This is the same mechanism used by other frameworks (e.g., WinForms) to manage automation peer lifetimes.UpdateChildrenInternaldetects removed children, which only happens when automation is active and the tree structure changes.FindAllcall may now receiveElementNotAvailableExceptionwhen accessing properties of disconnected elements. This is standard UIA contract behavior that well-behaved clients (including Narrator, NVDA, and JAWS) already handle. Poorly written test automation tools that do not catch this exception may surface errors they previously did not encounter.Microsoft Reviewers: Open in CodeFlow