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Bug: folder-tree-dispatcher-thread-affinity #420
Description
- Work Mode: full-bug
Summary
The shared Outlook folder-tree service can invoke WpfDispatcherYield from a dispatcher-free worker after EmailDataMiner starts a cold cache build through Task.Run. Dispatcher.Yield then raises InvalidOperationException, and a fallback that only uses Task.Yield would not restore the required Outlook STA traversal contract.
Environment
- OS/version: Windows with Outlook VSTO runtime
- Application: TaskMaster Outlook add-in
- Trigger: Cold folder-tree cache build or refresh that reaches a deadline-controlled yield point
- Data source or fixture: Outlook folder hierarchy through the live COM adapter
Steps to Reproduce
- Start the email-mining path while the shared folder-tree cache requires a build or refresh.
EmailDataMiner.MineEmailsinvokesExtractOlFolderChunksthroughTask.Run.- The folder-tree reader reaches
WpfDispatcherYield.YieldAsyncafter the deadline clock requests a yield.
Expected Behavior
Live Outlook COM traversal and cooperative yielding remain on the captured Outlook STA dispatcher, and the caller receives a folder snapshot without a thread-affinity exception.
Actual Behavior
WpfDispatcherYield invokes Dispatcher.Yield(DispatcherPriority.Background) on a worker thread that has no current dispatcher. WPF raises InvalidOperationException indicating that the calling thread does not have a current Dispatcher.
Logs / Screenshots
- Captured stack evidence reviewed
- Snippet:
EmailDataMiner -> OutlookFolderTreeService -> FolderTreeSnapshotBuilder -> OutlookFolderHierarchyReader -> WpfDispatcherYield -> Dispatcher.Yield
Impact / Severity
- Blocker
- High
- Medium
- Low
Source
From: docs/features/potential/2026-08-04-folder-tree-dispatcher-thread-affinity.md
Activity
fix(folder-tree): prevent post-disposal UI mutations
fix(folder-tree): keep traversal on the Outlook STA dispatcher
fix(folder-tree): prevent post-disposal UI mutations
drmoisan commentedon Aug 8, 2026
Delivered by #422 (merged 2026-08-07, merge commit 0d85748) and the follow-up #423 (merged 2026-08-07, merge commit fb32b92). Neither PR body used a closing keyword, so this issue was not auto-closed.
Verified against
origin/main:UtilitiesCS/OutlookObjects/Folder/WpfDispatcherYield.csno longer callsDispatcher.Yield(). It resolves a dispatcher explicitly asDispatcher.FromThread(Thread.CurrentThread) ?? UtilitiesCS.UiThread.Dispatcher, posts a background-priorityInvokeAsync, and throwsInvalidOperationExceptionwith an actionable message when no dispatcher is available.WpfDispatcherYieldTests.YieldAsync_WithoutDispatcher_RemainsStrictandOutlookFolderTreeServiceConcurrencyTests.GetSnapshotAsync_WorkerOriginatedColdBuild_UsesCapturedStaDispatcher.Expected behavior in this issue (traversal and yielding remain on the captured Outlook STA dispatcher, no thread-affinity exception) is satisfied.
Closing as delivered.