Fix UI-thread hang when resuming the target during launch#1596
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Pull request overview
This PR addresses a Visual Studio UI/SDM-thread hang during launch by decoupling AD7Engine.ContinueFromSynchronousEvent (ProgramCreate path) from blocking debugger I/O, while still preserving operation serialization behind the worker thread’s “running-op” slot.
Changes:
- Added
WorkerThread.PostAsyncOperationto dispatch anAsyncOperationwithout blocking the caller while still claiming the running-op slot. - Routed
AD7Engine.ContinueFromSynchronousEventlaunch-resume (ResumeFromLaunch) through the new non-blocking dispatch so it can returnS_OKimmediately. - Added an error-handler pathway for
PostAsyncOperationfaults and surfaced them via an engine callback.
Show a summary per file
| File | Description |
|---|---|
| src/MIDebugEngine/Engine.Impl/OperationThread.cs | Introduces PostAsyncOperation and error-handler plumbing for async operations. |
| src/MIDebugEngine/AD7.Impl/AD7Engine.cs | Stops blocking the UI thread on ResumeFromLaunch by posting it asynchronously and handling failures via callback. |
Review details
- Files reviewed: 2/2 changed files
- Comments generated: 2
- Review effort level: Low
AD7Engine.ContinueFromSynchronousEvent (the AD7ProgramCreateEvent path) dispatched ResumeFromLaunch through the blocking WorkerThread.RunOperation, coupling the VS UI/SDM thread to debugger I/O. Over a slow or remote (SSH) transport, AD7Engine.ContinueFromSynchronousEvent + ResumeFromLaunch could stall for a long time or indefinitely, producing a Watson hang. - Add WorkerThread.PostAsyncOperation, a non-blocking dispatch that claims the running-op slot (so later AD7 operations still serialize behind it) but returns without waiting for completion. Faults from the operation are routed to an onError callback from both the synchronous and async completion paths. - ContinueFromSynchronousEvent now posts ResumeFromLaunch via PostAsyncOperation and returns S_OK immediately, so the UI thread is no longer blocked. Resume faults report through SendStartDebuggingError + Terminate via onError, and synchronous failures (OnLoadComplete or the dispatch itself) are still handled locally, since the SDM drops errors returned from this method. - [x] Built and tested locally - [x] Debugged through WSL Linux gdb and the async resume completed.
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Address PR review: document that the ErrorHandler for an async operation may be invoked on a non-worker (task completion) thread, and invoke it while the running-op slot is still held so it does not run concurrently with the next queued operation. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 0b5e2926-4bce-44b8-bfab-8b9b7f36a615
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WardenGnaw
marked this pull request as ready for review
July 15, 2026 00:00
gregg-miskelly
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Looks good aside from the one suggestion
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gregg-miskelly
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Aside from Close, LGTM
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Had to also fix thie issue with Background actions are getting stuck waiting in the queue and may never running because thread went back to sleep. |
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@microsoft-github-policy-service rerun |
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AD7Engine.ContinueFromSynchronousEvent (the AD7ProgramCreateEvent path) dispatched ResumeFromLaunch through the blocking WorkerThread.RunOperation, coupling the VS UI/SDM thread to debugger I/O. Over a slow or remote (SSH) transport, AD7Engine.ContinueFromSynchronousEvent + ResumeFromLaunch could stall for a long time or indefinitely, producing a Watson hang.
Add WorkerThread.PostAsyncOperation, a non-blocking dispatch that claims the running-op slot (so later AD7 operations still serialize behind it) but returns without waiting for completion. Faults from the operation are routed to an onError callback from both the synchronous and async completion paths.
ContinueFromSynchronousEvent now posts ResumeFromLaunch via PostAsyncOperation and returns S_OK immediately, so the UI thread is no longer blocked. Resume faults report through SendStartDebuggingError + Terminate via onError, and synchronous failures (OnLoadComplete or the dispatch itself) are still handled locally, since the SDM drops errors returned from this method.
Built and tested locally