Fix headless session hang when cleanup throws - #21781
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MrJul merged 3 commits intoJul 20, 2026
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A dispatcher job that throws during work-item cleanup leaves the dispatch task incomplete and prevents later work from running. The session contract requires every queued dispatch to reach a terminal state. Add behavioral coverage that posts a throwing cleanup job, expects its exception from Dispatch, and verifies the assembly session can process the next dispatch. The shared NUnit test runs under both PerTest and PerAssembly projects.
An exception during application cleanup escapes the work item before its completion source is settled, faults the private consumer task, and leaves current and future Dispatch calls waiting forever. Capture cleanup failures as the work item's exception so the consumer can continue. Restore synchronization context, locator scope, and dispatcher state in finally blocks before processing later work.
NathanDrake2406
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maxkatz6
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MrJul
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* test(headless): reproduce cleanup exception dispatch hang A dispatcher job that throws during work-item cleanup leaves the dispatch task incomplete and prevents later work from running. The session contract requires every queued dispatch to reach a terminal state. Add behavioral coverage that posts a throwing cleanup job, expects its exception from Dispatch, and verifies the assembly session can process the next dispatch. The shared NUnit test runs under both PerTest and PerAssembly projects. * fix(headless): report dispatch cleanup exceptions An exception during application cleanup escapes the work item before its completion source is settled, faults the private consumer task, and leaves current and future Dispatch calls waiting forever. Capture cleanup failures as the work item's exception so the consumer can continue. Restore synchronization context, locator scope, and dispatcher state in finally blocks before processing later work. --------- Co-authored-by: Julien Lebosquain <julien@lebosquain.net>
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What does the pull request do?
Fixes a deterministic
HeadlessUnitTestSessionhang when a dispatcher job throws during work-item cleanup. The cleanup exception is now reported through the affectedDispatchtask, and the session remains able to process later work.This is the cleanup-stage counterpart to the application-construction fix in #21688.
What is the current behavior?
Cleanup runs before a dispatch's
TaskCompletionSourceis settled, as required by #21223. Ifapplication.Dispose()throws, the exception bypasses the completion code and escapes the queued action. The private consumer task faults, the currentDispatchtask never completes, and all later dispatches remain queued forever.What is the updated/expected behavior with this PR?
The affected
Dispatchtask faults with the cleanup exception. Required synchronization context, locator scope, and dispatcher state restoration still runs, so the consumer remains healthy and a subsequent dispatch completes normally.The regression test posts a dispatcher job that throws during cleanup, verifies the exact
InvalidOperationExceptionis surfaced, then verifies another dispatch returns successfully. It runs in both NUnit isolation projects.Validation on macOS ARM64 with .NET 10:
How was the solution implemented (if it's not obvious)?
DispatchCorecatches exceptions from application disposal and stores them as the work item's result before completing itsTaskCompletionSource. Cleanup callbacks usefinallyblocks to restore ambient state even when a dispatcher cleanup job throws.The commits follow the repository's bug-fix convention: the first commit adds the failing behavioral test, and the second commit contains the fix.
Checklist
Breaking changes
None. The failure path now completes with the original cleanup exception instead of hanging indefinitely.
Obsoletions / Deprecations
None.
Fixed issues
Fixes #21770