[RuntimeAsync] Do not hold to the last used Continuation in the runtime async tasks. #121460
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VSadov
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Nov 8, 2025
This was referenced Nov 8, 2025
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jakobbotsch
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Nov 8, 2025
This reverts commit cc58bb0.
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Pull Request Overview
This PR refactors the continuation state management in async task operations to use move semantics, improving code clarity and adding defensive checks.
- Renames
GetContinuationStatetoMoveContinuationStateto reflect that the method now transfers ownership - Implements move semantics by clearing
m_stateObjectafter retrieval - Adds
Debug.Assertchecks to verifym_stateObjectis null before setting new values
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Fixes: #121459
The wrapped continuation is expected to be used only once - when the corresponding async method is resumed. We can and should null-out the continuation while fetching it in the dispatcher. There is no need to keep it referenced from the task once fetched as it may cause "leaks" observable via WeakReference/Finalization and the like.
The close analog of this behavior in the async1 is the C# state machine zeroing out pointer-containing fields in the display struct upon completing or faulting the task.
https://github.com/dotnet/roslyn/blob/f2df0ad6d3ef30ed033a794e7150a5600be50a95/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncMethodToStateMachineRewriter.cs#L186
https://github.com/dotnet/roslyn/blob/f2df0ad6d3ef30ed033a794e7150a5600be50a95/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncMethodToStateMachineRewriter.cs#L224