[Async v2] Implement async method variant handling in AddMethod and UpdateMethod by tommcdon · Pull Request #125397 · dotnet/runtime

tommcdon · 2026-03-10T18:33:59Z

This change implements a TODO item in EEClass::AddMethodDesc to support Runtime Async

dotnet-policy-service · 2026-03-10T18:35:00Z

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Copilot

Pull request overview

This PR implements runtime-async method variant support in the Edit-and-Continue (EnC) path by extending EEClass::AddMethodDesc/EEClass::AddMethod to carry async metadata (flags + optional alternate signature) and by updating EnC method update logic to consider async method variants.

Changes:

Extend EEClass::AddMethodDesc to accept async flags and an optional async-variant signature, and plumb that into MethodTableBuilder::InitMethodDesc.
Add async return-type classification and async-variant creation logic to EEClass::AddMethod.
Update EditAndContinueModule::UpdateMethod to also reset the entrypoint for the method’s async counterpart.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/coreclr/vm/encee.cpp	Resets entrypoints for async counterparts during EnC method updates.
src/coreclr/vm/class.h	Extends `AddMethodDesc` signature to accept async flags and optional async signature.
src/coreclr/vm/class.cpp	Implements async return classification and passes async flags/signature into EnC-added `MethodDesc` creation.

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Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

…ejection, generic UpdateMethod comment - class.cpp:579: Update GC violation comment to acknowledge the extern-alias edge case as Won't Fix per reviewer feedback - class.cpp:597: Reject infrastructure async methods (IsMiAsync but not task-returning) on non-system modules with COR_E_BADIMAGEFORMAT, mirroring MethodTableBuilder validation - encee.cpp:388: Add comment explaining that ResetCodeEntryPointForEnC cascades from thunk to async variant automatically, so generic UpdateMethod path does not need explicit async variant handling Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

noahfalk

Looks good 👍 Couple suggestions inline

Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Use GetAsyncOtherVariantNoCreate in UpdateMethod

Extract BuildAsyncVariantSignature to share async signature construction The async variant signature construction logic (stripping Task/ValueTask wrapper from the return type) was duplicated between MethodTableBuilder (initial type load) and EEClass::AddMethod (EnC add method). Extract it into a shared BuildAsyncVariantSignature helper in method.cpp. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

When adding a new async method to a generic type via EnC, the async variant MethodDesc was only created for the type definition but not for existing canonical instantiations. This caused crashes when the newly added async method was called on value type instantiations (e.g. G<int>) because the thunk could not find its async variant. Hoist the async variant signature and flags computation above the generic instantiation loop, then create the async variant for each canonical MethodTable alongside the primary thunk. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ejection, generic UpdateMethod comment - class.cpp:579: Update GC violation comment to acknowledge the extern-alias edge case as Won't Fix per reviewer feedback - class.cpp:597: Reject infrastructure async methods (IsMiAsync but not task-returning) on non-system modules with COR_E_BADIMAGEFORMAT, mirroring MethodTableBuilder validation - encee.cpp:388: Add comment explaining that ResetCodeEntryPointForEnC cascades from thunk to async variant automatically, so generic UpdateMethod path does not need explicit async variant handling Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…VariantSignature Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ure async in EnC - Clarify GC violation comment to explain the specific unlikely scenario (naming collision + extern alias + hot reload while debugging) - Reject infrastructure async methods unconditionally in EnC rather than only on non-system modules, since no scenario benefits from allowing them Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…T_NOT_SUPPORTED - Rewrite GC violation comment per jkotas: the issue is unresolved TypeRef/AssemblyRef for Task/ValueTask, not type misidentification. System.Runtime is typically already resolved so this is unlikely. - Use CORDBG_E_ENC_EDIT_NOT_SUPPORTED instead of COR_E_BADIMAGEFORMAT for infrastructure async rejection, since this is an unsupported edit rather than malformed metadata. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Allocate the async variant signature from each instantiation's own LoaderAllocator instead of reusing the type definition's allocation. AddMethodDesc stores the signature as a raw pointer in AsyncMethodData, so it must be owned by the same allocator as the MethodDesc to avoid dangling pointers on collectible ALC unload. Also fix GC violation comment per jkotas feedback and use CORDBG_E_ENC_EDIT_NOT_SUPPORTED for infrastructure async rejection. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Generic instantiations are guaranteed to have same or shorter lifetime than the method definition, so reusing the type definition's signature allocation is safe. Remove the unnecessary per-allocator copy. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Previously, AddMethod eagerly created async variant MethodDescs for all runtime-async methods added via EnC (on the type-def and every existing generic instantiation). This commit defers variant creation to the point of first use: - FindOrCreateAssociatedMethodDesc (genmeth.cpp): lazily creates the variant using double-check locking with m_InstMethodHashTableCrst, matching the existing NewInstantiatedMethodDesc pattern. - LoadTypicalMethodDefinition (method.cpp): triggers lazy creation when navigating from an instantiation variant back to the type-def variant. - AddAsyncVariant (class.cpp): new helper that computes the variant signature on-demand from metadata (ClassifyMethodReturnKind + BuildAsyncVariantSignature) rather than storing it on primary thunks. - ResetCodeEntryPointForEnC (method.cpp): gracefully handles the case where the variant has not been created yet (no-op). - InitMethodDesc (methodtablebuilder.cpp): restored original contract where only IsAsyncVariant methods store a signature. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

AddChunk publishes a new MethodDescChunk to a lock-free linked list that concurrent readers iterate without holding a lock. On weakly ordered architectures (ARM64), plain stores can be reordered, allowing a reader to see the new chunk pointer before the chunk's internal data (MethodDescs, flags, etc.) is fully visible. Use VolatileStore at both publish points (head and tail) to act as a release barrier, matching the pattern used elsewhere in the VM (e.g. dacenumerablehash.inl, codeversion.cpp, eehash.inl). This is a no-op on x86/x64 (strong memory model). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Gate ClassifyMethodReturnKind on IsMiAsync in AddMethod so non-async methods never hit the GC-triggering type resolution path. Updated comment to note EnC runs with threads suspended. - Fix redundant double-reset in UpdateMethod: ResetCodeEntryPointForEnC already cascades from thunk to IL-owning variant, so skip the explicit variant reset when pMethod is the thunk. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…avoidance Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The explicit reset of the paired async variant in UpdateMethod is dead code: UpdateMethod always receives the thunk (from the delta metadata token), so !IsAsyncThunkMethod() is always false and the block never fires. Even if it did, ResetCodeEntryPointForEnC already cascades from the thunk to the IL-owning variant automatically. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Consolidate the IsMiAsync handling into a single block with early return for non-task-returning methods, removing the intermediate isAsyncTaskReturning variable and separate if/else-if chain. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- AddAsyncVariant: replace standalone assert with runtime guard that returns COR_E_BADIMAGEFORMAT for non-task-returning methods in Release builds (assert inside for Debug). - FCAMD: gate lazy async variant creation on IsAsyncThunkMethod() to prevent calling AddAsyncVariant on non-async EnC methods. - GetChunks/GetNextChunk: pair VolatileStore in AddChunk with VolatileLoad on readers for proper acquire/release semantics on weak memory models. DAC paths use plain loads. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Restore the comment explaining that ClassifyMethodReturnKind matching by type name without verifying the assembly reference is a legitimate but corner case bug (extern alias + naming collision + hot reload), accepted as Won't Fix rather than claiming GC is safe in practice. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Remove pMDescInCanonMT->GetMethodTable() != pExactMT->GetCanonicalMethodTable() condition (always false since GetParallelMethodDesc searches the canonical MT). Replace with asserts to verify the invariant. - Update GC safety comment to acknowledge the ClassifyMethodReturnKind extern alias corner case as a legitimate Won't Fix bug. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Update AsyncVariantLookup enum values: AsyncOtherVariant -> Async, MatchingAsyncVariant -> Ordinary - Update ClassifyMethodReturnKind calls to pass new elementTypeLength param - Update FindOrCreateAssociatedMethodDesc call to match new parameter order (AsyncVariantLookup moved before forceRemotableMethod) - Update debugger.cpp: HasAsyncOtherVariant -> IsAsyncThunkMethod, GetAsyncOtherVariantNoCreate -> GetAsyncVariantNoCreate - Add missing variable declarations in methodtablebuilder.cpp - Remove tautological assert in FCAMD lazy creation block Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…cation Reverts the unnecessary variable declaration reordering in EnumerateClassMethods that fell out of the rebase conflict resolution. Keeps the improved comment in InitMethodDesc that clarifies primary thunks use the original metadata signature and do not store one. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

tommcdon added this to the 11.0.0 milestone Mar 10, 2026

tommcdon self-assigned this Mar 10, 2026

tommcdon added the area-Diagnostics-coreclr label Mar 10, 2026

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tommcdon force-pushed the dev/tommcdon/implement_addmethoddesc branch from 76d4eb1 to 437f9ed Compare March 20, 2026 20:08

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tommcdon and others added 22 commits April 16, 2026 15:09

Implement async method variant handling in AddMethod and UpdateMethod

31d59eb

Use async variant in EditAndContinueModule::UpdateMethod

0e5fc4d

Use GetAsyncOtherVariantNoCreate in UpdateMethod

Remove dead store taskTokenOffsetFromAsyncDetailsOffset in BuildAsync…

e15eebd

…VariantSignature Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Replace Unicode arrows with ASCII in C++ comments

d587af7

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Fix misleading comment: classification is for async variants, not GC …

271c359

…avoidance Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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