Move the cache for the marshaler methods to be stored on the RuntimeType instead of in a ConditionalWeakTable by jkoritzinsky · Pull Request #126621 · dotnet/runtime

jkoritzinsky · 2026-04-07T23:32:12Z

Move the marshalling info to be cached on the type itself instead of in a ConditionalWeakTable.

Move some of the validation (in particular the "has layout" validation) to be done only at "create" time so we don't have to rerun it for every time someone calls the Marshal methods with the same (valid) type.

Use the blittable fallbacks on StructureMarshaler<T> and LayoutClassMarshaler<T> instead of inlining the calls. The cost may go up slightly (delegate call to a method that calls SpanHelpers.Memmove instead of direct call to SpanHelpers.Memmove) but still much faster than the existing implementation that does the "is blittable" checks each time.

…ype instead of in a ConditionalWeakTable Should fix dotnet#126608

jkoritzinsky · 2026-04-07T23:32:46Z

@MihuBot benchmark Interop.StructureToPtr

dotnet-policy-service · 2026-04-07T23:33:33Z

Tagging subscribers to this area: @dotnet/area-system-reflection
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Copilot

Pull request overview

This PR moves the cache for Marshal.LayoutTypeMarshalerMethods from a ConditionalWeakTable<Type, …> to the per-RuntimeType generic cache infrastructure to address the reported interop performance regressions (issue #126608).

Changes:

Adds LayoutTypeMarshalerMethods storage to RuntimeType.CompositeCacheEntry so it can live in the existing RuntimeType generic cache.
Refactors LayoutTypeMarshalerMethods to implement RuntimeType.IGenericCacheEntry<T> and retrieves it via RuntimeType.GetOrCreateCacheEntry<T>().
Switches from delegate creation (CreateDelegate) to caching raw function pointers (MethodHandle.GetFunctionPointer) for the marshaler methods.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
`src/coreclr/System.Private.CoreLib/src/System/RuntimeType.GenericCache.cs`	Adds a new composite-cache field to hold the marshaler-methods cache on `RuntimeType`.
`src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs`	Reworks `LayoutTypeMarshalerMethods` to use `RuntimeType` cache entries and cached function pointers instead of a `ConditionalWeakTable`.

src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs

MihuBot · 2026-04-07T23:51:28Z

Interop.StructureToPtr

BenchmarkDotNet v0.16.0-nightly.20260320.467, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
AMD EPYC 9V74 2.60GHz, 1 CPU, 8 logical and 4 physical cores
Memory: 31.34 GB Total, 2.07 GB Available
  Job-TPEJOW : .NET 11.0.0 (11.0.0-dev, 42.42.42.42424), X64 RyuJIT x86-64-v4
  Job-HKHXHK : .NET 11.0.0 (11.0.0-dev, 42.42.42.42424), X64 RyuJIT x86-64-v4
EvaluateOverhead=False  OutlierMode=Default  PowerPlanMode=
IterationTime=250ms  MaxIterationCount=20  MemoryRandomization=Default
MinIterationCount=15  WarmupCount=1

Method	Toolchain	Mean	Error	Ratio	Allocated	Alloc Ratio
MarshalStructureToPtr	Main	53.46 ns	0.045 ns	1.00	24 B	1.00
MarshalStructureToPtr	PR	41.83 ns	0.073 ns	0.78	24 B	1.00

MarshalPtrToStructure	Main	57.27 ns	0.111 ns	1.00	24 B	1.00
MarshalPtrToStructure	PR	43.72 ns	0.169 ns	0.76	24 B	1.00

MarshalDestroyStructure	Main	109.19 ns	0.141 ns	1.00	96 B	1.00
MarshalDestroyStructure	PR	87.02 ns	0.241 ns	0.80	96 B	1.00

…ayout info for the type.

jkoritzinsky · 2026-04-08T18:00:31Z

@MihuBot benchmark Interop.StructureToPtr

MihuBot · 2026-04-08T18:17:49Z

Interop.StructureToPtr

BenchmarkDotNet v0.16.0-nightly.20260320.467, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
AMD EPYC 9V74 2.60GHz, 1 CPU, 8 logical and 4 physical cores
Memory: 31.34 GB Total, 1.78 GB Available
  Job-TPEJOW : .NET 11.0.0 (11.0.0-dev, 42.42.42.42424), X64 RyuJIT x86-64-v4
  Job-HKHXHK : .NET 11.0.0 (11.0.0-dev, 42.42.42.42424), X64 RyuJIT x86-64-v4
EvaluateOverhead=False  OutlierMode=Default  PowerPlanMode=
IterationTime=250ms  MaxIterationCount=20  MemoryRandomization=Default
MinIterationCount=15  WarmupCount=1

Method	Toolchain	Mean	Error	Ratio	Allocated	Alloc Ratio
MarshalStructureToPtr	Main	64.20 ns	0.578 ns	1.00	24 B	1.00
MarshalStructureToPtr	PR	30.70 ns	0.567 ns	0.48	24 B	1.00

MarshalPtrToStructure	Main	62.55 ns	0.117 ns	1.00	24 B	1.00
MarshalPtrToStructure	PR	37.14 ns	0.026 ns	0.59	24 B	1.00

MarshalDestroyStructure	Main	109.97 ns	0.152 ns	1.00	96 B	1.00
MarshalDestroyStructure	PR	68.63 ns	0.158 ns	0.62	96 B	1.00

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

Copilot · 2026-04-08T18:25:41Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs

            [RequiresDynamicCode("Marshalling code for the object might not be available.")]
-            internal static LayoutTypeMarshalerMethods GetMarshalMethodsForType(Type t)
+            public static LayoutTypeMarshalerMethods Create(RuntimeType type)
            {
-                return s_marshalerCache.GetOrAdd(t, CreateMarshalMethods);
+                if (!HasLayout(new QCallTypeHandle(ref type), out _, out int size))
+                    throw new ArgumentException(SR.Argument_MustHaveLayoutOrBeBlittable, nameof(type));

-                static LayoutTypeMarshalerMethods CreateMarshalMethods(Type type)
-                {
-                    Type instantiatedMarshaler = typeof(BoxedLayoutTypeMarshaler<>).MakeGenericType([type]);
-                    return new LayoutTypeMarshalerMethods(instantiatedMarshaler);
-                }
+                Type instantiatedMarshaler = typeof(BoxedLayoutTypeMarshaler<>).MakeGenericType([type]);
+                return new LayoutTypeMarshalerMethods(instantiatedMarshaler, size);
+            }


LayoutTypeMarshalerMethods.Create now throws ArgumentException(..., nameof(type)) when HasLayout is false. This exception can bubble out of public APIs like StructureToPtr / DestroyStructure, changing the observable ParamName from the prior values (structure / structuretype). Consider catching and rethrowing with the original parameter name at the public entrypoints (or in GetMarshalMethodsForType) so API behavior stays consistent, while keeping the per-type cache creation.

Copilot · 2026-04-08T18:25:42Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs

        public static unsafe void StructureToPtr(object structure, IntPtr ptr, bool fDeleteOld)
        {
            ArgumentNullException.ThrowIfNull(ptr);
            ArgumentNullException.ThrowIfNull(structure);

            RuntimeType type = (RuntimeType)structure.GetType();

            if (type.IsGenericType)
                throw new ArgumentException(SR.Argument_NeedNonGenericObject, nameof(structure));

-            if (!HasLayout(new QCallTypeHandle(ref type), out bool isBlittable, out int size))
-                throw new ArgumentException(SR.Argument_MustHaveLayoutOrBeBlittable, nameof(structure));
-
-            if (isBlittable)
-            {
-                SpanHelpers.Memmove(ref *(byte*)ptr, ref structure.GetRawData(), (nuint)size);
-                return;
-            }
-
            LayoutTypeMarshalerMethods methods = LayoutTypeMarshalerMethods.GetMarshalMethodsForType(type);

            if (fDeleteOld)
            {
-                methods.Free(structure, (byte*)ptr, size, ref Unsafe.NullRef<CleanupWorkListElement?>());
+                methods.Free((byte*)ptr);
            }

-            methods.ConvertToUnmanaged(structure, (byte*)ptr, size, ref Unsafe.NullRef<CleanupWorkListElement?>());
+            methods.ConvertToUnmanaged(structure, (byte*)ptr, ref Unsafe.NullRef<CleanupWorkListElement?>());
        }


The previous fast-path for blittable layout types (calling HasLayout(..., out isBlittable, out size) and doing a direct SpanHelpers.Memmove) was removed. The new path always routes through LayoutTypeMarshalerMethods / BoxedLayoutTypeMarshaler, which (for blittable structs/classes) performs extra delegate dispatch and also zeros the destination buffer (NativeMemory.Clear) before copying. This is a measurable perf/behavior change for the blittable case; if the intent of this PR is to address perf regressions, consider reintroducing a blittable fast-path (potentially using cached isBlittable + nativeSize in the RuntimeType cache entry) so blittable types remain a simple memmove without clearing.

Copilot · 2026-04-08T18:25:42Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs

        public static unsafe void DestroyStructure(IntPtr ptr, Type structuretype)
        {
            ArgumentNullException.ThrowIfNull(ptr);
            ArgumentNullException.ThrowIfNull(structuretype);

            if (structuretype is not RuntimeType rt)
                throw new ArgumentException(SR.Argument_MustBeRuntimeType, nameof(structuretype));

            if (rt.IsGenericType)
                throw new ArgumentException(SR.Argument_NeedNonGenericType, nameof(structuretype));

-            if (!HasLayout(new QCallTypeHandle(ref rt), out bool isBlittable, out int size))
-                throw new ArgumentException(SR.Argument_MustHaveLayoutOrBeBlittable, nameof(structuretype));
+            LayoutTypeMarshalerMethods methods = LayoutTypeMarshalerMethods.GetMarshalMethodsForType(rt);

-            if (!isBlittable)
-            {
-                LayoutTypeMarshalerMethods methods = LayoutTypeMarshalerMethods.GetMarshalMethodsForType(structuretype);
-
-                methods.Free(null, (byte*)ptr, size, ref Unsafe.NullRef<CleanupWorkListElement?>());
-            }
+            methods.Free((byte*)ptr);
        }


DestroyStructure previously did nothing for blittable types; it now always calls methods.Free((byte*)ptr). For blittable structs, StructureMarshaler<T>.Free clears the native memory (NativeMemory.Clear), which is a behavioral change and adds work on a hot path. Consider preserving the old semantics by skipping Free entirely for blittable types (again, this could be driven off cached isBlittable in the per-RuntimeType cache entry).

Copilot · 2026-04-08T18:25:42Z

src/coreclr/System.Private.CoreLib/src/System/StubHelpers.cs

        internal static unsafe void LayoutTypeConvertToUnmanaged(object obj, byte* pNative, ref CleanupWorkListElement? pCleanupWorkList)
        {
            RuntimeType type = (RuntimeType)obj.GetType();
-            bool hasLayout = Marshal.HasLayout(new QCallTypeHandle(ref type), out bool isBlittable, out int size);
-            Debug.Assert(hasLayout);
-
-            if (isBlittable)
-            {
-                SpanHelpers.Memmove(ref *pNative, ref obj.GetRawData(), (nuint)size);
-                return;
-            }
-
            Marshal.LayoutTypeMarshalerMethods methods = Marshal.LayoutTypeMarshalerMethods.GetMarshalMethodsForType(type);

-            methods.ConvertToUnmanaged(obj, pNative, size, ref pCleanupWorkList);
+            methods.ConvertToUnmanaged(obj, pNative, ref pCleanupWorkList);
        }


The previous blittable fast-path was removed here as well. LayoutTypeConvertToUnmanaged now always goes through Marshal.LayoutTypeMarshalerMethods, which for blittable types introduces extra indirection and (via StructureMarshaler / LayoutClassMarshaler) may clear the native buffer before copying. If these helpers are used on interop hot paths, consider restoring a blittable memmove fast-path using cached layout info to avoid the extra work.

Copilot · 2026-04-08T18:25:43Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs

+            internal static LayoutTypeMarshalerMethods GetMarshalMethodsForType(RuntimeType t)
+            {
+                return t.GetOrCreateCacheEntry<LayoutTypeMarshalerMethods>();
+            }


LayoutTypeMarshalerMethods.GetMarshalMethodsForType(RuntimeType) is no longer annotated with [RequiresDynamicCode], even though it can trigger MakeGenericType / delegate creation via the cache entry’s Create method. Previously the "get" helper carried the annotation, which helps flow the requirement to internal callers (e.g., StubHelpers.LayoutTypeConvertTo*). Consider restoring [RequiresDynamicCode] on GetMarshalMethodsForType (or otherwise ensuring the requirement is correctly surfaced) so trimming/AOT analysis remains accurate.

Move the cache for the marshaler methods to be stored on the RuntimeT…

20eb643

…ype instead of in a ConditionalWeakTable Should fix dotnet#126608

Copilot AI review requested due to automatic review settings April 7, 2026 23:32

github-actions bot added the area-System.Reflection label Apr 7, 2026

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[Benchmark X64] [jkoritzinsky] Move the cache for the marshaler methods to b ... MihuBot/runtime-utils#1843

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src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs Outdated Show resolved Hide resolved

jkoritzinsky added 2 commits April 8, 2026 10:52

Only validate that the type has layout the first time we set up the l…

8cc2f74

…ayout info for the type.

Keep the delegates (less need for unsafe)

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MihuBot mentioned this pull request Apr 8, 2026

[Benchmark X64] [jkoritzinsky] Move the cache for the marshaler methods to b ... MihuBot/runtime-utils#1844

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Move the cache for the marshaler methods to be stored on the RuntimeType instead of in a ConditionalWeakTable#126621

Move the cache for the marshaler methods to be stored on the RuntimeType instead of in a ConditionalWeakTable#126621
jkoritzinsky wants to merge 3 commits intodotnet:mainfrom
jkoritzinsky:marshal-regression-fix

jkoritzinsky commented Apr 7, 2026 •

edited

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jkoritzinsky commented Apr 7, 2026 •

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