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Add AggressiveInlining to EnsureInitializedCore method to allow delegates stack alloc #122983

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Add AggressiveInlining to EnsureInitializedCore method to allow delegates stack alloc #122983

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Add AggressiveInlining to EnsureInitializedCore method to allow deleg…
SergeyTeplyakov Jan 7, 2026
2e72466
Merge branch 'main' into patch-1
SergeyTeplyakov Jan 7, 2026
5d8df04
Refactor EnsureInitializedCore to use Throw method
SergeyTeplyakov Jan 8, 2026
316d253
Update src/libraries/System.Private.CoreLib/src/System/Threading/Lazy…
SergeyTeplyakov Jan 8, 2026
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2 changes: 2 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System/Threading/LazyInitializer.cs
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Expand Up @@ -9,6 +9,7 @@

using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;

namespace System.Threading
{
Expand Down Expand Up @@ -109,6 +110,7 @@ public static T EnsureInitialized<T>([NotNull] ref T? target, Func<T> valueFacto
/// <param name="target">The variable that need to be initialized</param>
/// <param name="valueFactory">The delegate that will be executed to initialize the target</param>
/// <returns>The initialized variable</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static T EnsureInitializedCore<T>([NotNull] ref T? target, Func<T> valueFactory) where T : class
{
T value = valueFactory() ?? throw new InvalidOperationException(SR.Lazy_StaticInit_InvalidOperation);
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@EgorBo EgorBo Jan 7, 2026

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Moving throw new InvalidOperationException(SR.Lazy_StaticInit_InvalidOperation); to a throw-helper should also work, probably it's a better approach

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@SergeyTeplyakov SergeyTeplyakov Jan 7, 2026

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I've tried just moving it to a helper without AggressiveInlining, but it was not enough. The AggressiveInlining was still required in this case. And because of that, I've decided not to move the 'throw' into a helper.

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@EgorBo EgorBo Jan 7, 2026

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hm.. then it's fine as is, but the inliner needs some tuning apparently

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@EgorBo EgorBo Jan 7, 2026 •
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There are more EnsureInitializedCore overloads in this file, any reason why only this one needs AggressiveInlining?

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@SergeyTeplyakov SergeyTeplyakov Jan 7, 2026

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There are 2 more overloads that takes Func:

public static T EnsureInitialized<T>([NotNull] ref T? target, [NotNullIfNotNull(nameof(syncLock))] ref object? syncLock, Func<T> valueFactory) where T : class;

public static T EnsureInitialized<T>([AllowNull] ref T target, ref bool initialized, [NotNullIfNotNull(nameof(syncLock))] ref object? syncLock, Func<T> valueFactory);

I've tried adding AggressiveInlining to both of them (to EnsureInitializedCore methods), and here are the results:

| Method                                     | Runtime   | Mean      | Allocated |
|------------------------------------------- |---------- |----------:|----------:|
| EnsureInitialized_Old                      | .NET 10.0 |  5.873 ns |      88 B |
| EnsureInitialized_New                      | .NET 10.0 |  1.744 ns |      24 B |
| EnsureInitialized_SyncRoot_Old             | .NET 10.0 |  5.729 ns |      88 B |
| EnsureInitialized_SyncRoot_New             | .NET 10.0 |  5.692 ns |      88 B |
| EnsureInitialized_Initialized_SyncRoot_Old | .NET 10.0 | 18.475 ns |      24 B |
| EnsureInitialized_Initialized_SyncRoot_New | .NET 10.0 | 18.614 ns |      24 B |
| EnsureInitialized_Old                      | .NET 9.0  |  6.522 ns |      88 B |
| EnsureInitialized_New                      | .NET 9.0  |  6.561 ns |      88 B |
| EnsureInitialized_SyncRoot_Old             | .NET 9.0  |  6.566 ns |      88 B |
| EnsureInitialized_SyncRoot_New             | .NET 9.0  |  6.485 ns |      88 B |
| EnsureInitialized_Initialized_SyncRoot_Old | .NET 9.0  | 22.287 ns |      88 B |
| EnsureInitialized_Initialized_SyncRoot_New | .NET 9.0  | 19.889 ns |      88 B |

So in both cases the AggressiveInlining has no effect. For the first case, the JIT can't inline the method even with AggressiveInlining attribute so we still have 88B of allocations (for both the delegate and the closure), and for the second overload the JIT can inline the old version, so in both cases we have only the delegate allocation.

So I can add the attribute for consistency, but it seems that it has no effect currently for other 2 cases.

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@stephentoub stephentoub Jan 8, 2026

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Can you share what specifically you tried with regards to outlining the throw? With that this attr really shouldn't be necessary, and if it is, that suggests a broader inlining issue we should fix instead.

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@SergeyTeplyakov SergeyTeplyakov Jan 8, 2026

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Pushed another commit with the proposed change and trigerred the EgorBot to see the before and after results.
Running this version locally was not enough to make the Core method inlined by the JIT.

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