perf: defer per-mock allocations in ChunkedSlotStorage and MockScenarioSetup

Benchmarks/Mockolate.Benchmarks/MockCreationBenchmarks.cs

@@ -0,0 +1,58 @@
+using BenchmarkDotNet.Attributes;
+using FakeItEasy;
+using Imposter.Abstractions;
+using Mockolate.Benchmarks;
+using NSubstitute;
+
+[assembly: GenerateImposter(typeof(MockCreationBenchmarks.ICalculatorService))]
+
+namespace Mockolate.Benchmarks;
+#pragma warning disable CA1822 // Mark members as static
+
+/// <summary>
+///     Measures the cost of creating an empty mock — no setup, no invocations, no verification.
+/// </summary>
+public class MockCreationBenchmarks : BenchmarksBase
+{
+	[Benchmark(Baseline = true, Description = "Mockolate")]
+	public object Mockolate_CreateMock()
+		=> ICalculatorService.CreateMock();
+
+	[Benchmark(Description = "Imposter")]
+	public object Imposter_CreateMock()
+	{
+		ICalculatorServiceImposter imposter = ICalculatorService.Imposter();
+		return imposter.Instance();
+	}
+
+	[Benchmark(Description = "TUnit.Mocks")]
+	public object TUnitMocks_CreateMock()
+	{
+		TUnit.Mocks.Mock<ICalculatorService> mock = TUnit.Mocks.Mock.Of<ICalculatorService>();
+		return mock.Object;
+	}
+
+	[Benchmark(Description = "Moq")]
+	public object Moq_CreateMock()
+	{
+		Moq.Mock<ICalculatorService> mock = new();
+		return mock.Object;
+	}
+
+	[Benchmark(Description = "NSubstitute")]
+	public object NSubstitute_CreateMock()
+		=> Substitute.For<ICalculatorService>();
+
+	[Benchmark(Description = "FakeItEasy")]
+	public object FakeItEasy_CreateMock()
+		=> A.Fake<ICalculatorService>();
+
+	public interface ICalculatorService
+	{
+		int Zero { get; }
+		int Add(int a, int b);
+		double Divide(double numerator, double denominator);
+		string Format(int value);
+	}
+}
+#pragma warning restore CA1822 // Mark members as static

Source/Mockolate/Interactions/ChunkedSlotStorage.cs

@@ -13,9 +13,10 @@ namespace Mockolate.Interactions;
 ///     Slot N is stored at <c>chunks[N &gt;&gt; <see cref="ChunkShift" />][N &amp; <see cref="ChunkMask" />]</c>.
 ///     A writer reserves a unique slot via <see cref="Reserve" />, obtains its destination via
 ///     <see cref="SlotForWrite" />, writes its fields, then calls <see cref="Publish" />.
-///     The chunks array itself doubles when a new chunk index is past its end; that grow only copies
-///     chunk references (which are stable once installed), so a concurrent writer to an existing
-///     chunk cannot lose its data.
+///     The chunks array itself is allocated lazily on the first <see cref="SlotForWrite" /> and
+///     doubles when a new chunk index is past its end; that grow only copies chunk references
+///     (which are stable once installed), so a concurrent writer to an existing chunk cannot lose
+///     its data. A buffer that is never written into stays allocation-free past its own header.
 /// </remarks>
 #if !DEBUG
 [System.Diagnostics.DebuggerNonUserCode]
@@ -27,8 +28,8 @@ internal sealed class ChunkedSlotStorage<TRecord> where TRecord : struct
 	internal const int ChunkMask = ChunkSize - 1;
 
 	internal readonly MockolateLock Lock = new();
-	internal TRecord[]?[] Chunks = new TRecord[1][];
-	internal bool[]?[] VerifiedChunks = new bool[1][];
+	internal TRecord[]?[]? Chunks;
+	internal bool[]?[]? VerifiedChunks;
 	private int _reserved;
 	private int _published;
 
@@ -52,8 +53,10 @@ public ref TRecord SlotForWrite(int slot)
 	{
 		int chunkIdx = slot >> ChunkShift;
 		int offset = slot & ChunkMask;
-		TRecord[]?[] chunks = Volatile.Read(ref Chunks);
-		TRecord[]? chunk = chunkIdx < chunks.Length ? Volatile.Read(ref chunks[chunkIdx]) : null;
+		TRecord[]?[]? chunks = Volatile.Read(ref Chunks);
+		TRecord[]? chunk = chunks is not null && chunkIdx < chunks.Length
+			? Volatile.Read(ref chunks[chunkIdx])
+			: null;
 		if (chunk is null)
 		{
 			chunk = EnsureChunk(chunkIdx);
@@ -71,7 +74,7 @@ public ref TRecord SlotUnderLock(int slot)
 	{
 		int chunkIdx = slot >> ChunkShift;
 		int offset = slot & ChunkMask;
-		return ref Chunks[chunkIdx]![offset];
+		return ref Chunks![chunkIdx]![offset];
 	}
 
 	/// <summary>
@@ -81,7 +84,7 @@ public ref bool VerifiedUnderLock(int slot)
 	{
 		int chunkIdx = slot >> ChunkShift;
 		int offset = slot & ChunkMask;
-		return ref VerifiedChunks[chunkIdx]![offset];
+		return ref VerifiedChunks![chunkIdx]![offset];
 	}
 
 	/// <summary>
@@ -92,14 +95,17 @@ public void Clear()
 		lock (Lock)
 		{
 			int n = _published;
-			TRecord[]?[] chunks = Chunks;
-			bool[]?[] verified = VerifiedChunks;
-			for (int slot = 0; slot < n; slot++)
+			if (n > 0)
 			{
-				int chunkIdx = slot >> ChunkShift;
-				int offset = slot & ChunkMask;
-				chunks[chunkIdx]![offset] = default;
-				verified[chunkIdx]![offset] = false;
+				TRecord[]?[] chunks = Chunks!;
+				bool[]?[] verified = VerifiedChunks!;
+				for (int slot = 0; slot < n; slot++)
+				{
+					int chunkIdx = slot >> ChunkShift;
+					int offset = slot & ChunkMask;
+					chunks[chunkIdx]![offset] = default;
+					verified[chunkIdx]![offset] = false;
+				}
 			}
 
 			_reserved = 0;
@@ -111,8 +117,20 @@ private TRecord[] EnsureChunk(int chunkIdx)
 	{
 		lock (Lock)
 		{
-			TRecord[]?[] chunks = Chunks;
-			if (chunkIdx >= chunks.Length)
+			TRecord[]?[]? chunks = Chunks;
+			if (chunks is null)
+			{
+				int initialLen = 1;
+				while (chunkIdx >= initialLen)
+				{
+					initialLen *= 2;
+				}
+
+				chunks = new TRecord[initialLen][];
+				VerifiedChunks = new bool[initialLen][];
+				Volatile.Write(ref Chunks, chunks);
+			}
+			else if (chunkIdx >= chunks.Length)
 			{
 				int newLen = chunks.Length;
 				while (chunkIdx >= newLen)
@@ -123,7 +141,7 @@ private TRecord[] EnsureChunk(int chunkIdx)
 				TRecord[]?[] biggerChunks = new TRecord[newLen][];
 				Array.Copy(chunks, biggerChunks, chunks.Length);
 				bool[]?[] biggerVerified = new bool[newLen][];
-				Array.Copy(VerifiedChunks, biggerVerified, VerifiedChunks.Length);
+				Array.Copy(VerifiedChunks!, biggerVerified, VerifiedChunks!.Length);
 				chunks = biggerChunks;
 				VerifiedChunks = biggerVerified;
 				Volatile.Write(ref Chunks, chunks);
@@ -133,7 +151,7 @@ private TRecord[] EnsureChunk(int chunkIdx)
 			if (chunk is null)
 			{
 				chunk = new TRecord[ChunkSize];
-				VerifiedChunks[chunkIdx] = new bool[ChunkSize];
+				VerifiedChunks![chunkIdx] = new bool[ChunkSize];
 				Volatile.Write(ref chunks[chunkIdx], chunk);
 			}
 

Source/Mockolate/Setup/MockSetups.cs

@@ -3,6 +3,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Text;
+using System.Threading;
 
 namespace Mockolate.Setup;
 
@@ -52,35 +53,87 @@ public bool TryGetScenario(string setupScenario, [NotNullWhen(true)] out MockSce
 
 internal class MockScenarioSetup
 {
-	internal MockSetups.EventSetups Events { get; } = new();
-	internal MockSetups.IndexerSetups Indexers { get; } = new();
-	internal MockSetups.MethodSetups Methods { get; } = new();
-	internal MockSetups.PropertySetups Properties { get; } = new();
+	private MockSetups.EventSetups? _events;
+	private MockSetups.IndexerSetups? _indexers;
+	private MockSetups.MethodSetups? _methods;
+	private MockSetups.PropertySetups? _properties;
+
+	internal MockSetups.EventSetups Events
+	{
+		get
+		{
+			if (_events is null)
+			{
+				Interlocked.CompareExchange(ref _events, new MockSetups.EventSetups(), null);
+			}
+
+			return _events!;
+		}
+	}
+
+	internal MockSetups.IndexerSetups Indexers
+	{
+		get
+		{
+			if (_indexers is null)
+			{
+				Interlocked.CompareExchange(ref _indexers, new MockSetups.IndexerSetups(), null);
+			}
+
+			return _indexers!;
+		}
+	}
+
+	internal MockSetups.MethodSetups Methods
+	{
+		get
+		{
+			if (_methods is null)
+			{
+				Interlocked.CompareExchange(ref _methods, new MockSetups.MethodSetups(), null);
+			}
+
+			return _methods!;
+		}
+	}
+
+	internal MockSetups.PropertySetups Properties
+	{
+		get
+		{
+			if (_properties is null)
+			{
+				Interlocked.CompareExchange(ref _properties, new MockSetups.PropertySetups(), null);
+			}
+
+			return _properties!;
+		}
+	}
 
 	/// <inheritdoc cref="object.ToString()" />
 	[EditorBrowsable(EditorBrowsableState.Never)]
 	public override string ToString()
 	{
 		StringBuilder sb = new();
-		int methodCount = Methods.Count;
+		int methodCount = _methods?.Count ?? 0;
 		if (methodCount > 0)
 		{
 			sb.Append(methodCount).Append(methodCount == 1 ? " method, " : " methods, ");
 		}
 
-		int propertyCount = Properties.Count;
+		int propertyCount = _properties?.Count ?? 0;
 		if (propertyCount > 0)
 		{
 			sb.Append(propertyCount).Append(propertyCount == 1 ? " property, " : " properties, ");
 		}
 
-		int indexerCount = Indexers.Count;
+		int indexerCount = _indexers?.Count ?? 0;
 		if (indexerCount > 0)
 		{
 			sb.Append(indexerCount).Append(indexerCount == 1 ? " indexer, " : " indexers, ");
 		}
 
-		int eventCount = Events.Count;
+		int eventCount = _events?.Count ?? 0;
 		if (eventCount > 0)
 		{
 			sb.Append(eventCount).Append(eventCount == 1 ? " event, " : " events, ");