perf: defer eager allocations in the mock-creation path

Source/Mockolate.SourceGenerators/Sources/Sources.MockClass.cs

@@ -934,7 +934,7 @@ public static string MockClass(
 		else
 		{
 			sb.Append("\t\t\tmockBehavior ??= global::Mockolate.MockBehavior.Default;").AppendLine();
-			sb.Append("\t\t\tglobal::Mockolate.MockRegistry mockRegistry = new global::Mockolate.MockRegistry(mockBehavior, global::Mockolate.Mock.").Append(name).Append(".CreateFastInteractions(mockBehavior), constructorParameters);").AppendLine();
+			sb.Append("\t\t\tglobal::Mockolate.MockRegistry mockRegistry = new global::Mockolate.MockRegistry(mockBehavior, global::Mockolate.Mock.").Append(name).Append(".MemberCount, constructorParameters);").AppendLine();
 		}
 
 		sb.Append("\t\t\treturn CreateMockInstance(mockRegistry, constructorParameters, setup);").AppendLine();
@@ -1383,7 +1383,7 @@ private static void AppendCreateRegistryFromBehavior(StringBuilder sb, string in
 		sb.Append(indent).Append("/// </summary>").AppendLine();
 		sb.Append(indent).Append("private static global::Mockolate.MockRegistry MockolateCreateRegistryFromBehavior(global::Mockolate.MockBehavior behavior)").AppendLine();
 		sb.Append(indent).Append("{").AppendLine();
-		sb.Append(indent).Append("\tglobal::Mockolate.MockRegistry registry = new global::Mockolate.MockRegistry(behavior, CreateFastInteractions(behavior));").AppendLine();
+		sb.Append(indent).Append("\tglobal::Mockolate.MockRegistry registry = new global::Mockolate.MockRegistry(behavior, MemberCount);").AppendLine();
 		if (setsMockRegistryProvider)
 		{
 			sb.Append(indent).Append("\tMockRegistryProvider.Value = registry;").AppendLine();

Source/Mockolate/Interactions/FastMockInteractions.cs

@@ -22,7 +22,20 @@ public class FastMockInteractions : IMockInteractions
 	private long _globalSequence;
 
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
-	private readonly MockolateLock _verifiedLock = new();
+	[field: DebuggerBrowsable(DebuggerBrowsableState.Never)]
+	private MockolateLock VerifiedLock
+	{
+		get
+		{
+			if (field is { } existing)
+			{
+				return existing;
+			}
+
+			Interlocked.CompareExchange(ref field, new MockolateLock(), null);
+			return field!;
+		}
+	}
 
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
 	private HashSet<IInteraction>? _verified;
@@ -191,7 +204,7 @@ public IReadOnlyCollection<IInteraction> GetUnverifiedInteractions()
 			unverified.Sort(static (left, right) => left.Seq.CompareTo(right.Seq));
 		}
 
-		lock (_verifiedLock)
+		lock (VerifiedLock)
 		{
 			if (_verified is null || _verified.Count == 0)
 			{
@@ -224,7 +237,7 @@ public IReadOnlyCollection<IInteraction> GetUnverifiedInteractions()
 
 	void IMockInteractions.Verified(IEnumerable<IInteraction> interactions)
 	{
-		lock (_verifiedLock)
+		lock (VerifiedLock)
 		{
 			_verified ??= [];
 			foreach (IInteraction interaction in interactions)
@@ -245,7 +258,7 @@ public void Clear()
 
 		Volatile.Read(ref _fallback)?.Clear();
 
-		lock (_verifiedLock)
+		lock (VerifiedLock)
 		{
 			_verified = null;
 		}

Source/Mockolate/MockRegistry.Interactions.cs

@@ -11,10 +11,20 @@ namespace Mockolate;
 
 public partial class MockRegistry
 {
+	private IMockInteractions? _interactions;
+	private readonly int _interactionMemberCount;
+
 	/// <summary>
 	///     Gets the collection of interactions recorded by the mock object.
 	/// </summary>
-	public IMockInteractions Interactions { get; }
+	public IMockInteractions Interactions => _interactions ?? EnsureInteractions();
+
+	private IMockInteractions EnsureInteractions()
+	{
+		Interlocked.CompareExchange(ref _interactions,
+			new FastMockInteractions(_interactionMemberCount, Behavior.SkipInteractionRecording), null);
+		return _interactions!;
+	}
 
 	/// <summary>
 	///     Clears all interactions recorded by the mock object.
@@ -131,16 +141,17 @@ public void ClearAllInteractions()
 	/// <returns>A lazy stream of matching setups, scenario-scoped first.</returns>
 	public IEnumerable<T> GetMethodSetups<T>(string methodName) where T : MethodSetup
 	{
-		if (!string.IsNullOrEmpty(Scenario) &&
-		    Setup.TryGetScenario(Scenario, out MockScenarioSetup? scopedBucket))
+		MockSetups? setups = _setups;
+		if (!string.IsNullOrEmpty(Scenario) && setups is not null &&
+		    setups.TryGetScenario(Scenario, out MockScenarioSetup? scopedBucket))
 		{
 			return EnumerateScopedAndGlobalMethodSetups<T>(methodName, scopedBucket);
 		}
 
 		MethodSetup[]?[]? snapshot = Volatile.Read(ref _setupsByMemberId);
 		if (snapshot is null)
 		{
-			return Setup.Methods.EnumerateByName<T>(methodName);
+			return setups is null ? Array.Empty<T>() : setups.Methods.EnumerateByName<T>(methodName);
 		}
 
 		return EnumerateGlobalMethodSetups<T>(methodName, snapshot);
@@ -178,11 +189,14 @@ private IEnumerable<T> EnumerateGlobalMethodSetups<T>(string methodName,
 		}
 
 		// Hand-written SetupMethod(MethodSetup) entries (e.g. the HttpClientExtensions pipeline) live
-		// only in the root dict; the empty-storage fast path returns Array.Empty<T> so the loop
-		// allocates nothing further when no such entry exists.
-		foreach (T setup in Setup.Methods.EnumerateByName<T>(methodName))
+		// only in the root dict; when no MockSetups has been allocated there can be none, so the loop
+		// is skipped entirely and never forces the lazy allocation.
+		if (_setups is { } setups)
 		{
-			yield return setup;
+			foreach (T setup in setups.Methods.EnumerateByName<T>(methodName))
+			{
+				yield return setup;
+			}
 		}
 	}
 

Source/Mockolate/MockRegistry.Setup.cs

@@ -9,15 +9,28 @@ namespace Mockolate;
 public partial class MockRegistry
 {
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
-	private readonly object _setupsByMemberIdLock = new();
+	[field: DebuggerBrowsable(DebuggerBrowsableState.Never)]
+	private object SetupsByMemberIdLock
+	{
+		get
+		{
+			if (field is { } existing)
+			{
+				return existing;
+			}
+
+			Interlocked.CompareExchange(ref field, new object(), null);
+			return field!;
+		}
+	}
 
 	/// <summary>
 	///     Returns the generator-known member count hint when <see cref="Interactions" /> is a
 	///     <see cref="FastMockInteractions" />, so dispatch tables can be sized once on first allocation
 	///     instead of growing one slot at a time as setups for higher-numbered members come in.
 	/// </summary>
 	private int GetMemberCountHint()
-		=> Interactions is FastMockInteractions fast ? fast.Buffers.Length : 0;
+		=> _interactions is FastMockInteractions fast ? fast.Buffers.Length : _interactionMemberCount;
 
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
 	private EventSetup[]?[]? _eventSetupsByMemberId;
@@ -31,10 +44,19 @@ private int GetMemberCountHint()
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
 	private MethodSetup[]?[]? _setupsByMemberId;
 
+	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
+	private MockSetups? _setups;
+
 	/// <summary>
 	///     The registered setups for the mock, including methods, properties, indexers and events.
 	/// </summary>
-	internal MockSetups Setup { get; }
+	internal MockSetups Setup => _setups ?? EnsureSetups();
+
+	private MockSetups EnsureSetups()
+	{
+		Interlocked.CompareExchange(ref _setups, new MockSetups(), null);
+		return _setups!;
+	}
 
 	/// <summary>
 	///     Registers <paramref name="indexerSetup" /> for the default scenario.
@@ -88,7 +110,7 @@ public void SetupIndexer(int memberId, string scenario, IndexerSetup indexerSetu
 
 	private void AppendToIndexerMemberIdBucket(int memberId, IndexerSetup indexerSetup)
 	{
-		lock (_setupsByMemberIdLock)
+		lock (SetupsByMemberIdLock)
 		{
 			IndexerSetup[]?[]? oldTable = _indexerSetupsByMemberId;
 			int requiredLen = memberId + 1;
@@ -184,7 +206,7 @@ public void SetupMethod(int memberId, string scenario, MethodSetup methodSetup)
 
 	private void AppendToMemberIdBucket(int memberId, MethodSetup methodSetup)
 	{
-		lock (_setupsByMemberIdLock)
+		lock (SetupsByMemberIdLock)
 		{
 			MethodSetup[]?[]? oldTable = _setupsByMemberId;
 			int requiredLen = memberId + 1;
@@ -279,7 +301,7 @@ public void SetupProperty(int memberId, string scenario, PropertySetup propertyS
 
 	private void PublishPropertyToMemberIdBucket(int memberId, PropertySetup propertySetup)
 	{
-		lock (_setupsByMemberIdLock)
+		lock (SetupsByMemberIdLock)
 		{
 			PropertySetup?[]? oldTable = _propertySetupsByMemberId;
 			int requiredLen = memberId + 1;
@@ -369,7 +391,7 @@ public void SetupEvent(int memberId, string scenario, EventSetup eventSetup)
 
 	private void AppendToEventMemberIdBucket(int memberId, EventSetup eventSetup)
 	{
-		lock (_setupsByMemberIdLock)
+		lock (SetupsByMemberIdLock)
 		{
 			EventSetup[]?[]? oldTable = _eventSetupsByMemberId;
 			int requiredLen = memberId + 1;

Source/Mockolate/MockRegistry.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Threading;
 using Mockolate.Interactions;
 using Mockolate.Setup;
 
@@ -18,7 +19,7 @@ namespace Mockolate;
 public partial class MockRegistry
 {
 	[DebuggerBrowsable(DebuggerBrowsableState.Never)]
-	private readonly ScenarioState _scenarioState;
+	private ScenarioState? _scenarioState;
 
 	/// <summary>
 	///     Creates a new <see cref="MockRegistry" /> with the given <paramref name="behavior" />, a caller-provided
@@ -46,9 +47,29 @@ public MockRegistry(MockBehavior behavior, IMockInteractions interactions,
 
 		Behavior = behavior;
 		ConstructorParameters = constructorParameters;
-		Interactions = interactions;
-		Setup = new MockSetups();
-		_scenarioState = new ScenarioState();
+		_interactions = interactions;
+		Wraps = null;
+	}
+
+	/// <summary>
+	///     Creates a new <see cref="MockRegistry" /> with the given <paramref name="behavior" /> whose interaction
+	///     store is a <see cref="FastMockInteractions" /> sized to <paramref name="memberCount" />, allocated lazily
+	///     on first access.
+	/// </summary>
+	/// <remarks>
+	///     The generator-emitted <c>CreateMock</c> paths use this overload so that a mock which is only created — and
+	///     never has a member invoked or verified — never allocates an interaction store at all.
+	/// </remarks>
+	/// <param name="behavior">The <see cref="MockBehavior" /> that governs how the mock responds without a matching setup.</param>
+	/// <param name="memberCount">The number of distinct mockable members the lazily-created interaction store should hold.</param>
+	/// <param name="constructorParameters">
+	///     Values forwarded to the base-class constructor, or <see langword="null" /> if no base constructor call is needed.
+	/// </param>
+	public MockRegistry(MockBehavior behavior, int memberCount, object?[]? constructorParameters = null)
+	{
+		Behavior = behavior;
+		ConstructorParameters = constructorParameters;
+		_interactionMemberCount = memberCount;
 		Wraps = null;
 	}
 
@@ -62,9 +83,9 @@ public MockRegistry(MockRegistry registry, object wraps)
 	{
 		Behavior = registry.Behavior;
 		ConstructorParameters = registry.ConstructorParameters;
-		Interactions = new FastMockInteractions(0, registry.Behavior.SkipInteractionRecording);
-		Setup = registry.Setup;
-		_scenarioState = registry._scenarioState;
+		_interactions = new FastMockInteractions(0, registry.Behavior.SkipInteractionRecording);
+		_setups = registry.Setup;
+		_scenarioState = registry.GetOrCreateScenarioState();
 		Wraps = wraps;
 	}
 
@@ -78,9 +99,9 @@ public MockRegistry(MockRegistry registry, object?[] constructorParameters)
 	{
 		Behavior = registry.Behavior;
 		ConstructorParameters = constructorParameters;
-		Interactions = registry.Interactions;
-		Setup = registry.Setup;
-		_scenarioState = registry._scenarioState;
+		_interactions = registry.Interactions;
+		_setups = registry.Setup;
+		_scenarioState = registry.GetOrCreateScenarioState();
 		Wraps = registry.Wraps;
 	}
 
@@ -104,9 +125,9 @@ public MockRegistry(MockRegistry registry, IMockInteractions interactions)
 
 		Behavior = registry.Behavior;
 		ConstructorParameters = registry.ConstructorParameters;
-		Interactions = interactions;
-		Setup = registry.Setup;
-		_scenarioState = registry._scenarioState;
+		_interactions = interactions;
+		_setups = registry.Setup;
+		_scenarioState = registry.GetOrCreateScenarioState();
 		Wraps = registry.Wraps;
 	}
 
@@ -131,7 +152,7 @@ public MockRegistry(MockRegistry registry, IMockInteractions interactions)
 	///     Scenario setups add to, rather than replace, the default bucket - register catch-alls at the default scope
 	///     and override specific members per scenario.
 	/// </remarks>
-	public string Scenario => _scenarioState.Current;
+	public string Scenario => _scenarioState?.Current ?? "";
 
 	/// <summary>
 	///     Gets the behavior settings used by this mock instance.
@@ -166,7 +187,18 @@ public MockRegistry(MockRegistry registry, IMockInteractions interactions)
 	///     for the full resolution order.
 	/// </remarks>
 	public void TransitionTo(string scenario)
-		=> _scenarioState.Current = scenario;
+		=> GetOrCreateScenarioState().Current = scenario;
+
+	private ScenarioState GetOrCreateScenarioState()
+	{
+		if (_scenarioState is { } existing)
+		{
+			return existing;
+		}
+
+		Interlocked.CompareExchange(ref _scenarioState, new ScenarioState(), null);
+		return _scenarioState!;
+	}
 
 	private sealed class ScenarioState
 	{

Tests/Mockolate.Api.Tests/Expected/Mockolate_net10.0.txt

@@ -215,6 +215,7 @@ namespace Mockolate
         public MockRegistry(Mockolate.MockRegistry registry, object wraps) { }
         public MockRegistry(Mockolate.MockRegistry registry, object?[] constructorParameters) { }
         public MockRegistry(Mockolate.MockBehavior behavior, Mockolate.Interactions.IMockInteractions interactions, object?[]? constructorParameters = null) { }
+        public MockRegistry(Mockolate.MockBehavior behavior, int memberCount, object?[]? constructorParameters = null) { }
         public Mockolate.MockBehavior Behavior { get; }
         public object?[]? ConstructorParameters { get; }
         public Mockolate.Interactions.IMockInteractions Interactions { get; }

Tests/Mockolate.Api.Tests/Expected/Mockolate_net8.0.txt

@@ -202,6 +202,7 @@ namespace Mockolate
         public MockRegistry(Mockolate.MockRegistry registry, object wraps) { }
         public MockRegistry(Mockolate.MockRegistry registry, object?[] constructorParameters) { }
         public MockRegistry(Mockolate.MockBehavior behavior, Mockolate.Interactions.IMockInteractions interactions, object?[]? constructorParameters = null) { }
+        public MockRegistry(Mockolate.MockBehavior behavior, int memberCount, object?[]? constructorParameters = null) { }
         public Mockolate.MockBehavior Behavior { get; }
         public object?[]? ConstructorParameters { get; }
         public Mockolate.Interactions.IMockInteractions Interactions { get; }

Tests/Mockolate.Api.Tests/Expected/Mockolate_netstandard2.0.txt

@@ -177,6 +177,7 @@ namespace Mockolate
         public MockRegistry(Mockolate.MockRegistry registry, object wraps) { }
         public MockRegistry(Mockolate.MockRegistry registry, object?[] constructorParameters) { }
         public MockRegistry(Mockolate.MockBehavior behavior, Mockolate.Interactions.IMockInteractions interactions, object?[]? constructorParameters = null) { }
+        public MockRegistry(Mockolate.MockBehavior behavior, int memberCount, object?[]? constructorParameters = null) { }
         public Mockolate.MockBehavior Behavior { get; }
         public object?[]? ConstructorParameters { get; }
         public Mockolate.Interactions.IMockInteractions Interactions { get; }

Tests/Mockolate.SourceGenerators.Tests/Snapshot/Expected/BaseClass_WithMultipleAdditionalInterfaces_CanBeCreated/Mock.ComprehensiveAbstractClass.g.cs

@@ -40,7 +40,7 @@ internal class ComprehensiveAbstractClass :
 		/// </summary>
 		private static global::Mockolate.MockRegistry MockolateCreateRegistryFromBehavior(global::Mockolate.MockBehavior behavior)
 		{
-			global::Mockolate.MockRegistry registry = new global::Mockolate.MockRegistry(behavior, CreateFastInteractions(behavior));
+			global::Mockolate.MockRegistry registry = new global::Mockolate.MockRegistry(behavior, MemberCount);
 			MockRegistryProvider.Value = registry;
 			return registry;
 		}
@@ -943,7 +943,7 @@ internal static partial class MockExtensionsForComprehensiveAbstractClass
 			}
 
 			mockBehavior ??= global::Mockolate.MockBehavior.Default;
-			global::Mockolate.MockRegistry mockRegistry = new global::Mockolate.MockRegistry(mockBehavior, global::Mockolate.Mock.ComprehensiveAbstractClass.CreateFastInteractions(mockBehavior), constructorParameters);
+			global::Mockolate.MockRegistry mockRegistry = new global::Mockolate.MockRegistry(mockBehavior, global::Mockolate.Mock.ComprehensiveAbstractClass.MemberCount, constructorParameters);
 			return CreateMockInstance(mockRegistry, constructorParameters, setup);
 		}
 

Tests/Mockolate.SourceGenerators.Tests/Snapshot/Expected/BaseClass_WithMultipleAdditionalInterfaces_CanBeCreated/Mock.ICombinationMockA.g.cs

@@ -39,7 +39,7 @@ internal class ICombinationMockA :
 		/// </summary>
 		private static global::Mockolate.MockRegistry MockolateCreateRegistryFromBehavior(global::Mockolate.MockBehavior behavior)
 		{
-			global::Mockolate.MockRegistry registry = new global::Mockolate.MockRegistry(behavior, CreateFastInteractions(behavior));
+			global::Mockolate.MockRegistry registry = new global::Mockolate.MockRegistry(behavior, MemberCount);
 			return registry;
 		}
 
@@ -544,7 +544,7 @@ internal static partial class MockExtensionsForICombinationMockA
 			}
 
 			mockBehavior ??= global::Mockolate.MockBehavior.Default;
-			global::Mockolate.MockRegistry mockRegistry = new global::Mockolate.MockRegistry(mockBehavior, global::Mockolate.Mock.ICombinationMockA.CreateFastInteractions(mockBehavior), constructorParameters);
+			global::Mockolate.MockRegistry mockRegistry = new global::Mockolate.MockRegistry(mockBehavior, global::Mockolate.Mock.ICombinationMockA.MemberCount, constructorParameters);
 			return CreateMockInstance(mockRegistry, constructorParameters, setup);
 		}