Refactoring ObjectSpace(s) to support Persistence Ignorance (PI)

src/Hydrogen (Win).sln

@@ -92,6 +92,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Misc", "Misc", "{AA4A8AEA-0
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HashLib4CSharp.Tests", "..\tests\HashLib4CSharp.Tests\HashLib4CSharp.Tests.csproj", "{9A1EF7C9-A988-0039-A0DB-D84F5F25BD0D}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Hydrogen.Generators", "Hydrogen.Generators\Hydrogen.Generators.csproj", "{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -404,6 +406,14 @@ Global
 		{9A1EF7C9-A988-0039-A0DB-D84F5F25BD0D}.Release|Any CPU.Build.0 = Release|Any CPU
 		{9A1EF7C9-A988-0039-A0DB-D84F5F25BD0D}.Release|x86.ActiveCfg = Release|Any CPU
 		{9A1EF7C9-A988-0039-A0DB-D84F5F25BD0D}.Release|x86.Build.0 = Release|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Debug|x86.Build.0 = Debug|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Release|x86.ActiveCfg = Release|Any CPU
+		{E4B09863-F1C9-4AEC-83CA-DAD3D13A7478}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/Hydrogen.Generators/Class1.cs

@@ -0,0 +1,14 @@
+using System.ComponentModel;
+
+namespace Hydrogen.Generators {
+
+	public interface IObjectSpaceObject : INotifyPropertyChanging, INotifyPropertyChanged {
+		bool Dirty { get; set; }
+	}
+
+	public class Class1 : INotifyPropertyChanging, INotifyPropertyChanged {
+
+		public event PropertyChangingEventHandler? PropertyChanging;
+		public event PropertyChangedEventHandler? PropertyChanged;
+	}
+}

src/Hydrogen.Generators/Hydrogen.Generators.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

src/Hydrogen/ObjectSpaces/Builder/IObjectSpaceDimensionBuilder.cs

@@ -32,6 +32,8 @@ public interface IObjectSpaceDimensionBuilder {
 
 	IObjectSpaceDimensionBuilder WithUniqueIndexOn(Member member, string indexName = null, IndexNullPolicy nullPolicy = IndexNullPolicy.IgnoreNull);
 
+	IObjectSpaceDimensionBuilder WithChangeTrackingVia(Member member);
+
 	IObjectSpaceDimensionBuilder OptimizeAssumingAverageItemSize(int bytes);
 
 	ObjectSpaceDefinition.DimensionDefinition BuildDefinition();

src/Hydrogen/ObjectSpaces/Builder/ObjectSpaceBuilder.cs

@@ -41,6 +41,7 @@ public class ObjectSpaceBuilder {
 	private ComparerFactory _comparerFactory;
 	private bool _usingCustomComparerFactory;
 	private bool _specifiedCustomComparer;
+	private bool _autoSave;
 
 	public ObjectSpaceBuilder() {
 		_type = null;
@@ -64,6 +65,8 @@ public ObjectSpaceBuilder() {
 		_comparerFactory = new ComparerFactory(ComparerFactory.Default);
 		_usingCustomComparerFactory = false;
 		_specifiedCustomComparer = false;
+
+		_autoSave = false;
 	}
 
 	public ObjectSpaceBuilder UseFile(string filePath) {
@@ -125,6 +128,11 @@ public ObjectSpaceBuilder WithEndianness(Endianness endianness) {
 		return this;
 	}
 
+	public ObjectSpaceBuilder AutoSave() {
+		_autoSave = true;
+		return this;
+	}
+
 	public ObjectSpaceBuilder Merkleized() {
 		_merkleized = true;
 		foreach(var dimension in _dimensions) {
@@ -252,8 +260,7 @@ public ObjectSpaceDimensionBuilder<T> Configure<T>() {
 	}	
 
 	public ObjectSpaceDefinition BuildDefinition() {
-		var definition = new ObjectSpaceDefinition {
-			Merkleized = _merkleized,
+		var definition = new ObjectSpaceDefinition(_merkleized, _autoSave) {
 			HashFunction = _hashFunction,
 			Dimensions = _dimensions.Select(x => x.BuildDefinition()).ToArray()
 		};

src/Hydrogen/ObjectSpaces/Builder/ObjectSpaceDimensionBuilder.cs

@@ -18,11 +18,13 @@ public class ObjectSpaceDimensionBuilder<T> : IObjectSpaceDimensionBuilder {
 	protected readonly ObjectSpaceBuilder _parent;
 	private readonly IList<ObjectSpaceDefinition.IndexDefinition> _indexes;
 	private int? _averageItemSize;
+	private ObjectChangeTracker _changeTracker;
 
 	public ObjectSpaceDimensionBuilder(ObjectSpaceBuilder parent) {
 		_parent = parent;
 		_averageItemSize = null;
 		_indexes = new List<ObjectSpaceDefinition.IndexDefinition>();
+		_changeTracker = ObjectChangeTracker.Default;
 
 		// Add recyclable free index store by default
 		WithRecyclableIndexes();
@@ -127,6 +129,7 @@ public ObjectSpaceDimensionBuilder<T> WithUniqueIndexOn<TMember>(Expression<Func
 	public ObjectSpaceDimensionBuilder<T> WithUniqueIndexOn(Member member, string indexName = null, IndexNullPolicy nullPolicy = IndexNullPolicy.IgnoreNull) 
 		=> (ObjectSpaceDimensionBuilder<T>)((IObjectSpaceDimensionBuilder)this).WithUniqueIndexOn(member, indexName, nullPolicy);
 
+
 	IObjectSpaceDimensionBuilder IObjectSpaceDimensionBuilder.WithUniqueIndexOn(Member member, string indexName = null, IndexNullPolicy nullPolicy = IndexNullPolicy.IgnoreNull) {
 		Guard.ArgumentNotNull(member, nameof(member));
 		Guard.Argument(member.DeclaringType == typeof(T), nameof(member), $"Not a member of {typeof(T).ToStringCS()}");
@@ -160,6 +163,14 @@ public ObjectSpaceDimensionBuilder<T> Merkleized(string indexName = null) {
 		return this;
 	}
 
+	public ObjectSpaceDimensionBuilder<T> WithChangeTrackingVia<TMember>(Expression<Func<T, TMember>> memberExpression) 
+		=> (ObjectSpaceDimensionBuilder<T>)WithChangeTrackingVia(memberExpression.ToMember());
+
+	public IObjectSpaceDimensionBuilder WithChangeTrackingVia(Member member) {
+		_changeTracker = new ObjectChangeTracker(member);
+		return this;
+	}
+
 	public ObjectSpaceDimensionBuilder<T> OptimizeAssumingAverageItemSize(int bytes) {
 		_averageItemSize = bytes;
 		return this;
@@ -175,7 +186,8 @@ public ObjectSpaceDefinition.DimensionDefinition BuildDefinition() {
 		return new ObjectSpaceDefinition.DimensionDefinition {
 			ObjectType = typeof(T),
 			AverageObjectSizeBytes = _averageItemSize,
-			Indexes = _indexes.ToArray()
+			Indexes = _indexes.ToArray(),
+			ChangeTracker = _changeTracker
 		};
 	}
 

src/Hydrogen/ObjectSpaces/FileObjectSpace.cs

@@ -21,7 +21,7 @@ public class FileObjectSpace : ObjectSpaceBase, ITransactionalObject{
 	private readonly TransactionalStream _fileStream;
 
 	public FileObjectSpace(HydrogenFileDescriptor file, ObjectSpaceDefinition objectSpaceDefinition, SerializerFactory serializerFactory, ComparerFactory comparerFactory, FileAccessMode accessMode = FileAccessMode.Default)
-		: base(CreateStreams(file, objectSpaceDefinition.Merkleized, accessMode, out var fileStream), objectSpaceDefinition, serializerFactory, comparerFactory, accessMode) {
+		: base(CreateStreams(file, objectSpaceDefinition.Traits.HasFlag(ObjectSpaceTraits.Merkleized), accessMode, out var fileStream), objectSpaceDefinition, serializerFactory, comparerFactory, accessMode) {
 		Guard.ArgumentNotNull(file, nameof(file));
 		Guard.ArgumentNotNull(objectSpaceDefinition, nameof(objectSpaceDefinition));
 		Guard.ArgumentNotNull(serializerFactory, nameof(serializerFactory));
@@ -30,6 +30,8 @@ public FileObjectSpace(HydrogenFileDescriptor file, ObjectSpaceDefinition object
 		File = file;
 		AccessMode = accessMode;
 
+		FlushOnDispose = false; // this flushes on Commiting event, on Dispose we don't want to risk changing the file (Rollback scenario)
+
 		// Create the file stream
 		_fileStream = fileStream;
 		SubscribeToFileStreamEvents();
@@ -60,7 +62,7 @@ private static ClusteredStreams CreateStreams(HydrogenFileDescriptor file, bool
 
 	public void Commit()  {
 		using (EnterAccessScope()) {
-			// flush all cached changes
+			// flush all changed (stored in uncommitted pages)
 			_fileStream.Commit();
 		}
 	}

src/Hydrogen/ObjectSpaces/InstanceTracker.cs

@@ -8,19 +8,20 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace Hydrogen.ObjectSpaces;
 
 /// <summary>
-///  Used to track instances of fetched objects within an <see cref="ObjectSpace"/>.
+///  Used to track instances of fetched objects within an <see cref="ObjectSpaceBase"/>.
 /// </summary>
 /// <remarks>Not thread-safe by design</remarks>
 internal class InstanceTracker {
 
-	private readonly Dictionary<Type, BijectiveDictionary<long, object>> _objects;
+	private readonly Dictionary<Type, BijectiveDictionary<long, object>> _objectsByType;
 
 	public InstanceTracker() {
-		_objects = new Dictionary<Type, BijectiveDictionary<long, object>>(TypeEquivalenceComparer.Instance);
+		_objectsByType = new Dictionary<Type, BijectiveDictionary<long, object>>(TypeEquivalenceComparer.Instance);
 	}
 
 
@@ -40,7 +41,7 @@ public bool TryGet<TItem>(long index, out TItem item) {
 	}
 
 	public bool TryGet(Type itemType, long index, out object item) {
-		if (!_objects.TryGetValue(itemType, out var instances)) {
+		if (!_objectsByType.TryGetValue(itemType, out var instances)) {
 			item = default;
 			return false;
 		}
@@ -51,13 +52,20 @@ public bool TryGet(Type itemType, long index, out object item) {
 		return true;
 	}
 
+	public IEnumerable<object> GetInstances() 
+		=> _objectsByType.Values.SelectMany(instances => instances.Values);
+
+
+	public IEnumerable<object> GetInstances(Type itemType) 
+		=> _objectsByType.TryGetValue(itemType, out var instances) ? instances.Values : Array.Empty<object>();
+
 
 	public void Track(object item, long index) {
 		var itemType = item.GetType();
 
-		if (!_objects.TryGetValue(itemType, out var instances)) {
+		if (!_objectsByType.TryGetValue(itemType, out var instances)) {
 			instances = CreateInstanceDictionary();
-			_objects.Add(itemType, instances);
+			_objectsByType.Add(itemType, instances);
 		}
 
 		if (instances.TryGetValue(index, out var _)) 
@@ -69,12 +77,12 @@ public void Track(object item, long index) {
 	public void Untrack(object item) {
 		var itemType = item.GetType();
 
-		if (!_objects.TryGetValue(itemType, out var instances) || !instances.TryGetKey(item, out var index)) 
+		if (!_objectsByType.TryGetValue(itemType, out var instances) || !instances.TryGetKey(item, out var index)) 
 			throw new InvalidOperationException("Object instance was not tracked");
 
 		instances.Remove(index);
 		if (instances.Count == 0)
-			_objects.Remove(itemType);
+			_objectsByType.Remove(itemType);
 	}
 
 	public long GetIndexOf(object item) {
@@ -86,7 +94,7 @@ public long GetIndexOf(object item) {
 	public bool TryGetIndexOf(object item, out long index) {
 		var itemType = item.GetType();
 
-		if (!_objects.TryGetValue(itemType, out var instances)) {
+		if (!_objectsByType.TryGetValue(itemType, out var instances)) {
 			index = default;
 			return false;
 		}
@@ -98,7 +106,7 @@ public bool TryGetIndexOf(object item, out long index) {
 	}
 
 	public void Clear() {
-		_objects.Clear();
+		_objectsByType.Clear();
 	}
 
 	private BijectiveDictionary<long, object> CreateInstanceDictionary() => new(EqualityComparer<long>.Default, ReferenceEqualityComparer.Instance);

src/Hydrogen/ObjectSpaces/MemoryObjectSpace.cs

@@ -32,7 +32,7 @@ public MemoryObjectSpace(
 		int clusterSize = HydrogenDefaults.ClusterSize, 
 		ClusteredStreamsPolicy clusteredStreamsPolicy = HydrogenDefaults.ContainerPolicy, 
 		Endianness endianness = HydrogenDefaults.Endianness
-	) : base(CreateStreams(memoryStream, clusterSize, clusteredStreamsPolicy, endianness, objectSpaceDefinition.Merkleized), objectSpaceDefinition, serializerFactory, comparerFactory) {
+	) : base(CreateStreams(memoryStream, clusterSize, clusteredStreamsPolicy, endianness, objectSpaceDefinition.Traits.HasFlag(ObjectSpaceTraits.Merkleized)), objectSpaceDefinition, serializerFactory, comparerFactory) {
 		Guard.ArgumentNotNull(objectSpaceDefinition, nameof(objectSpaceDefinition));
 		Guard.ArgumentNotNull(serializerFactory, nameof(serializerFactory));
 		Guard.ArgumentNotNull(comparerFactory, nameof(comparerFactory));

src/Hydrogen/ObjectSpaces/ObjectChangeTracker.cs

@@ -0,0 +1,44 @@
+using System;
+using Hydrogen.Mapping;
+
+namespace Hydrogen.ObjectSpaces;
+
+internal class ObjectChangeTracker {
+
+	public ObjectChangeTracker()  {
+		HasChanged = _ => false;;
+		SetChanged = (_, _) => { };
+		SupportsChangeTracking = false;
+	}
+
+	public ObjectChangeTracker(Member member) 
+		: this(Guard.EnsureCast<PropertyMember>(member, $"Must be a {nameof(PropertyMember)}")) {
+	}
+
+	public ObjectChangeTracker(PropertyMember member) {
+		Guard.ArgumentNotNull(member, nameof(member));
+		Guard.Ensure(member.CanRead, "Member must have public getter");
+		Guard.Ensure(member.CanWrite, "Member must have public setter");
+		Guard.Ensure(member.PropertyType == typeof(bool), "Member must be of type bool");
+		HasChanged = obj => (bool)member.GetValue(obj);
+		SetChanged = (obj, val) => member.SetValue(obj, val);
+		SupportsChangeTracking = true;
+	}
+
+	public ObjectChangeTracker(Func<object, bool> hasChanged, Action<object, bool> setChanged) {
+		Guard.ArgumentNotNull(hasChanged, nameof(hasChanged));
+		Guard.ArgumentNotNull(setChanged, nameof(setChanged));
+		HasChanged = hasChanged;
+		SetChanged = setChanged;
+		SupportsChangeTracking = true;
+	}
+
+	public bool SupportsChangeTracking { get; }
+
+	public Func<object, bool> HasChanged { get; }
+
+	public Action<object, bool> SetChanged { get; }
+
+	public static ObjectChangeTracker Default { get; } = new ();
+
+}