Versioning implemented in RecyclableList<T>

README.md

@@ -142,6 +142,10 @@
     1. 🅿️ Review locks
     1. 🅿️ Measure multi-threading performance
     1. 🅿️ Implement memory bucket disposal in high RAM pressure scenario
+1. 🅿️ Optimize `RecyclableCollectionVersionObjectPool`
+    1. 🅿️ Implement custom `ObjectPool<T>`
+    1. 🅿️ Measure multi-threading performance
+    1. 🅿️ Implement memory bucket disposal in high RAM pressure scenario
 1. 🅿️ Review `RecyclableArrayPool`
     1. 🅿️ Review locks
     1. 🅿️ Measure multi-threading performance
@@ -166,9 +170,10 @@
     1. 🅿️ `RecyclableLongListExtensions.CopyTo`
 1. 🅿️ Cleanup
     1. 🅿️ Replace `LastBlockWithData` property with `_lastBlockWithData` field
-    1. ✅ Cleanup `RecyclableLongListExtensions`
+    1. ✅ `RecyclableLongListExtensions`
     1. ✅ `ListExtensions`
     1. 🅿️ `MathUtils`
+    1. 🅿️ Resolve TODOs
 1. 🅿️ Optimize
     1. 🅿️ `ListExtensions`
     1. 🅿️ `MathUtils`

Recyclable.Collections/Pools/RecyclableCollectionVersionPool.cs

@@ -0,0 +1,20 @@
+using Microsoft.Extensions.ObjectPool;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Recyclable.Collections.Pools
+{
+	public class RecyclableCollectionVersionPool
+	{
+		private static readonly RecyclableCollectionVersionPool _shared = new();
+		public static RecyclableCollectionVersionPool Shared => _shared;
+
+		private ObjectPool<RecyclableCollectionVersion> _pool = new DefaultObjectPool<RecyclableCollectionVersion>(new DefaultPooledObjectPolicy<RecyclableCollectionVersion>());
+
+		public RecyclableCollectionVersion Get() => _pool.Get().Reset();
+		public void Return(RecyclableCollectionVersion version) => _pool.Return(version);
+	}
+}

Recyclable.Collections/RecyclableCollectionVersion.cs

@@ -0,0 +1,41 @@
+using System.Runtime.CompilerServices;
+
+namespace Recyclable.Collections
+{
+	public sealed class RecyclableCollectionVersion
+	{
+		private ulong _enumeratorCount;
+		public ulong Version;
+		public bool IsVersioned;
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public void Inc() => _ = unchecked(Version++);
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public void AddEnumerator()
+		{
+			if (unchecked(_enumeratorCount++) == 0)
+			{
+				IsVersioned = true;
+			}
+		}
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public void RemoveEnumerator()
+		{
+			if (unchecked(--_enumeratorCount) == 0)
+			{
+				IsVersioned = false;
+			}
+		}
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public RecyclableCollectionVersion Reset()
+		{
+			IsVersioned = false;
+			Version = 0;
+			_enumeratorCount = 0;
+			return this;
+		}
+	}
+}

Recyclable.Collections/RecyclableList.Enumerator.cs

@@ -0,0 +1,79 @@
+using System.Collections;
+
+namespace Recyclable.Collections
+{
+	public class RecyclableListEnumerator<T> : IEnumerator<T>
+	{
+		private static void ThrowListModifiedException() => throw new InvalidOperationException("Can't move to the next item, because the collection was modified. You must restart the enumeration by calling Reset(), if you want to enumerate the collection again");
+
+		private int _currentIndex = RecyclableDefaults.ItemNotFoundIndex;
+		private RecyclableList<T>? _list;
+		private RecyclableCollectionVersion? _listVersion;
+		private ulong _version;
+
+		private T? _current;
+
+		public RecyclableListEnumerator(RecyclableList<T> list)
+		{
+			_list = list;
+			_listVersion = list._version;
+			_listVersion!.AddEnumerator();
+			_version = _listVersion!.Version;
+		}
+
+		public T Current => _current ?? throw new InvalidOperationException("The enumerator wasn't initialized. You need to call MoveNext() before getting the current iterator value");
+		object? IEnumerator.Current => _current;
+
+		public void Dispose()
+		{
+			if (_listVersion != null)
+			{
+				_listVersion.RemoveEnumerator();
+				_listVersion = null;
+			}
+
+			if (_list != null)
+			{
+				_list = null;
+			}
+
+			GC.SuppressFinalize(this);
+		}
+
+		public bool MoveNext()
+		{
+			if (_list != null)
+			{
+				if (_list._version!.Version != _version)
+				{
+					ThrowListModifiedException();
+					return false;
+				}
+				else if (_currentIndex < _list.Count - 1)
+				{
+					_currentIndex++;
+					_current = _list[_currentIndex];
+					return true;
+				}
+				else
+				{
+					return false;
+				}
+			}
+			else
+			{
+				return false;
+			}
+		}
+
+		public void Reset()
+		{
+			_currentIndex = RecyclableDefaults.ItemNotFoundIndex;
+			_current = default;
+			if (_list != null)
+			{
+				_version = _list._version!.Version;
+			}
+		}
+	}
+}

Recyclable.Collections/RecyclableList.cs

@@ -1,4 +1,5 @@
-using System.Buffers;
+using Recyclable.Collections.Pools;
+using System.Buffers;
 using System.Collections;
 using System.Runtime.CompilerServices;
 
@@ -9,10 +10,65 @@ namespace Recyclable.Collections
 		private static readonly ArrayPool<T> _arrayPool = ArrayPool<T>.Create();
 		private static readonly bool _defaultIsNull = default(T) == null;
 		protected static readonly bool NeedsClearing = !typeof(T).IsValueType;
-		public static explicit operator ReadOnlySpan<T>(RecyclableList<T> source) => new(source._memoryBlock, 0, source.Count);
-		protected T[] _memoryBlock;
-
+	
 		private static void ThrowArgumentOutOfRangeException(in string argumentName, in string message) => throw new ArgumentOutOfRangeException(argumentName, message);
+		public static explicit operator ReadOnlySpan<T>(RecyclableList<T> source) => new(source._memoryBlock, 0, source.Count);
+
+		protected T[] _memoryBlock;
+		internal RecyclableCollectionVersion? _version;
+
+		public RecyclableCollectionVersion? Version => _version;
+
+		protected IEnumerator<T> AddRangeEnumerated(IEnumerable<T> source, int growByCount)
+		{
+			int targetItemIdx = _count;
+			Span<T> memorySpan;
+
+			int i;
+			var enumerator = source.GetEnumerator();
+
+			int capacity = _capacity;
+			memorySpan = new(_memoryBlock);
+			if (enumerator.MoveNext())
+			{
+				int available = capacity - targetItemIdx;
+				do
+				{
+					if (targetItemIdx + growByCount > capacity)
+					{
+						capacity = EnsureCapacity(this, capacity + growByCount);
+						memorySpan = new(_memoryBlock);
+						available = capacity - targetItemIdx;
+					}
+
+					for (i = 0; i < available; i++)
+					{
+						memorySpan[targetItemIdx++] = enumerator.Current;
+						if (!enumerator.MoveNext())
+						{
+							break;
+						}
+					}
+				}
+				while (i >= available);
+			}
+
+			_count = targetItemIdx;
+			return enumerator;
+		}
+
+		protected void AddRangeWithKnownCount(IEnumerable<T> source, int targetItemIdx, int requiredAdditionalCapacity)
+		{
+			_ = EnsureCapacity(this, targetItemIdx + requiredAdditionalCapacity);
+
+			Span<T> memorySpan = new(_memoryBlock);
+			foreach (var item in source)
+			{
+				memorySpan[targetItemIdx++] = item;
+			}
+
+			_count = targetItemIdx;
+		}
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
 		protected static T[] Resize(in T[]? source, int newSize)
@@ -137,7 +193,15 @@ namespace Recyclable.Collections
 			get => _memoryBlock[index];
 
 			[MethodImpl(MethodImplOptions.AggressiveInlining)]
-			set => _memoryBlock[index] = value;
+			set
+			{
+				_memoryBlock[index] = value;
+
+				if (_version?.IsVersioned ?? false)
+				{
+					_version.Inc();
+				}
+			}
 		}
 
 		protected int _capacity;
@@ -151,6 +215,11 @@ namespace Recyclable.Collections
 					_memoryBlock = Resize(_memoryBlock, value);
 					_capacity = _memoryBlock.Length;
 				}
+
+				if (_version?.IsVersioned ?? false)
+				{
+					_version.Inc();
+				}
 			}
 		}
 
@@ -161,10 +230,19 @@ namespace Recyclable.Collections
 			get => _count;
 
 			[MethodImpl(MethodImplOptions.AggressiveInlining)]
-			set => _count = value;
+			// TODO: Clear items if we're decreasing the size of the list, if T is reference type
+			set
+			{
+				_count = value;
+
+				if (_version?.IsVersioned ?? false)
+				{
+					_version.Inc();
+				}
+			}
 		}
 
-		public bool IsReadOnly { get; } = false;
+		public bool IsReadOnly => false;
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
 		public void Add(T item)
@@ -176,6 +254,11 @@ namespace Recyclable.Collections
 			}
 
 			_memoryBlock[_count++] = item;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -197,6 +280,11 @@ namespace Recyclable.Collections
 			Span<T> itemsSpan = new(items);
 			itemsSpan.CopyTo(targetSpan);
 			_count = targetCapacity;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -217,6 +305,11 @@ namespace Recyclable.Collections
 			var targetSpan = new Span<T>(_memoryBlock, _count, sourceItemsCount);
 			itemsSpan.CopyTo(targetSpan);
 			_count = targetCapacity;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -236,6 +329,11 @@ namespace Recyclable.Collections
 
 			items.CopyTo(_memoryBlock, _count);
 			_count = targetCapacity;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -255,6 +353,11 @@ namespace Recyclable.Collections
 
 			items.CopyTo(_memoryBlock, _count);
 			_count = targetCapacity;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -276,6 +379,11 @@ namespace Recyclable.Collections
 			Span<T> itemsSpan = new(items._memoryBlock, 0, sourceItemsCount);
 			itemsSpan.CopyTo(targetSpan);
 			_count = targetCapacity;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -329,6 +437,11 @@ namespace Recyclable.Collections
 			}
 
 			_count = targetCapacity;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
@@ -337,72 +450,37 @@ namespace Recyclable.Collections
 			if (source is T[] sourceArray)
 			{
 				AddRange(sourceArray);
-				return;
 			}
-
-			if (source is List<T> sourceList)
+			else if (source is List<T> sourceList)
 			{
 				AddRange(sourceList);
-				return;
 			}
-
-			if (source is RecyclableList<T> sourceRecyclableList)
+			else if (source is RecyclableList<T> sourceRecyclableList)
 			{
 				AddRange(sourceRecyclableList);
-				return;
 			}
-
-			if (source is IList<T> sourceIList)
+			else if (source is IList<T> sourceIList)
 			{
 				AddRange(sourceIList);
-				return;
 			}
-
-			int targetItemIdx = _count;
-			Span<T> memorySpan;
-			if (source.TryGetNonEnumeratedCount(out var requiredAdditionalCapacity))
+			else if (source.TryGetNonEnumeratedCount(out var requiredAdditionalCapacity))
 			{
-				_ = EnsureCapacity(this, targetItemIdx + requiredAdditionalCapacity);
-				memorySpan = new(_memoryBlock);
-				foreach (var item in source)
+				AddRangeWithKnownCount(source, _count, requiredAdditionalCapacity);
+
+				if (_version?.IsVersioned ?? false)
 				{
-					memorySpan[targetItemIdx++] = item;
+					_version.Inc();
 				}
-
-				_count = targetItemIdx;
-				return;
 			}
-
-			int i;
-			using var enumerator = source.GetEnumerator();
-
-			int capacity = _capacity;
-			memorySpan = new(_memoryBlock);
-			if (enumerator.MoveNext())
+			else
 			{
-				int available = capacity - targetItemIdx;
-				do
+				AddRangeEnumerated(source, growByCount);
+
+				if (_version?.IsVersioned ?? false)
 				{
-					if (targetItemIdx + growByCount > capacity)
-					{
-						capacity = EnsureCapacity(this, capacity + growByCount);
-						memorySpan = new(_memoryBlock);
-						available = capacity - targetItemIdx;
-					}
-
-					for (i = 0; i < available; i++)
-					{
-						memorySpan[targetItemIdx++] = enumerator.Current;
-						if (!enumerator.MoveNext())
-						{
-							break;
-						}
-					}
+					_version.Inc();
 				}
-				while (i >= available);
 			}
-
-			_count = targetItemIdx;
 		}
 
 		public T[] AsArray => _memoryBlock;
@@ -416,6 +494,11 @@ namespace Recyclable.Collections
 			}
 
 			_count = 0;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -424,16 +507,6 @@ namespace Recyclable.Collections
 		[MethodImpl(MethodImplOptions.NoInlining)]
 		public void CopyTo(T[] array, int index) => Array.Copy(_memoryBlock, 0, array, index, _count);
 
-		protected static IEnumerable<T> Enumerate(RecyclableList<T> list)
-		{
-			int count = list._count;
-			var memory = list._memoryBlock;
-			for (var i = 0; i < count; i++)
-			{
-				yield return memory[i];
-			}
-		}
-
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
 		public int IndexOf(T itemToFind) => _count > 0 ? Array.IndexOf(_memoryBlock, itemToFind, 0, _count) : RecyclableDefaults.ItemNotFoundIndex;
 
@@ -456,6 +529,11 @@ namespace Recyclable.Collections
 
 			_memoryBlock[index] = item;
 			_count++;
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
@@ -477,6 +555,11 @@ namespace Recyclable.Collections
 #pragma warning restore CS8601
 				}
 
+				if (_version?.IsVersioned ?? false)
+				{
+					_version.Inc();
+				}
+
 				return true;
 			}
 
@@ -503,13 +586,26 @@ namespace Recyclable.Collections
 				_memoryBlock[_count] = default;
 #pragma warning restore CS8601
 			}
+
+			if (_version?.IsVersioned ?? false)
+			{
+				_version.Inc();
+			}
 		}
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		public IEnumerator<T> GetEnumerator() => Enumerate(this).GetEnumerator();
+		public IEnumerator<T> GetEnumerator()
+		{
+			_version ??= RecyclableCollectionVersionPool.Shared.Get();
+			return new RecyclableListEnumerator<T>(this);
+		}
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		IEnumerator IEnumerable.GetEnumerator() => Enumerate(this).GetEnumerator();
+		IEnumerator IEnumerable.GetEnumerator()
+		{
+			_version ??= RecyclableCollectionVersionPool.Shared.Get();
+			return new RecyclableListEnumerator<T>(this);
+		}
 
 		public void Dispose()
 		{
@@ -522,6 +618,13 @@ namespace Recyclable.Collections
 					_arrayPool.Return(_memoryBlock, NeedsClearing);
 				}
 
+				if (_version != null)
+				{
+					var toReturn = _version;
+					_version = null;
+					RecyclableCollectionVersionPool.Shared.Return(toReturn);
+				}
+
 				GC.SuppressFinalize(this);
 			}
 		}