fix thread safety of Pools, minor FishTable improvements

Source/FisheryLib/Pools/FishPool.cs

@@ -9,29 +9,96 @@ namespace FisheryLib.Pools;
 
 public static class FishPool<T> where T : IFishPoolable
 {
-	private static T?[] _freeItems = new T[4];
-	private static int _freeItemCount;
+	[ThreadStatic]
+	private static T?[]? _itemsThreadStatic;
+
+	[ThreadStatic]
+	private static int _itemCountThreadStatic;
+
+	private static object _lockObject = new();
+	private static T?[] _itemsGlobal = new T[16];
+	private static int _itemCountGlobal;
 
 	public static T Get()
 	{
-		if (_freeItemCount == 0)
-			return Reflection.New<T>();
+		if (_itemCountThreadStatic == 0)
+			FetchThroughLock();
+
+		ref var itemBucket = ref _itemsThreadStatic![--_itemCountThreadStatic];
+		var item = itemBucket;
+		itemBucket = default;
+		return item!;
+	}
+
+	[MethodImpl(MethodImplOptions.NoInlining)]
+	private static void FetchThroughLock()
+	{
+		var itemsThreadStatic = _itemsThreadStatic ??= InitializeItemsThreadStatic();
+		var createNew = false;
 		
-		var freeItem = _freeItems[--_freeItemCount];
-		_freeItems[_freeItemCount] = default;
-		return freeItem!;
+		lock (_lockObject)
+		{
+			if (_itemCountGlobal != 0)
+			{
+				for (var i = 8; i-- > 0;)
+				{
+					itemsThreadStatic[i] = _itemsGlobal[--_itemCountGlobal];
+					_itemsGlobal[_itemCountGlobal] = default;
+				}
+			}
+			else
+			{
+				createNew = true;
+			}
+		}
+
+		if (createNew)
+		{
+			for (var i = 8; i-- > 0;)
+				itemsThreadStatic[i] = Reflection.New<T>();
+		}
+		
+		_itemCountThreadStatic = 8;
 	}
 
 	public static void Return(T item)
 	{
 		item.Reset();
-		
-		if (++_freeItemCount >= _freeItems.Length)
-			ExpandFreeItems();
 
-		_freeItems[_freeItemCount - 1] = item;
+		var itemsThreadStatic = _itemsThreadStatic ??= InitializeItemsThreadStatic();
+		
+		if (_itemCountThreadStatic == 16)
+			PushThroughLock();
+
+		itemsThreadStatic[_itemCountThreadStatic++] = item;
 	}
 
 	[MethodImpl(MethodImplOptions.NoInlining)]
-	private static void ExpandFreeItems() => Array.Resize(ref _freeItems, _freeItems.Length << 1);
+	private static void PushThroughLock()
+	{
+		var itemsThreadStatic = _itemsThreadStatic!;
+		
+		lock (_lockObject)
+		{
+			if (_itemCountGlobal + 8 > _itemsGlobal.Length)
+				ExpandGlobalItems();
+			
+			for (var i = 16; i-- > 8;)
+			{
+				ref var itemBucket = ref itemsThreadStatic[i];
+				var item = itemBucket;
+				itemBucket = default;
+
+				_itemsGlobal[_itemCountGlobal++] = item;
+			}
+		}
+		
+		_itemCountThreadStatic = 8;
+	}
+
+	[MethodImpl(MethodImplOptions.NoInlining)]
+	private static T?[] InitializeItemsThreadStatic() => new T?[16];
+
+	[MethodImpl(MethodImplOptions.NoInlining)]
+	private static void ExpandGlobalItems() => Array.Resize(ref _itemsGlobal, _itemsGlobal.Length << 1);
 }