RecyclableList.IndexOf parallel performance improvements.

Recyclable.Collections/Pools/RecyclableArrayPool.cs

@@ -0,0 +1,35 @@
+using System.Buffers;
+using System.Collections.Concurrent;
+
+namespace Recyclable.Collections.Pools
+{
+    public static class RecyclableArrayPool<T>
+	{
+		public static readonly OneSizeArrayPool<T> Null = new(0, 0);
+
+		private static readonly ConcurrentDictionary<int, ArrayPool<T>> _pools = new();
+
+		public static ArrayPool<T> Shared(int blockSize)
+		{
+			//lock (_lock)
+			{
+				if (!_pools.TryGetValue(blockSize, out ArrayPool<T>? pool))
+				{
+					pool = new OneSizeArrayPool<T>(blockSize, 100);
+					pool = _pools.TryAdd(blockSize, pool) ? pool : _pools[blockSize];
+				}
+
+				return pool;
+			}
+
+			//_lock.Wait();
+			//try
+			//{
+			//}
+			//finally
+			//{
+			//	_lock.Release();
+			//}
+		}
+	}
+}