RecyclableList.IndexOf parallel performance improvements.

Recyclable.Collections/Parallel/BarrierSlimmer.cs

@@ -0,0 +1,117 @@
+using Microsoft.Extensions.ObjectPool;
+using System.Runtime.CompilerServices;
+
+namespace Recyclable.Collections.Parallel
+{
+    public sealed class BarrierSlimmer : IDisposable
+	{
+		private static readonly ObjectPool<BarrierSlimmer> _defaultPool = new DefaultObjectPool<BarrierSlimmer>(new DefaultPooledObjectPolicy<BarrierSlimmer>());
+		private ObjectPool<BarrierSlimmer>? _assignedPool;
+		private readonly SpinLock _lock = new(false);
+
+		public bool HasParticipants;
+		public int Participants;
+
+		[MethodImpl(MethodImplOptions.NoInlining)]
+		public void AddParticipant()
+		{
+			bool isLocked = false;
+			_lock.Enter(ref isLocked);
+
+			Participants++;
+			if (Participants == 1)
+			{
+				HasParticipants = true;
+			}
+
+			if (isLocked)
+			{
+				_lock.Exit(false);
+			}
+		}
+
+		[MethodImpl(MethodImplOptions.NoInlining)]
+		public void RemoveParticipant()
+		{
+			if (!HasParticipants)
+			{
+				ThrowNoMoreParticipants();
+			}
+
+			bool isLocked = false;
+			_lock.Enter(ref isLocked);
+
+			Participants--;
+			if (Participants == 0)
+			{
+				HasParticipants = false;
+			}
+
+			if (isLocked)
+			{
+				_lock.Exit(false);
+			}
+		}
+
+		private static void ThrowNoMoreParticipants()
+		{
+			throw new InvalidOperationException("There are no more participants. The operation is not allowed");
+		}
+
+		public BarrierSlimmer()
+		{
+			_lock = new(false);
+		}
+
+		public BarrierSlimmer(int participants)
+		{
+			_lock = new(false);
+			Participants = participants;
+			HasParticipants = participants > 0;
+		}
+
+		public static BarrierSlimmer Create(int participants)
+		{
+			var result = _defaultPool.Get();
+			result.Participants = participants;
+			result.HasParticipants = participants > 0;
+			return result;
+		}
+
+		public void Dispose()
+		{
+			var assignedPool = _assignedPool;
+			_assignedPool = null;
+			assignedPool?.Return(this);
+
+			GC.SuppressFinalize(this);
+		}
+
+		public void SignalAndWait()
+		{
+			RemoveParticipant();
+
+			//if (!HasParticipants)
+			//{
+			//	return;
+			//}
+
+			//if (!HasParticipants)
+			//{
+			//	return;
+			//}
+
+			//if (!HasParticipants)
+			//{
+			//	return;
+			//}
+
+			// SpinWait.SpinUntil(() => HasParticipants);
+			var waitSpinner = new SpinWait();
+			while (HasParticipants)
+			{
+				waitSpinner.SpinOnce(0);
+			}
+		}
+	}
+}