RecyclableList.IndexOf performance improvements.

Recyclable.Collections/Parallel/IndexOfSynchronizationContext.cs

@@ -1,22 +1,71 @@
 namespace Recyclable.Collections.Parallel
 {
-	public sealed class IndexOfSynchronizationContext : IDisposable
+	public sealed class IndexOfSynchronizationContext
 	{
+		private readonly SpinWait _participantsSpinWait = new();
+
 		internal bool _isItemFound;
+		internal int _participants;
+		internal bool _returned;
+
+		public void AddParticipant()
+		{
+			_ = Interlocked.Increment(ref _participants);
+		}
+
+		public void AddParticipants(int newParticipants)
+		{
+			_ = Interlocked.Add(ref _participants, newParticipants);
+		}
+
+		public void RemoveParticipants(int participantsToRemove)
+		{
+			if (_participants < participantsToRemove)
+			{
+				ThrowNotEnoughParticipants();
+			}
+
+			_ = Interlocked.Add(ref _participants, -participantsToRemove);
+		}
+
+		public void RemoveParticipant()
+		{
+			if (_participants == 0)
+			{
+				ThrowNoMoreParticipants();
+			}
+
+			_ = Interlocked.Decrement(ref _participants);
+		}
+
+		public void SignalAndWait()
+		{
+			if (_participants == 0)
+			{
+				ThrowNoMoreParticipants();
+			}
+
+			_ = Interlocked.Decrement(ref _participants);
+			while (_participants > 0)
+			{
+				_participantsSpinWait.SpinOnce();
+			}
+		}
+
+		private static void ThrowNotEnoughParticipants() => throw new InvalidOperationException("Participant cannot be removed, because there are not enough participants.");
+		private static void ThrowNoMoreParticipants() => throw new InvalidOperationException("Participant cannot be removed, because there are no more participants.");
 
-		public readonly Barrier AllDoneSignal;
 		public long FoundItemIndex;
 		public Exception? Exception;
-		internal bool _returned;
+		public int Participants => _participants;
 
 		public IndexOfSynchronizationContext()
 		{
-			AllDoneSignal = new(0);
 		}
 
 		public IndexOfSynchronizationContext(int participantCount)
 		{
-			AllDoneSignal = new(participantCount);
+			_participants = participantCount;
 		}
 
 		public void SetItemFound()
@@ -33,11 +82,6 @@ namespace Recyclable.Collections.Parallel
 				_returned = true;
 				IndexOfSynchronizationContextPool.Shared.Return(this);
 			}
-			else
-			{
-				AllDoneSignal.Dispose();
-				GC.SuppressFinalize(this);
-			}
 		}
 	}
 }