Make sure MySqlConnection isn't GCed.

If the MySqlConnection associated with the ServerSession was garbage collected, then the ServerSession could inaccurately be detected as being leaked, even though it's being reset about about to be returned to the pool.

Author: bgrainger

src/MySqlConnector/Core/BackgroundConnectionResetHelper.cs

@@ -9,13 +9,11 @@ namespace MySqlConnector.Core
 {
 	internal static class BackgroundConnectionResetHelper
 	{
-		public static void AddSession(ServerSession session)
+		public static void AddSession(ServerSession session, MySqlConnection? owningConnection)
 		{
-			// TODO: save the MySqlConnection object so this session isn't considered leaked
-
 			var resetTask = session.TryResetConnectionAsync(session.Pool!.ConnectionSettings, IOBehavior.Asynchronous, default);
 			lock (s_lock)
-				s_sessions.Add(new SessionResetTask(session, resetTask));
+				s_sessions.Add(new SessionResetTask(session, resetTask, owningConnection));
 
 			if (Log.IsDebugEnabled())
 				Log.Debug("Started Session{0} reset in background; waiting SessionCount: {1}.", session.Id, s_sessions.Count);
@@ -71,7 +69,7 @@ public static async Task ReturnSessionsAsync()
 			Log.Info("Started BackgroundConnectionResetHelper worker.");
 
 			List<Task<bool>> localTasks = new();
-			List<ServerSession> localSessions = new();
+			List<SessionResetTask> localSessions = new();
 
 			// keep running until stopped
 			while (!s_cancellationTokenSource.IsCancellationRequested)
@@ -94,10 +92,10 @@ public static async Task ReturnSessionsAsync()
 							}
 							else
 							{
-								foreach (var data in s_sessions)
+								foreach (var session in s_sessions)
 								{
-									localSessions.Add(data.Session);
-									localTasks.Add(data.ResetTask);
+									localSessions.Add(session);
+									localTasks.Add(session.ResetTask);
 								}
 								s_sessions.Clear();
 							}
@@ -110,7 +108,7 @@ public static async Task ReturnSessionsAsync()
 						{
 							var completedTask = await Task.WhenAny(localTasks).ConfigureAwait(false);
 							var index = localTasks.IndexOf(completedTask);
-							var session = localSessions[index];
+							var session = localSessions[index].Session;
 							await session.Pool!.ReturnAsync(IOBehavior.Asynchronous, session).ConfigureAwait(false);
 							localSessions.RemoveAt(index);
 							localTasks.RemoveAt(index);
@@ -126,21 +124,23 @@ public static async Task ReturnSessionsAsync()
 
 		internal struct SessionResetTask
 		{
-			public SessionResetTask(ServerSession session, Task<bool> resetTask)
+			public SessionResetTask(ServerSession session, Task<bool> resetTask, MySqlConnection? owningConnection)
 			{
 				Session = session;
 				ResetTask = resetTask;
+				OwningConnection = owningConnection;
 			}
 
 			public ServerSession Session { get; }
 			public Task<bool> ResetTask { get; }
+			public MySqlConnection? OwningConnection { get; }
 		}
 
 		static readonly IMySqlConnectorLogger Log = MySqlConnectorLogManager.CreateLogger(nameof(BackgroundConnectionResetHelper));
 		static readonly object s_lock = new();
 		static readonly SemaphoreSlim s_semaphore = new(1, 1);
 		static readonly CancellationTokenSource s_cancellationTokenSource = new();
-		static List<SessionResetTask> s_sessions = new();
+		static readonly List<SessionResetTask> s_sessions = new();
 		static Task? s_workerTask;
 	}
 }

src/MySqlConnector/Core/ConnectionPool.cs

@@ -249,7 +249,7 @@ private async Task RecoverLeakedSessionsAsync(IOBehavior ioBehavior)
 			else
 				Log.Warn("Pool{0}: RecoveredSessionCount={1}", m_logArguments[0], recoveredSessions.Count);
 			foreach (var session in recoveredSessions)
-				await session.ReturnToPoolAsync(ioBehavior).ConfigureAwait(false);
+				await session.ReturnToPoolAsync(ioBehavior, null).ConfigureAwait(false);
 		}
 
 		private async Task CleanPoolAsync(IOBehavior ioBehavior, Func<ServerSession, bool> shouldCleanFn, bool respectMinPoolSize, CancellationToken cancellationToken)

src/MySqlConnector/Core/ServerSession.cs

@@ -68,7 +68,7 @@ public ServerSession(ConnectionPool? pool, int poolGeneration, int id)
 		public bool SupportsSessionTrack => m_supportsSessionTrack;
 		public bool ProcAccessDenied { get; set; }
 
-		public Task ReturnToPoolAsync(IOBehavior ioBehavior)
+		public Task ReturnToPoolAsync(IOBehavior ioBehavior, MySqlConnection? owningConnection)
 		{
 			if (Log.IsDebugEnabled())
 			{
@@ -80,7 +80,7 @@ public Task ReturnToPoolAsync(IOBehavior ioBehavior)
 				return Utility.CompletedTask;
 			if (!Pool.ConnectionSettings.ConnectionReset || Pool.ConnectionSettings.DeferConnectionReset)
 				return Pool.ReturnAsync(ioBehavior, this);
-			BackgroundConnectionResetHelper.AddSession(this);
+			BackgroundConnectionResetHelper.AddSession(this, owningConnection);
 			return Utility.CompletedTask;
 		}
 

src/MySqlConnector/MySqlConnection.cs

@@ -925,7 +925,7 @@ m_enlistedTransaction is null &&
 				m_cachedProcedures = null;
 				if (m_session is not null)
 				{
-					await m_session.ReturnToPoolAsync(ioBehavior).ConfigureAwait(false);
+					await m_session.ReturnToPoolAsync(ioBehavior, this).ConfigureAwait(false);
 					m_session = null;
 				}
 				if (changeState)
@@ -994,7 +994,7 @@ private async Task DoCloseAsync(bool changeState, IOBehavior ioBehavior)
 				{
 					if (GetInitializedConnectionSettings().Pooling)
 					{
-						await m_session.ReturnToPoolAsync(ioBehavior).ConfigureAwait(false);
+						await m_session.ReturnToPoolAsync(ioBehavior, this).ConfigureAwait(false);
 					}
 					else
 					{