defer awaiting connection reset

Author: caleblloyd

src/MySqlConnector/MySqlClient/ConnectionPool.cs

@@ -26,16 +26,14 @@ public async Task<MySqlSession> GetSessionAsync(IOBehavior ioBehavior, Cancellat
 				// check for a pooled session
 				if (m_sessions.TryDequeue(out session))
 				{
-					if (session.PoolGeneration != m_generation || !await session.TryPingAsync(ioBehavior, cancellationToken).ConfigureAwait(false))
-					{
-						// session is either old or cannot communicate with the server
-						await session.DisposeAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
-					}
-					else
+					if (session.PoolGeneration == m_generation && await session.MakeActiveAsync(ioBehavior, cancellationToken).ConfigureAwait(false))
 					{
 						// pooled session is ready to be used; return it
 						return session;
 					}
+
+					// session is either old, failed to reset connection (if enabled), or cannot communicate with the server
+					await session.DisposeAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 				}
 
 				session = new MySqlSession(this, m_generation);
@@ -51,28 +49,18 @@ public async Task<MySqlSession> GetSessionAsync(IOBehavior ioBehavior, Cancellat
 
 		public void Return(MySqlSession session)
 		{
+			// IO in this method MUST be synchronous, since it is triggered by MySqlConnection.Dispose.  Async IO will cause lock-ups
 			try
 			{
-				var success = false;
-
 				if (session.PoolGeneration == m_generation)
 				{
-					try
-					{
-						// reset the connection upon returning it to the pool
-						if (m_connectionSettings.ConnectionReset)
-							session.ResetConnectionAsync(m_connectionSettings, IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
-						success = true;
-					}
-					catch (MySqlException)
-					{
-					}
-				}
-
-				if (success)
+					session.MakeIdle(m_connectionSettings, IOBehavior.Synchronous, CancellationToken.None);
 					m_sessions.Enqueue(session);
+				}
 				else
+				{
 					session.DisposeAsync(IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
+				}
 			}
 			finally
 			{

src/MySqlConnector/Serialization/MySqlSession.cs

@@ -107,7 +107,30 @@ public async Task ConnectAsync(ConnectionSettings cs, IOBehavior ioBehavior, Can
 				m_payloadHandler = new CompressedPayloadHandler(m_payloadHandler.ByteHandler);
 		}
 
-		public async Task ResetConnectionAsync(ConnectionSettings cs, IOBehavior ioBehavior, CancellationToken cancellationToken)
+		public void MakeIdle(ConnectionSettings cs, IOBehavior ioBehavior, CancellationToken cancellationToken)
+		{
+			if (cs.ConnectionReset)
+				m_resetConnectionTask = ResetConnectionAsync(cs, ioBehavior, cancellationToken);
+		}
+
+		public async Task<bool> MakeActiveAsync(IOBehavior ioBehavior, CancellationToken cancellationToken)
+		{
+			if (m_resetConnectionTask != null)
+			{
+				try
+				{
+					await m_resetConnectionTask.ConfigureAwait(false);
+				}
+				catch (MySqlException)
+				{
+					return false;
+				}
+			}
+
+			return await TryPingAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
+		}
+
+		private async Task ResetConnectionAsync(ConnectionSettings cs, IOBehavior ioBehavior, CancellationToken cancellationToken)
 		{
 			if (ServerVersion.Version.CompareTo(ServerVersions.SupportsResetConnection) >= 0)
 			{
@@ -143,7 +166,7 @@ public async Task ResetConnectionAsync(ConnectionSettings cs, IOBehavior ioBehav
 			}
 		}
 
-		public async Task<bool> TryPingAsync(IOBehavior ioBehavior, CancellationToken cancellationToken)
+		private async Task<bool> TryPingAsync(IOBehavior ioBehavior, CancellationToken cancellationToken)
 		{
 			// check if client socket is still connected
 			// http://stackoverflow.com/questions/2661764/how-to-check-if-a-socket-is-connected-disconnected-in-c
@@ -510,5 +533,6 @@ private enum State
 		Socket m_socket;
 		NetworkStream m_networkStream;
 		IPayloadHandler m_payloadHandler;
+		Task m_resetConnectionTask;
 	}
 }