Handle race condition in OpenTcpSocketAsync. Fixes #476

Author: bgrainger

src/MySqlConnector/Core/ServerSession.cs

@@ -694,7 +694,7 @@ private async Task<bool> OpenTcpSocketAsync(ConnectionSettings cs, ILoadBalancer
 					{
 						tcpClient = new TcpClient(ipAddress.AddressFamily);
 
-						using (cancellationToken.Register(() => tcpClient?.Client?.Dispose()))
+						using (cancellationToken.Register(() => tcpClient.Client?.Dispose()))
 						{
 							try
 							{
@@ -727,17 +727,25 @@ private async Task<bool> OpenTcpSocketAsync(ConnectionSettings cs, ILoadBalancer
 							}
 							catch (ObjectDisposedException ex) when (cancellationToken.IsCancellationRequested)
 							{
+								SafeDispose(ref tcpClient);
 								Log.Info("Session{0} connect timeout expired connecting to IpAddress {1} for HostName '{2}'", m_logArguments[0], ipAddress, hostName);
 								throw new MySqlException("Connect Timeout expired.", ex);
 							}
 						}
 					}
 					catch (SocketException)
 					{
-						tcpClient?.Client?.Dispose();
+						SafeDispose(ref tcpClient);
 						continue;
 					}
 
+					if (!tcpClient.Connected && cancellationToken.IsCancellationRequested)
+					{
+						SafeDispose(ref tcpClient);
+						Log.Info("Session{0} connect timeout expired connecting to IpAddress {1} for HostName '{2}'", m_logArguments[0], ipAddress, hostName);
+						throw new MySqlException("Connect Timeout expired.");
+					}
+
 					HostName = hostName;
 					m_tcpClient = tcpClient;
 					m_socket = m_tcpClient.Client;