CSHARP-1375: Fix race conditions while connecting a socket.

Author: rstam

src/MongoDB.Driver.Core/Core/Connections/TcpStreamFactory.cs

@@ -74,11 +74,12 @@ private void ConfigureConnectedSocket(Socket socket)
 
         private void Connect(Socket socket, EndPoint endPoint, CancellationToken cancellationToken)
         {
+            var connected = false;
             var cancelled = false;
             var timedOut = false;
 
-            using (var registration = cancellationToken.Register(() => { cancelled = true; try { socket.Close(); } catch { } }))
-            using (var timer = new Timer(_ => { timedOut = true; try { socket.Close(); } catch { } }, null, _settings.ConnectTimeout, Timeout.InfiniteTimeSpan))
+            using (var registration = cancellationToken.Register(() => { if (!connected) { cancelled = true; try { socket.Close(); } catch { } } }))
+            using (var timer = new Timer(_ => { if (!connected) { timedOut = true; try { socket.Close(); } catch { } } }, null, _settings.ConnectTimeout, Timeout.InfiniteTimeSpan))
             {
                 try
                 {
@@ -92,6 +93,8 @@ private void Connect(Socket socket, EndPoint endPoint, CancellationToken cancell
                     {
                         socket.Connect(endPoint);
                     }
+                    connected = true;
+                    return;
                 }
                 catch
                 {
@@ -102,6 +105,11 @@ private void Connect(Socket socket, EndPoint endPoint, CancellationToken cancell
                 }
             }
 
+            if (socket.Connected)
+            {
+                try { socket.Close(); } catch { }
+            }
+
             cancellationToken.ThrowIfCancellationRequested();
             if (timedOut)
             {
@@ -112,11 +120,12 @@ private void Connect(Socket socket, EndPoint endPoint, CancellationToken cancell
 
         private async Task ConnectAsync(Socket socket, EndPoint endPoint, CancellationToken cancellationToken)
         {
+            var connected = false;
             var cancelled = false;
             var timedOut = false;
 
-            using (var registration = cancellationToken.Register(() => { cancelled = true; try { socket.Close(); } catch { } }))
-            using (var timer = new Timer(_ => { timedOut = true; try { socket.Close(); } catch { } }, null, _settings.ConnectTimeout, Timeout.InfiniteTimeSpan))
+            using (var registration = cancellationToken.Register(() => { if (!connected) { cancelled = true; try { socket.Close(); } catch { } } }))
+            using (var timer = new Timer(_ => { if (!connected) { timedOut = true; try { socket.Close(); } catch { } } }, null, _settings.ConnectTimeout, Timeout.InfiniteTimeSpan))
             {
                 try
                 {
@@ -130,6 +139,8 @@ private async Task ConnectAsync(Socket socket, EndPoint endPoint, CancellationTo
                     {
                         await Task.Factory.FromAsync(socket.BeginConnect(endPoint, null, null), socket.EndConnect).ConfigureAwait(false);
                     }
+                    connected = true;
+                    return;
                 }
                 catch
                 {
@@ -140,6 +151,11 @@ private async Task ConnectAsync(Socket socket, EndPoint endPoint, CancellationTo
                 }
             }
 
+            if (socket.Connected)
+            {
+                try { socket.Close(); } catch { }
+            }
+
             cancellationToken.ThrowIfCancellationRequested();
             if (timedOut)
             {