netfx: port dotnet#378

Author: edwardneal

src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlConnection.cs

@@ -119,6 +119,7 @@ private static readonly ConcurrentDictionary<string, IList<string>> _ColumnEncry
                                                             capacity: 1,
                                                             comparer: StringComparer.OrdinalIgnoreCase);
 
+        private static readonly Action<object> s_openAsyncCancel = OpenAsyncCancel;
         private static readonly Action<Task<object>, object> s_openAsyncComplete = OpenAsyncComplete;
 
         private bool IsProviderRetriable => SqlConfigurableRetryFactory.IsRetriable(RetryLogicProvider);
@@ -1768,7 +1769,7 @@ private Task InternalOpenAsync(SqlConnectionOverrides overrides, CancellationTok
                         CancellationTokenRegistration registration = new CancellationTokenRegistration();
                         if (cancellationToken.CanBeCanceled)
                         {
-                            registration = cancellationToken.Register(() => completion.TrySetCanceled());
+                            registration = cancellationToken.Register(s_openAsyncCancel, completion);
                         }
                         OpenAsyncRetry retry = new OpenAsyncRetry(this, completion, result, overrides, registration);
                         _currentCompletion = new Tuple<TaskCompletionSource<DbConnectionInternal>, Task>(completion, result.Task);
@@ -1810,6 +1811,11 @@ private static void OpenAsyncComplete(Task<object> task, object state)
             }
         }
 
+        private static void OpenAsyncCancel(object state)
+        {
+            ((TaskCompletionSource<DbConnectionInternal>)state).TrySetCanceled();
+        }
+
         private class OpenAsyncRetry
         {
             private SqlConnection _parent;