Perf: add allocation free path for close notifications

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlCommand.cs

@@ -2550,7 +2550,10 @@ private Task<int> InternalExecuteNonQueryAsync(CancellationToken cancellationTok
             SqlClientEventSource.Log.TryCorrelationTraceEvent("SqlCommand.InternalExecuteNonQueryAsync | API | Correlation | Object Id {0}, Activity Id {1}, Client Connection Id {2}, Command Text '{3}'", ObjectID, ActivityCorrelator.Current, Connection?.ClientConnectionId, CommandText);
             Guid operationId = s_diagnosticListener.WriteCommandBefore(this, _transaction);
 
-            TaskCompletionSource<int> source = new TaskCompletionSource<int>();
+            // connection can be used as state in RegisterForConnectionCloseNotification continuation
+            // to avoid an allocation so use it as the state value if possible but it can be changed if
+            // you need it for a more important piece of data that justifies the tuple allocation later
+            TaskCompletionSource<int> source = new TaskCompletionSource<int>(_activeConnection);
 
             CancellationTokenRegistration registration = new CancellationTokenRegistration();
             if (cancellationToken.CanBeCanceled)
@@ -2674,7 +2677,10 @@ private Task<SqlDataReader> InternalExecuteReaderAsync(CommandBehavior behavior,
                 operationId = s_diagnosticListener.WriteCommandBefore(this, _transaction);
             }
 
-            TaskCompletionSource<SqlDataReader> source = new TaskCompletionSource<SqlDataReader>();
+            // connection can be used as state in RegisterForConnectionCloseNotification continuation
+            // to avoid an allocation so use it as the state value if possible but it can be changed if
+            // you need it for a more important piece of data that justifies the tuple allocation later
+            TaskCompletionSource<SqlDataReader> source = new TaskCompletionSource<SqlDataReader>(_activeConnection);
 
             CancellationTokenRegistration registration = new CancellationTokenRegistration();
             if (cancellationToken.CanBeCanceled)
@@ -2846,7 +2852,10 @@ private Task<XmlReader> InternalExecuteXmlReaderAsync(CancellationToken cancella
             SqlClientEventSource.Log.TryCorrelationTraceEvent("SqlCommand.InternalExecuteXmlReaderAsync | API | Correlation | Object Id {0}, Activity Id {1}, Client Connection Id {2}, Command Text '{3}'", ObjectID, ActivityCorrelator.Current, Connection?.ClientConnectionId, CommandText);
             Guid operationId = s_diagnosticListener.WriteCommandBefore(this, _transaction);
 
-            TaskCompletionSource<XmlReader> source = new TaskCompletionSource<XmlReader>();
+            // connection can be used as state in RegisterForConnectionCloseNotification continuation
+            // to avoid an allocation so use it as the state value if possible but it can be changed if
+            // you need it for a more important piece of data that justifies the tuple allocation later
+            TaskCompletionSource<XmlReader> source = new TaskCompletionSource<XmlReader>(_activeConnection);
 
             CancellationTokenRegistration registration = new CancellationTokenRegistration();
             if (cancellationToken.CanBeCanceled)

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

@@ -2231,17 +2231,44 @@ private static void ChangePassword(string connectionString, SqlConnectionString
         internal Task<T> RegisterForConnectionCloseNotification<T>(Task<T> outerTask, object value, int tag)
         {
             // Connection exists,  schedule removal, will be added to ref collection after calling ValidateAndReconnect
+
+            object state = null;
+            if (outerTask.AsyncState == this)
+            {
+                // if the caller created the TaskCompletionSource for outerTask with this connection
+                // as the state parameter (which is immutable) we can use task.AsyncState and state
+                // to carry the two pieces of state that we need into the continuation avoiding the
+                // allocation of a new state object to carry them
+                state = value;
+            }
+            else
+            {
+                // otherwise we need to create a Tuple to carry the two pieces of state
+                state = Tuple.Create(this, value);
+            }
+
             return outerTask.ContinueWith(
                 continuationFunction: static (task, state) =>
                 {
-                    Tuple<SqlConnection, object> parameters = (Tuple<SqlConnection, object>)state;
-                    SqlConnection connection = parameters.Item1;
-                    object obj = parameters.Item2;
+                    SqlConnection connection = null;
+                    object obj = null;
+                    if (state is Tuple<SqlConnection, object> tuple)
+                    {
+                        // special state tuple, unpack it
+                        connection = tuple.Item1;
+                        obj = tuple.Item2;
+                    }
+                    else
+                    {
+                        // use state on task and state object
+                        connection = (SqlConnection)task.AsyncState;
+                        obj = state;
+                    }
 
                     connection.RemoveWeakReference(obj);
                     return task;
                 },
-                state: Tuple.Create(this, value),
+                state: state,
                 scheduler: TaskScheduler.Default
            ).Unwrap();
         }

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

@@ -2310,7 +2310,7 @@ private Task ReadWriteColumnValueAsync(int col)
             return writeTask;
         }
 
-        private void RegisterForConnectionCloseNotification<T>(ref Task<T> outterTask)
+        private Task<T> RegisterForConnectionCloseNotification<T>(Task<T> outterTask)
         {
             SqlConnection connection = _connection;
             if (connection == null)
@@ -2319,7 +2319,7 @@ private void RegisterForConnectionCloseNotification<T>(ref Task<T> outterTask)
                 throw ADP.ClosedConnectionError();
             }
 
-            connection.RegisterForConnectionCloseNotification<T>(ref outterTask, this, SqlReferenceCollection.BulkCopyTag);
+            return connection.RegisterForConnectionCloseNotification(outterTask, this, SqlReferenceCollection.BulkCopyTag);
         }
 
         // Runs a loop to copy all columns of a single row.
@@ -3139,9 +3139,7 @@ private Task WriteToServerInternalAsync(CancellationToken ctoken)
             if (_isAsyncBulkCopy)
             {
                 source = new TaskCompletionSource<object>(); // Creating the completion source/Task that we pass to application
-                resultTask = source.Task;
-
-                RegisterForConnectionCloseNotification(ref resultTask);
+                resultTask = RegisterForConnectionCloseNotification(source.Task);
             }
 
             if (_destinationTableName == null)

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

@@ -2964,7 +2964,10 @@ private Task<int> InternalExecuteNonQueryAsync(CancellationToken cancellationTok
             SqlClientEventSource.Log.TryCorrelationTraceEvent("<sc.SqlCommand.ExecuteNonQueryAsync|API|Correlation> ObjectID {0}, ActivityID {1}", ObjectID, ActivityCorrelator.Current);
             SqlConnection.ExecutePermission.Demand();
 
-            TaskCompletionSource<int> source = new TaskCompletionSource<int>();
+            // connection can be used as state in RegisterForConnectionCloseNotification continuation
+            // to avoid an allocation so use it as the state value if possible but it can be changed if
+            // you need it for a more important piece of data that justifies the tuple allocation later
+            TaskCompletionSource<int> source = new TaskCompletionSource<int>(_activeConnection);
 
             CancellationTokenRegistration registration = new CancellationTokenRegistration();
             if (cancellationToken.CanBeCanceled)
@@ -2980,7 +2983,7 @@ private Task<int> InternalExecuteNonQueryAsync(CancellationToken cancellationTok
             Task<int> returnedTask = source.Task;
             try
             {
-                RegisterForConnectionCloseNotification(ref returnedTask);
+                returnedTask = RegisterForConnectionCloseNotification(returnedTask);
 
                 Task<int>.Factory.FromAsync(BeginExecuteNonQueryAsync, EndExecuteNonQueryAsync, null).ContinueWith((t) =>
                 {
@@ -3061,7 +3064,10 @@ private Task<SqlDataReader> InternalExecuteReaderAsync(CommandBehavior behavior,
             SqlClientEventSource.Log.TryCorrelationTraceEvent("<sc.SqlCommand.ExecuteReaderAsync|API|Correlation> ObjectID {0}, behavior={1}, ActivityID {2}", ObjectID, (int)behavior, ActivityCorrelator.Current);
             SqlConnection.ExecutePermission.Demand();
 
-            TaskCompletionSource<SqlDataReader> source = new TaskCompletionSource<SqlDataReader>();
+            // connection can be used as state in RegisterForConnectionCloseNotification continuation
+            // to avoid an allocation so use it as the state value if possible but it can be changed if
+            // you need it for a more important piece of data that justifies the tuple allocation later
+            TaskCompletionSource<SqlDataReader> source = new TaskCompletionSource<SqlDataReader>(_activeConnection);
 
             CancellationTokenRegistration registration = new CancellationTokenRegistration();
             if (cancellationToken.CanBeCanceled)
@@ -3077,7 +3083,7 @@ private Task<SqlDataReader> InternalExecuteReaderAsync(CommandBehavior behavior,
             Task<SqlDataReader> returnedTask = source.Task;
             try
             {
-                RegisterForConnectionCloseNotification(ref returnedTask);
+                returnedTask = RegisterForConnectionCloseNotification(returnedTask);
 
                 Task<SqlDataReader>.Factory.FromAsync(BeginExecuteReaderAsync, EndExecuteReaderAsync, behavior, null).ContinueWith((t) =>
                 {
@@ -3207,7 +3213,10 @@ private Task<XmlReader> InternalExecuteXmlReaderAsync(CancellationToken cancella
             SqlClientEventSource.Log.TryCorrelationTraceEvent("<sc.SqlCommand.ExecuteXmlReaderAsync|API|Correlation> ObjectID {0}, ActivityID {1}", ObjectID, ActivityCorrelator.Current);
             SqlConnection.ExecutePermission.Demand();
 
-            TaskCompletionSource<XmlReader> source = new TaskCompletionSource<XmlReader>();
+            // connection can be used as state in RegisterForConnectionCloseNotification continuation
+            // to avoid an allocation so use it as the state value if possible but it can be changed if
+            // you need it for a more important piece of data that justifies the tuple allocation later
+            TaskCompletionSource<XmlReader> source = new TaskCompletionSource<XmlReader>(_activeConnection);
 
             CancellationTokenRegistration registration = new CancellationTokenRegistration();
             if (cancellationToken.CanBeCanceled)
@@ -3223,7 +3232,7 @@ private Task<XmlReader> InternalExecuteXmlReaderAsync(CancellationToken cancella
             Task<XmlReader> returnedTask = source.Task;
             try
             {
-                RegisterForConnectionCloseNotification(ref returnedTask);
+                returnedTask = RegisterForConnectionCloseNotification(returnedTask);
 
                 Task<XmlReader>.Factory.FromAsync(BeginExecuteXmlReaderAsync, EndExecuteXmlReaderAsync, null).ContinueWith((t) =>
                 {
@@ -5814,7 +5823,7 @@ object ICloneable.Clone()
             return Clone();
         }
 
-        private void RegisterForConnectionCloseNotification<T>(ref Task<T> outterTask)
+        private Task<T> RegisterForConnectionCloseNotification<T>(Task<T> outterTask)
         {
             SqlConnection connection = _activeConnection;
             if (connection == null)
@@ -5823,7 +5832,7 @@ private void RegisterForConnectionCloseNotification<T>(ref Task<T> outterTask)
                 throw ADP.ClosedConnectionError();
             }
 
-            connection.RegisterForConnectionCloseNotification<T>(ref outterTask, this, SqlReferenceCollection.CommandTag);
+            return connection.RegisterForConnectionCloseNotification(outterTask, this, SqlReferenceCollection.CommandTag);
         }
 
         // validates that a command has commandText and a non-busy open connection

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

@@ -2805,16 +2805,52 @@ private static void ChangePassword(string connectionString, SqlConnectionString
             SqlConnectionFactory.SingletonInstance.ClearPool(key);
         }
 
-        internal void RegisterForConnectionCloseNotification<T>(ref Task<T> outerTask, object value, int tag)
+        internal Task<T> RegisterForConnectionCloseNotification<T>(Task<T> outerTask, object value, int tag)
         {
             // Connection exists,  schedule removal, will be added to ref collection after calling ValidateAndReconnect
-            outerTask = outerTask.ContinueWith(task =>
+
+            object state = null;
+            if (outerTask.AsyncState == this)
+            {
+                // if the caller created the TaskCompletionSource for outerTask with this connection
+                // as the state parameter (which is immutable) we can use task.AsyncState and state
+                // to carry the two pieces of state that we need into the continuation avoiding the
+                // allocation of a new state object to carry them
+                state = value;
+            }
+            else
             {
-                RemoveWeakReference(value);
-                return task;
-            }, TaskScheduler.Default).Unwrap();
+                // otherwise we need to create a Tuple to carry the two pieces of state
+                state = Tuple.Create(this, value);
+            }
+
+            return outerTask.ContinueWith(
+                continuationFunction: static (task, state) =>
+                {
+                    SqlConnection connection = null;
+                    object obj = null;
+                    if (state is Tuple<SqlConnection, object> tuple)
+                    {
+                        // special state tuple, unpack it
+                        connection = tuple.Item1;
+                        obj = tuple.Item2;
+                    }
+                    else
+                    {
+                        // use state on task and state object
+                        connection = (SqlConnection)task.AsyncState;
+                        obj = state;
+                    }
+
+                    connection.RemoveWeakReference(obj);
+                    return task;
+                },
+                state: state,
+                scheduler: TaskScheduler.Default
+           ).Unwrap();
         }
 
+
         // updates our context with any changes made to the memory-mapped data by an external process
         static private void RefreshMemoryMappedData(SqlDebugContext sdc)
         {