Processor improvements (#26904)

* Use the right overload for the ContinueWith in the receiver manager make sure the continuation is actually using ExecuteSynchronously

* Update change log

* Remove array allocation from linked token source creation

* Update changelog

Author: danielmarbach

sdk/servicebus/Azure.Messaging.ServiceBus/CHANGELOG.md

@@ -8,6 +8,11 @@ Thank you to our developer community members who helped to make the Service Bus
 - Max Hamulyak _([GitHub](https://github.com/kaylumah))_
 - Daniel Marbach  _([GitHub](https://github.com/danielmarbach))_
 
+### Bugs Fixed
+
+- Fix unnecessary task scheduling in ServiceBusProcessor and ServiceBusSessionProcessor
+- Remove array allocation when creating linked token sources from the ServiceBusProcessor
+
 ### Features Added
 
 - The `State` property has been added to `ServiceBusReceivedMessage` which indicates whether a message is `Active`, `Scheduled`, or `Deferred`. _(A community contribution, courtesy of [danielmarbach](https://github.com/danielmarbach))_

sdk/servicebus/Azure.Messaging.ServiceBus/src/Processor/ReceiverManager.cs

@@ -262,7 +262,8 @@ private async Task RenewMessageLock(
                     // by the renewLockCancellationToken. This way we prevent a TaskCanceledException.
                     Task delayTask = await Task.Delay(delay, cancellationToken)
                         .ContinueWith(
-                            (t, s) => t,
+                            t => t,
+                            CancellationToken.None,
                             TaskContinuationOptions.ExecuteSynchronously,
                             TaskScheduler.Default)
                         .ConfigureAwait(false);

sdk/servicebus/Azure.Messaging.ServiceBus/src/Processor/ServiceBusProcessor.cs

@@ -812,7 +812,9 @@ private async Task RunReceiveTaskAsync(CancellationToken cancellationToken)
                         // hold onto all the tasks that we are starting so that when cancellation is requested,
                         // we can await them to make sure we surface any unexpected exceptions, i.e. exceptions
                         // other than TaskCanceledExceptions
-                        var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+                        // Instead of using the array overload which allocates an array, we use the overload that has two parameters
+                        // and pass in CancellationToken.None. This should be safe since CanBeCanceled will return false.
+                        var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, CancellationToken.None);
 
                         TaskTuples.Add(
                             (

sdk/servicebus/Azure.Messaging.ServiceBus/src/Processor/SessionReceiverManager.cs

@@ -350,7 +350,8 @@ private async Task RenewSessionLock()
                     // by the renewLockCancellationToken. This way we prevent a TaskCanceledException.
                     Task delayTask = await Task.Delay(delay, sessionLockRenewalCancellationToken)
                         .ContinueWith(
-                            (t, s) => t,
+                            t => t,
+                            CancellationToken.None,
                             TaskContinuationOptions.ExecuteSynchronously,
                             TaskScheduler.Default)
                         .ConfigureAwait(false);