azure-sdk-for-net: [BUG] Service Bus - OperationCanceledException in exception received handler while closing the message receiver

Describe the bug I have a QueueClient for receiving messages (basically using it just as MessageReceiver). It is working as expected - the messages are being processed. When I want to stop receiving messages, I call QueueClient.CloseAsync(). There are still messages in the queue, so I will stop the receiver in the middle of the work. So the receiver/client is in the closing state, and I (almost) alway get an error in my ExceptionReceivedHandler - it is OperationCanceledException with the simple message “The operation was canceled.”.

Exception or Stack Trace I do not have a direct exception. Just the exception from ExceptionReceivedEventArgs. The call stack in the received exception is:

at System.Threading.CancellationToken.ThrowOperationCanceledException()
at System.Threading.SemaphoreSlim.WaitUntilCountOrTimeoutAsync(TaskNode asyncWaiter, Int32 millisecondsTimeout, CancellationToken cancellationToken)
at Microsoft.Azure.ServiceBus.MessageReceivePump.MessagePumpTaskAsync()

To Reproduce Just stop MessageReceiver while there still are messages in the queue to process and look in your exception handler.

Expected behavior I am not really sure about it. But I think that if the client is in closing state, I should not get this type of error in my error handler (ExceptionReceivedHandler). It is just annoying, because basically, I will get this error every time I am stopping my receiver.

Setup (please complete the following information):

• OS: Windows 10
• IDE : Visual Studio 2019
• Version of the Library used: Microsoft.Azure.ServiceBus 3.4.0

Additional context I attached the source of Microsoft.Azure.ServiceBus to dig deeper what is going on.

• The system throws while trying to get semaphore lock. The receiver is in closing state: pumpCancellationToken.IsCancellationRequested == true. So the semaphore throws OperationCanceledException.
• In the catch block, there is info about not propagating ObjectDisposedException when the pump is stopping.
• I think, that this situation with OperationCanceledException is the same and it should not be reported too.
• The final note is, that it later comes into the finally block. The condition message == null is true, because loading of the message was skipped. And so it enters the if and releases semaphore lock. I am not sure about this, but I think the lock was not taken (semaphore threw exception), so probably it should not be released.

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