azure-sdk-for-net: Service Bus subscriber stops processing messages

Describe the bug After 5000 messages are processed by the subscriber, the subscriber doesn’t accept any more messages. No exception are thrown by the subscriber.

Async message delegate doesn’t receive any more messages. Any sync/async operation locks indefinitely.

Exception or Stack Trace No exception are thrown.

To Reproduce Execute snippet below

Code Snippet

static readonly ConcurrentBag<Tuple<string, string>> messageRefs = new ConcurrentBag<Tuple<string, string>>();

        static void Main(string[] args)
        {
            /*
                * Subscription Details
                * Max delivery count: 10
                * Lock Duration: 2minutes
            */

            var receiver = CreateSubscriptionClient();
            var options = new MessageHandlerOptions(ExceptionReceivedHandler)
            {
                MaxConcurrentCalls = 5,
                AutoComplete = false,
            };

            receiver.RegisterMessageHandler(async (message, cancellation) =>
            {
                try
                {
                    messageRefs.Add(new Tuple<string, string>(message.MessageId.ToString(), message.SystemProperties.LockToken));

                    throw new Exception("something bad happens...");
                    await receiver.CompleteAsync(message.SystemProperties.LockToken);
                }
                catch (Exception)
                {
                    //we do not want to return the message immediately (receiver.AbandonAsync)
                    //let the message lock (2min) expire before this message being re-processed
                }
            }, options);

            while (true) //monitor
            {
                Console.WriteLine($"Message read: {messageRefs.Count}");
                if (MONITOR_VERBOSE)
                    Console.WriteLine(
                        String.Join(
                            Environment.NewLine,
                            messageRefs
                                .GroupBy(x => x.Item1)
                                .OrderByDescending(x => x.Count())
                                .Take(10)
                                .Select(x => $"Id: {x.Key} | Locks: {x.Count()}")));
                Thread.Sleep(5000);
            }
        }

Expected behavior

We are aware of the max 5000 concurrent connections to subscriber entities while using the amqp protocol. We are although expecting those connections to be released, when the message lock expires.

Specifically, we want the lock (30secs) to expire before the message being visible again. As indeed highlighted from the previous snippet, after the lock expires, the message is picked up again by the same subscriber, but the previous connection is not released, bringing the subscriber into a locked state

Additional context Same behavior from WindowsAzure.ServiceBus library.

Setup (please complete the following information):

• OS: Win10
• 3.4.0