Is this a bug report?

Yes. Looks like a recurrence of #747 's first issue.

Can you also reproduce the problem with the latest version?

We experienced the problem in 5.1.0. We have deployed 5.1.2 and are waiting to see if the problem occurs again.

Environment

• .NET 4.7.1
• Console EXEs and ASP.NET MVC web app on IIS
• Built with Visual Studio 2017 15.7.2
• Running on Azure App Service x64
• MassTransit using Azure Service Bus
• 3 processes connected to bus
• Each process receives some broadcast messages via per-process queues
• One process receives competing-consumer messages via a shared queue

Steps to Reproduce

Wait until problem occurs. No specific trigger is known.

Expected Behavior

MassTransit remains connected to Azure Service Bus indefinitely.

Actual Behavior

An exception from a Task is unobserved and rethrown from the finalizer thread. Afterward, MassTransit disconnects from Azure Service Bus and receives no more messages until the process is restarted. This occurs around the same time (within 1hr 30min) for all 3 of our processes connected to the bus.

Reproducible Demo

Would love to have one myself.

Stack Trace

System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread.
System.InvalidOperationException: The method 'OnMessage' or 'OnMessageAsync' has already been called.
   at Microsoft.ServiceBus.Messaging.MessageReceiver.OnMessage (Microsoft.ServiceBus, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at Microsoft.ServiceBus.Messaging.QueueClient.OnMessageAsync (Microsoft.ServiceBus, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at MassTransit.AzureServiceBusTransport.Transport.Receiver.Start (MassTransit.AzureServiceBusTransport, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)
   at MassTransit.AzureServiceBusTransport.Pipeline.MessageReceiverFilter+<GreenPipes-IFilter<MassTransit-AzureServiceBusTransport-ClientContext>-Send>d__7.MoveNext (MassTransit.AzureServiceBusTransport, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)
   at GreenPipes.Agents.PipeContextSupervisor`1+<GreenPipes-IPipeContextSource<TContext>-Send>d__8.MoveNext (GreenPipes, Version=2.1.0.106, Culture=neutral, PublicKeyToken=b800c4cfcdeea87b)
   at GreenPipes.Agents.PipeContextSupervisor`1+<GreenPipes-IPipeContextSource<TContext>-Send>d__8.MoveNext (GreenPipes, Version=2.1.0.106, Culture=neutral, PublicKeyToken=b800c4cfcdeea87b)
   at GreenPipes.Agents.PipeContextSupervisor`1+<GreenPipes-IPipeContextSource<TContext>-Send>d__8.MoveNext (GreenPipes, Version=2.1.0.106, Culture=neutral, PublicKeyToken=b800c4cfcdeea87b)
   at MassTransit.AzureServiceBusTransport.Transport.ReceiveTransport+<>c__DisplayClass16_0+<<Receiver>b__0>d.MoveNext (MassTransit.AzureServiceBusTransport, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)
   at MassTransit.AzureServiceBusTransport.Transport.ReceiveTransport+<>c__DisplayClass16_0+<<Receiver>b__0>d.MoveNext (MassTransit.AzureServiceBusTransport, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)
   at MassTransit.Policies.PipeRetryExtensions+<Retry>d__1.MoveNext (MassTransit, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)
   at MassTransit.Policies.PipeRetryExtensions+<Retry>d__1.MoveNext (MassTransit, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)
   at MassTransit.AzureServiceBusTransport.Transport.ReceiveTransport+<Receiver>d__16.MoveNext (MassTransit.AzureServiceBusTransport, Version=5.1.0.1516, Culture=neutral, PublicKeyToken=b8e0e9f2f1e657fa)

Bus Configuration

private IBusControl CreateBusUsingAzureServiceBus()
{
    return Bus.Factory.CreateUsingAzureServiceBus(c =>
    {
        // Normalize the URI
        var uri = Configuration.HostUri;
            uri = ServiceBusEnvironment.CreateServiceUri(AzureServiceBusScheme, uri.Host, "");

        // Configure connection to Azure Service Bus
        var host = c.Host(uri, h =>
        {
            h.SharedAccessSignature(s =>
            {
                s.KeyName         = Configuration.Secret?.UserName;
                s.SharedAccessKey = Configuration.Secret?.Password;
                s.TokenTimeToLive = TimeSpan.FromDays(1);
                s.TokenScope      = TokenScope.Namespace;
            });
        });

        // Disable retries by default
        c.UseRetry(a => a.None());

        // Everything below is for message reception
        if (!Configuration.IsReceiveEnabled)
            return;

        // Ensure long-running consumers will not lose their lock on the message
        c.UseRenewLock();

        // Configure the request queue (shared among all instances, persistent)
        c.ReceiveEndpoint(host, Configuration.QueueName, r =>
        {
            ConfigureFilters(r);
            LoadRequestConsumers(r);
        });

        // Configure the event queue (per-instance, auto-deleted)
        c.ReceiveEndpoint(host, r =>
        {
            // NOTE: Though the queue will auto-delete after 5 min, the
            // subcriptions for it will remain, and worse, will fill up
            // with messages. An external maintenance script should run
            // periodically to clean up those go-nowhere subscriptions.
            // Source: https://github.com/MassTransit/MassTransit/issues/553
            ConfigureFilters(r);
            LoadEventConsumers(r);
        });

        // If the normal plumbing fails, MassTransit will move messages
        // to an error queue.  We currently do not monitor the error
        // queue, so we just need to prevent it from filling up.
        c.ReceiveEndpoint(host, Configuration.QueueName + "_error", r =>
        {
            // Log any request in the error queue
            r.Consumer<LoggingConsumer>();
        });
    });
}

private static void ConfigureFilters(IPipeConfigurator<ConsumeContext> c)
{
    c.UseFilter(new LoggingFilter            <ConsumeContext>());
    c.UseFilter(new ApplicationInsightsFilter<ConsumeContext>());
}

protected virtual void LoadRequestConsumers(IReceiveEndpointConfigurator r)
{
    // Messages that use competing-consumer
    r.LoadConsumersFrom(_context, IsRequestMessage);
}

protected virtual void LoadEventConsumers(IReceiveEndpointConfigurator r)
{
    // Messages that are broadcast
    r.LoadConsumersFrom(_context, IsEventMessage);
}