Start Service Bus Client from BackgroundService - .net-core

Question

I have a ServiceBusClient class that creates a QueueClient which is used to listen for messages on a bus. I have looked at the following articles to set this up:
Background tasks (Microsoft)
Hosted services (Microsoft)
Async and Await
My ServiceBusClient class that handles the QueueClient looks like this:
public class ServiceBusClient : IServiceBusClient
{
public ServiceBusClient(IEventService eventService, ServiceBusClientOptions options)
{
...
queueClient = new QueueClient(options.ConnectionString, options.QueueName);
}
public void Run()
{
RegisterOnMessageHandler();
}
private void RegisterOnMessageHandler()
{
...
queueClient.RegisterMessageHandler(ProcessMessagesAsync, messageHandlerOptions);
}
private async Task ProcessMessagesAsync(Message message, CancellationToken token)
{
var eventMessage = EventMessage.FromMessage(message);
await eventService.Write(eventMessage);
if (!token.IsCancellationRequested)
{
await queueClient.CompleteAsync(message.SystemProperties.LockToken);
}
}
private Task ExceptionReceivedHandler(ExceptionReceivedEventArgs exceptionReceivedEventArgs)
{
// log errors
...
return Task.CompletedTask;
}
}
I was hoping to launch from an IHostedService or even by extending the BackgroundService. In the examples I find, work is constantly being executed in a while loop which does not fit my scenario since I am only trying to run a single command.
So I created a super simple implementation like this:
protected override async Task ExecuteAsync(CancellationToken cancellationToken)
{
serviceBusClient.Run();
while (!cancellationToken.IsCancellationRequested)
{
// empty loop to keep running for lifetime of pod
}
}
If removing the async I obviously need to return something. I tried Task.CompletedTask but that required me to change the return type to Task<Task>.
If I have the async in place, I will need to await something, but I am not sure what.
This does not feel right. I would assume I would need to change something in the ServiceBusClient, but I am unsure what, since the ProcessMessagesAsync is async and does the heavy lifting in the background from my understanding.
All I want is for my web app to start listening for messages until it dies. How can I do that?

Answer 1

I gave up on using BackgroundService and implemented IHostedService instead.
public class MessageListenerService : IHostedService
{
private readonly IServiceBusClient client;
private readonly ITelemetryClient applicationInsights;
public MessageListenerService(IServiceProvider serviceProvider)
{
client = serviceProvider.GetService<IServiceBusClient>();
applicationInsights = serviceProvider.GetService<ITelemetryClient>();
}
public Task StartAsync(CancellationToken cancellationToken)
{
applicationInsights.TrackTrace(new TraceTelemetry("MessageListenerService is starting"));
client.Run();
return Task.CompletedTask;
}
public Task StopAsync(CancellationToken cancellationToken)
{
applicationInsights.TrackTrace(new TraceTelemetry("MessageListenerService is stopping"));
return client.Stop();
}
}
If you find issues with this code please let me know in the comments and I'll update as appropriate.
In the end we created a console app for it anyway.