.Net core Hosted Services guaranteed to complete

Question

I'm looking at .Net-Core 2.1 new feature Hosted Services, I see that they are very similarly modelled to QueueBackgroundWorkItem

The Queue Background work item seems to have a limitation that the task must execute within 90 seconds

The AppDomain shutdown can only be delayed 90 seconds (It’s actually the minimum of HttpRuntimeSection.ShutdownTimeout and processModel shutdownTimeLimit). If you have so many items queued that they can’t be completed in 90 seconds, the ASP.NET runtime will unload the AppDomain without waiting for the work items to finish.

Do hosted services have different behaviors or does this limitation still apply?

I'm worried that if I queue something on my hosted service, if it's a really long running task, is it still guaranteed to complete?

Answer 1

As part of trying to gracefully shut down the web host builds a cancellation token in combination with the configured ShutdownTimeout

var timeoutToken = new CancellationTokenSource(Options.ShutdownTimeout).Token;
if (!cancellationToken.CanBeCanceled)
{
    cancellationToken = timeoutToken;
}
else
{
    cancellationToken = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutToken).Token;
}

Source

This becomes the shut down token when stopping hosted services

// Fire the IHostedService.Stop
if (_hostedServiceExecutor != null)
{
    await _hostedServiceExecutor.StopAsync(cancellationToken).ConfigureAwait(false);
}

In researching the potential issues with hosted services I came across the following from official documentation.

Deployment considerations and takeaways

It is important to note that the way you deploy your ASP.NET Core WebHost or .NET Core Host might impact the final solution. For instance, if you deploy your WebHost on IIS or a regular Azure App Service, your host can be shut down because of app pool recycles. But if you are deploying your host as a container into an orchestrator like Kubernetes or Service Fabric, you can control the assured number of live instances of your host. In addition, you could consider other approaches in the cloud especially made for these scenarios, like Azure Functions.

But even for a WebHost deployed into an app pool, there are scenarios like repopulating or flushing application’s in-memory cache, that would be still applicable.

The IHostedService interface provides a convenient way to start background tasks in an ASP.NET Core web application (in .NET Core 2.0) or in any process/host (starting in .NET Core 2.1 with IHost). Its main benefit is the opportunity you get with the graceful cancellation to clean-up code of your background tasks when the host itself is shutting down.

Now from this based on your concerns I would gather that there is no guarantee that your long running tasks will complete, but they may be given the opportunity for a graceful cancellation based on the hosting environment as explained in the quoted statement above.