I have seen few articles around about how to execute long-running tasks in a BackgroundService and most of them do the same mistake. The code looks more or less like this:

public class MyWorker : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken cancellationToken)
    {
        while(!cancellationToken.IsCancellationRequested)
        {
            await DoSomethingAsync();
        }
    }
}

This code will run your async operation and stop anything else from happening.

So, if your goal is to have a background worker running some operation in a loop (for example, polling messages from a queue), the right approach would be to spin up a separate task inside ExecuteAsync. Something like this:

public class MyWorker : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken cancellationToken)
    {
        await Task.Factory.StartNew(async () =>
        {
            await this.ExecuteAsyncCore(cancellationToken).ConfigureAwait(false);
        }, cancellationToken);
    }

    private async Task ExecuteAsyncCore(CancellationToken cancellationToken)
    {
        while(!cancellationToken.IsCancellationRequested)
        {
            await DoSomethingAsync();
        }
    }
}

As usual, I created a small repository on GitHub to help you better understand what’s going on here.

In the repo we have a simple Minimal Api with a GET endpoint /counter. A background service is used to increase a counter variable. Calling the endpoint will return its current value. It’s a very simple scenario, but basically shows how a background service can perform a long running operation (in a loop) and how we can query its state from an API.

Now, in the appsetting you can configure whether you want the background service to be blocking or not.

You’ll see that when the value is true, the /counter endpoint cannot be reached.

Cheers!

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