How background worker usage in ASP.NET Core resuce load time

Question

i have read this article https://blog.elmah.io/async-processing-of-long-running-tasks-in-asp-net-core/

first this article simulate a long running operation like

public async Task<IActionResult> Index()  
{  
    await CallSlowApi();  
    return View();  
}  
  
private async Task CallSlowApi()  
{  
    _logger.LogInformation($"Starting at {DateTime.UtcNow.TimeOfDay}");  
    await Task.Delay(10000);  
    _logger.LogInformation($"Done at {DateTime.UtcNow.TimeOfDay}");  
}  

with above approach page took 10 seconds and 30 milliseconds to load but the moment does the same job by ASP.NET Core background service then page took 13 milliseconds

i like to know how load reduce to 13 milliseconds ?

what these two line of code is doing ?

services.AddHostedService<LongRunningService>();  
services.AddSingleton<BackgroundWorkerQueue>();  

please some one help me to understand.

Thanks

Answer 1

the performance gain is by return the html before the long running task completes. while a background service is better management of threads, you could just:

 public IActionResult Index()   
 {   
     // start and don't wait   
     Thread.Run(() => CallSlowApi());   
   
     // return page -- the slowapi will complete after the html is returned   
     return View();   
 }