使用 .NET 通用主机的控制台应用程序过早退出

Question

I'm trying to add console commands to an existing ASP.NET Core 5 web application. The important part here is that I can set up all the dependency injection and configuration that is in the web application and use it in the console application as well. To do that I'm using the .NET Generic host in the following way:

public class ConsoleHostedService : IHostedService
{
    private readonly IHostApplicationLifetime appLifetime;

    public ConsoleHostedService(IHostApplicationLifetime appLifetime)
    {
      this.appLifetime = appLifetime;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
      appLifetime.ApplicationStarted.Register(() =>
      {
        Task.Run(async () =>
          {
            try {
         
              Console.WriteLine("1");
              await Task.Delay(1000);
              Console.WriteLine("2");
            }
            catch (Exception ex)
            {
              Console.WriteLine(ex.ToString());
            }
            finally
            {
              // Stop the application once the work is done
              appLifetime.StopApplication();
            }
          });
      });

      return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
      return Task.CompletedTask;
    }

  }
}

This Host is executed from the following code:

public static void ExecuteCommand(string[] args)
    {
      Parser.Default.ParseArguments<CommandOptions1, CommandOptions2>(args)
        .WithParsed<CommandOptions1>(async options =>
        {
          try
          {
            await Host.CreateDefaultBuilder(args)
              .ConfigureServices((hostContext, services) =>
              {
                // configuration of dependency injection here

                services.AddHostedService<ConsoleHostedService>();
              })
              .RunConsoleAsync();
          }
          catch (Exception e)
          {
            Console.WriteLine(e);
          }
        })
        .WithParsed<CommandOptions2>(o =>
        {
          // different command here
        });
    }
  }

I'm using the CommandLineParser library here, though this part shouldn't matter for the problem. The actual generic host code was adapted from this blog post , which did seem to adress exactly what I needed.

The Problem is that the console application exits early, in my example where the await Task.Delay(1000) stands as a placeholder for my actual code I added some logging. The first line "1" is written to the console, the second line "2" is never written. I also get output for Microsoft.Hosting.Lifetime about the application stopping. The application seems to stop itself the moment it became ready, and any work I do in there that takes a bit of time is never executed at all.

I double checked all async/awaits and they're all there, the issue isn't a forgotten await. It does seem to be something about the Generic Host or the Lifetime itself, but those parts are pretty much entirely taken from the blog post I linked. I looked over all parts here, but I can't see any reason why the code would just shut down immediately.

Any idea what I'm doing wrong here, or what might cause the early shutdown?

Answer 1

Somewhere in the main console program it needs to know when to leave. Having it run an async call means that the program flow returns immediately after the setup call. Hence the console app is heading to the exit without waiting. You need to halt the console until the process ends.

In the main console app do something like:

Task.WaitAll( {the task(s) launched by the app} );

So the main program will halt its process execution flow while the other async processes run and smart wait until all of those task(s) are finished.

Or have some type of signal process to be sent when the async process ends and have the app check for that and shut down after it gets that event.