Exit the application with exit code from async thread

Question

My .NET5 Web API project (in addition to REST) listens to Telegram messages. The goals are simple:

when a user sends exit message - terminate the app with exit code 8
when a message handler throws a SeriousException - terminate the app with exit code 8

Unfortunately, due to the asynchronous nature of message polling, I'm struggling to achieve this goal. I've prepared a sample project in GitHub: https://github.com/chris-rutkowski/AsExPoC .

I found many similar subjects on Stack Overflow but nothing really works for me, moreover the plenty of suggested solutions (some AsyncHelpers etc) seems like overkill. I was thinking about passing Thread.CurrentThread to the service and somehow throw the exception on it, but I don't know how, or if it's event possible and even if it is, is it is a best practice. I don't have that much knowledge in C#+.NET, but In Swift (iOS), I would solve it so easily, just 3 lines including curly brackets:

  DispatchQueue.main.async {
      throw ForcedExitException()
  }

This is my stripped down .NET5 Web Api, you can find in the repo.

Program.cs

public class Program
    {
        public static int Main(string[] args)
        {
            try
            {
                var host = CreateHostBuilder(args).Build();
                var service = host.Services.GetRequiredService<DummyService>();
                service.Run();

                // other services are running too - I cannot just wait for DummyService to throw the exception

                host.Run();

                return 0;
            }
            catch (ForcedExitException)
            {
                return 8;
            }
            catch (Exception ex)
            {
                return 1;
            }
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }

DummyService.cs

    public class DummyService
    {
        private readonly DummyMessenger _dummyMessenger;

        public DummyService()
        {
            _dummyMessenger = new DummyMessenger();
        }

        public async void Run()
        {
            _dummyMessenger.StartReceiving();
            _dummyMessenger.Add(async (_, message) => {
                Console.WriteLine($"received message {message}");
                await Task.Delay(50);

                if (message == "exit") 
                    throw new ForcedExitException();
            });
        }
    }

What I expect:

Exited with error code 8

This is what I see in the Console:

Exited with error code 134, with the following stacktrace
Unhandled exception. AsExPoC.ForcedExitException: Exception of type 'AsExPoC.ForcedExitException' was thrown.
at AsExPoC.DummyService.<>c.<Run>b__2_0(Object _, String message) in /Users/chris/Developer/Projects/AsExPoC/AsExPoC/DummyService.cs:line 36
at AsExPoC.DummyMessenger.StartReceiving() in /Users/chris/Developer/Projects/AsExPoC/AsExPoC/DummyMessenger.cs:line 27
at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__140_1(Object state)
at System.Threading.QueueUserWorkItemCallbackDefaultContext.Execute()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()

Appreciate feedback.

I haven't given this too much thought, but have you tried Environment.Exit(Int32) — TheGeneral
– TheGeneral, Commented Jul 15, 2021 at 4:08
@TheGeneral thanks for showing interest. It doesn't change anything. I have created the sample project on GitHub: github.com/chris-rutkowski/AsExPoC . Meanwhile, I will update my question to be simpler. — Chris Rutkowski
– Chris Rutkowski, Commented Jul 15, 2021 at 5:57

Jeremy Lakeman · Accepted Answer · 2021-07-15 06:36:47Z

3

I would start by moving your long running service into an IHostedService, forcing the host to stop if the service ever stops;

public class DummyService : BackgroundService
{
    private readonly IHostApplicationLifetime lifetime;

    public DummyService(IHostApplicationLifetime lifetime)
    {
        this.lifetime = lifetime;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        try
        {
            while (true)
            {
                //...
            }
        }
        catch (Exception)
        {
            Environment.ExitCode = 8;
        }
        lifetime.StopApplication();
    }
}

Then you can return Environment.ExitCode from your main method, or leave it as void return.

answered Jul 15, 2021 at 6:36

Jeremy Lakeman

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