C#•14mo ago

.NET Generic Host Writing "Application Started" when its done with its work

So I have been playing around with the Generic Host (Microsoft.Hosting.Extensions and HostedServices. So I have this output, where "Application started" comes after my service have stopped working. I am not sure about how, I should structure the code to get the "Application Started" before my service runs. I am currently using StartAsync, but gets the same behaviour with RunAsync StartAsync can be seen here: https://source.dot.net/#Microsoft.Extensions.Hosting/Internal/Host.cs,57 My Output

info: MyService[0]
      Service started
info: MyService[0]
      Service done
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Production
info: Microsoft.Hosting.Lifetime[0]
      Content root path: C:\Users\JOAH\source\repos\GenericHost\GenericHost\bin\Debug\net7.0
info: Microsoft.Hosting.Lifetime[0]
      Application is shutting down...
info: MyService[0]
      Service stopped

info: MyService[0]
      Service started
info: MyService[0]
      Service done
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Production
info: Microsoft.Hosting.Lifetime[0]
      Content root path: C:\Users\JOAH\source\repos\GenericHost\GenericHost\bin\Debug\net7.0
info: Microsoft.Hosting.Lifetime[0]
      Application is shutting down...
info: MyService[0]
      Service stopped

My Code

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

var host = Host.CreateDefaultBuilder()
    .UseConsoleLifetime()
    .ConfigureServices(services =>
    {
        services.AddHostedService<MyService>();
    }).ConfigureLogging(loggingBuilder => loggingBuilder.AddConsole())
    .Build();
var cts = new CancellationTokenSource();

await host.StartAsync(cts.Token);
await host.StopAsync();

class MyService : IHostedService
{
    private readonly ILogger<MyService> _logger;

    public MyService(ILogger<MyService> logger)
    {
        _logger = logger;
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Service started");
        await Task.Delay(1000); //Important work, probably
        _logger.LogInformation("Service done");
        return;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Service stopped");
        return Task.CompletedTask;
    }
}

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

var host = Host.CreateDefaultBuilder()
    .UseConsoleLifetime()
    .ConfigureServices(services =>
    {
        services.AddHostedService<MyService>();
    }).ConfigureLogging(loggingBuilder => loggingBuilder.AddConsole())
    .Build();
var cts = new CancellationTokenSource();

await host.StartAsync(cts.Token);
await host.StopAsync();

class MyService : IHostedService
{
    private readonly ILogger<MyService> _logger;

    public MyService(ILogger<MyService> logger)
    {
        _logger = logger;
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Service started");
        await Task.Delay(1000); //Important work, probably
        _logger.LogInformation("Service done");
        return;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("Service stopped");
        return Task.CompletedTask;
    }
}

15 Replies

ffmpeg -i me -f null -•14mo ago

I should structure the code to get the "Application Started" before my service runs

why would you want that?

Hejle•14mo ago

Because currently my services prints that it starts, just as it completes

ffmpeg -i me -f null -•14mo ago

well it does nothing 😐 apart from waiting 1 sec so again why do you care that your service is started before or after "Application Started"?

Hejle•14mo ago

The Thread.Sleep could be swapped out with some real work, like fetching data from an API or something

ffmpeg -i me -f null -•14mo ago

ps it shouldn't be Thread.Sleep but await Task.Delay why do you care when this happens are there dependencies?

Hejle•14mo ago

I am mainly interested how it works, as I could get it working without using a HostedService or even the GenericHost. So I mainly care, because I think the startup messages (printing how to quick, what enviroment its running in and rootpath is good information) While I could make the startup-message myself, it would feel stupid, to have: Startup-message "Work-being-done"-messages Startup-message Closing-message

ffmpeg -i me -f null -•14mo ago

i'm sorry i really don't get what's the issue (also because you didn't finish you phrase up there) StartAsync is called when the application starts you can log stuff in there if you want to what more do you want like are you just saying that you want your logs after the startup messages

Pobiega•14mo ago

hosted services traditionally dont do imperative work once then finish, which is what the code you have shown above does the whole idea of a service is that its a long running thing that has a distinct start and stop phase, normally starting a server or process that does something, perhaps on a timer. so the reason you are getting "unsual" behaviour is that you are essentially missusing the IHostedService structure

Hejle•14mo ago

Which structure would/should I use instead?

Pobiega•14mo ago

well if you just want a program that runs its code once then terminates, you dont need generic host just a normal console app. You could use the hostbuilder to get config/DI setup for you, but then dont start the host, just resolve the actual application class you make instead remember, generic host is for hosting long living processes not running a one-and-done process

Hejle•14mo ago

Yeah, is using it for config/DI

Pobiega•14mo ago

I personally roll my own configbuilder + DI setup for simple console apps, but I can see the appeal in having it "done for you"

public class Program
{
    public static async Task Main()
    {
        var builder = new HostApplicationBuilder();
        builder.Services.AddTransient<MyActualApplicationClass>();

        var host = builder.Build();
        var runner = host.Services.GetRequiredService<MyActualApplicationClass>();

        await runner.RunAsync();
    }
}

public class MyActualApplicationClass
{
    public async Task RunAsync()
    {
        throw new NotImplementedException();
    }
}

public class Program
{
    public static async Task Main()
    {
        var builder = new HostApplicationBuilder();
        builder.Services.AddTransient<MyActualApplicationClass>();

        var host = builder.Build();
        var runner = host.Services.GetRequiredService<MyActualApplicationClass>();

        await runner.RunAsync();
    }
}

public class MyActualApplicationClass
{
    public async Task RunAsync()
    {
        throw new NotImplementedException();
    }
}

something like this

Hejle•14mo ago

Thanks for the help

ffmpeg -i me -f null -•14mo ago

or after having configured services get an ILogger and log what you need but application startup class would be better

Pobiega•14mo ago

yeah you can inject whatever you want into MyActualApplicationClass here a logger, a config object, whatevs

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.NET Generic Host Writing "Application Started" when its done with its work