Cómo escribir un demonio de Linux con .Net Core

Lo mejor que se me ocurre se basa en la respuesta a otras dos preguntas:Matar correctamente un demonio .NET Core que se ejecuta en Linux y ¿Es posible esperar un evento en lugar de otro método asincrónico?

using System;
using System.Runtime.Loader;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    public class Program
    {
        private static TaskCompletionSource<object> taskToWait;

        public static void Main(string[] args)
        {
            taskToWait = new TaskCompletionSource<object>();

            AssemblyLoadContext.Default.Unloading += SigTermEventHandler;
            Console.CancelKeyPress += new ConsoleCancelEventHandler(CancelHandler);

            //eventSource.Subscribe(eventSink) or something...

            taskToWait.Task.Wait();

            AssemblyLoadContext.Default.Unloading -= SigTermEventHandler;
            Console.CancelKeyPress -= new ConsoleCancelEventHandler(CancelHandler);

        }


        private static void SigTermEventHandler(AssemblyLoadContext obj)
        {
            System.Console.WriteLine("Unloading...");
            taskToWait.TrySetResult(null);
        }

        private static void CancelHandler(object sender, ConsoleCancelEventArgs e)
        {
            System.Console.WriteLine("Exiting...");
            taskToWait.TrySetResult(null);
        }

    }
}

Jugué con una idea similar a cómo .net core web host espera el apagado en las aplicaciones de la consola. Lo estaba revisando en GitHub y pude extraer la esencia de cómo realizaron el Run

https://github.com/aspnet/Hosting/blob/15008b0b7fcb54235a9de3ab844c066aaf42ea44/src/Microsoft.AspNetCore.Hosting/WebHostExtensions.cs#L86

public static class ConsoleHost {
    /// <summary>
    /// Block the calling thread until shutdown is triggered via Ctrl+C or SIGTERM.
    /// </summary>
    public static void WaitForShutdown() {
        WaitForShutdownAsync().GetAwaiter().GetResult();
    }


    /// <summary>
    /// Runs an application and block the calling thread until host shutdown.
    /// </summary>
    /// <param name="host">The <see cref="IWebHost"/> to run.</param>
    public static void Wait() {
        WaitAsync().GetAwaiter().GetResult();
    }

    /// <summary>
    /// Runs an application and returns a Task that only completes when the token is triggered or shutdown is triggered.
    /// </summary>
    /// <param name="host">The <see cref="IConsoleHost"/> to run.</param>
    /// <param name="token">The token to trigger shutdown.</param>
    public static async Task WaitAsync(CancellationToken token = default(CancellationToken)) {
        //Wait for the token shutdown if it can be cancelled
        if (token.CanBeCanceled) {
            await WaitAsync(token, shutdownMessage: null);
            return;
        }
        //If token cannot be cancelled, attach Ctrl+C and SIGTERN shutdown
        var done = new ManualResetEventSlim(false);
        using (var cts = new CancellationTokenSource()) {
            AttachCtrlcSigtermShutdown(cts, done, shutdownMessage: "Application is shutting down...");
            await WaitAsync(cts.Token, "Application running. Press Ctrl+C to shut down.");
            done.Set();
        }
    }

    /// <summary>
    /// Returns a Task that completes when shutdown is triggered via the given token, Ctrl+C or SIGTERM.
    /// </summary>
    /// <param name="token">The token to trigger shutdown.</param>
    public static async Task WaitForShutdownAsync(CancellationToken token = default (CancellationToken)) {
        var done = new ManualResetEventSlim(false);
        using (var cts = CancellationTokenSource.CreateLinkedTokenSource(token)) {
            AttachCtrlcSigtermShutdown(cts, done, shutdownMessage: string.Empty);
            await WaitForTokenShutdownAsync(cts.Token);
            done.Set();
        }
    }

    private static async Task WaitAsync(CancellationToken token, string shutdownMessage) {
        if (!string.IsNullOrEmpty(shutdownMessage)) {
            Console.WriteLine(shutdownMessage);
        }
        await WaitForTokenShutdownAsync(token);
    }


    private static void AttachCtrlcSigtermShutdown(CancellationTokenSource cts, ManualResetEventSlim resetEvent, string shutdownMessage) {
        Action ShutDown = () => {
            if (!cts.IsCancellationRequested) {
                if (!string.IsNullOrWhiteSpace(shutdownMessage)) {
                    Console.WriteLine(shutdownMessage);
                }
                try {
                    cts.Cancel();
                } catch (ObjectDisposedException) { }
            }
            //Wait on the given reset event
            resetEvent.Wait();
        };

        AppDomain.CurrentDomain.ProcessExit += delegate { ShutDown(); };
        Console.CancelKeyPress += (sender, eventArgs) => {
            ShutDown();
            //Don't terminate the process immediately, wait for the Main thread to exit gracefully.
            eventArgs.Cancel = true;
        };
    }

    private static async Task WaitForTokenShutdownAsync(CancellationToken token) {
        var waitForStop = new TaskCompletionSource<object>();
        token.Register(obj => {
            var tcs = (TaskCompletionSource<object>)obj;
            tcs.TrySetResult(null);
        }, waitForStop);
        await waitForStop.Task;
    }
}

Intenté adaptar algo como un IConsoleHost pero rápidamente me di cuenta de que lo estaba sobredimensionando. Extrajo las partes principales en algo como await ConsoleUtil.WaitForShutdownAsync(); que operaba como Console.ReadLine

Esto permitió que la utilidad se usara así

public class Program {

    public static async Task Main(string[] args) {
        //relevant code goes here
        //...

        //wait for application shutdown
        await ConsoleUtil.WaitForShutdownAsync();
    }
}

a partir de ahí creando un systemd como en el siguiente enlace, debería obtener el resto del camino

Escribiendo un demonio de Linux en C#