async_cli.cs

using System;
using System.Threading;
using System.Threading.Tasks;

namespace AsyncCLI
{
    public sealed class Program
    {
        // Main handles command line parsing and invocation
        // of strongly-typed main method.
        public static int Main(string[] args)
        {
            try
            {
                var options = new Options(/*args*/);
                // parse options somehow - use a library!
                // or return (int)ExitCode.InvalidArguments

                return (int)RunProgram(options);
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine(ex);
                return (int)ExitCode.UnexpectedError;
            }
        }

        public sealed class Options
        {
        }

        // Possible exit codes of the program:
        public enum ExitCode
        {
            Success = 0,
            Cancelled = 1,
            InvalidArguments = 2,
            UnexpectedError = -1,
        }

        // Strongly-typed main method. Testing is easier via this entrypoint.
        public static ExitCode RunProgram(Options options)
        {
            using (var cts = new CancellationTokenSource())
            {
                ConsoleCancelEventHandler consoleCancellationHandler = 
                    (sender, eventArgs) =>
                    {
                        eventArgs.Cancel = true;
                        cts.Cancel();
                        Console.Error.WriteLine("Requesting cancellation...");
                    };

                Console.CancelKeyPress += consoleCancellationHandler;

                try
                {
                    // set up, e.g. loggers and other low-level dependencies:
                    var dependency1 = new object();
                    var dependency2 = new object();

                    new Program(dependency1, dependency2)
                        .Run(cts.Token)
                        .Wait(cts.Token); // must be passed to Wait to throw OperationCanceledException

                    return ExitCode.Success;
                }
                catch (AggregateException ex)
                {
                    foreach (var inner in ex.InnerExceptions)
                    {
                        Console.Error.WriteLine(inner);
                    }

                    return ExitCode.UnexpectedError;
                }
                catch (OperationCanceledException)
                {
                    Console.Error.WriteLine("Cancelled.");
                    return ExitCode.Cancelled;
                }
                finally
                {
                    Console.CancelKeyPress -= consoleCancellationHandler;
                }
            }
        }

        public Program(object injected, object dependencies)
        {
        }

        public async Task Run(CancellationToken ct)
        {
            Console.WriteLine("Sleeping...");
            await Task.Delay(TimeSpan.FromSeconds(5), ct);
            Console.WriteLine("Woke up!");
        }
    }
}