CustomTaskConsoleApplication

CustomTaskConsoleApplication

using System;
using System.Runtime.CompilerServices;
using System.Threading;

namespace CustomTaskConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            Task job = AsyncMethod();

            Console.WriteLine("Do some job");
            Console.WriteLine("Main thread is waiting...");
            Task.WaitAny(job);
            Console.ReadKey();
        }

        public static async Task AsyncMethod()
        {
            Console.WriteLine("Sync part of async method");
            await new Promise(()=> Thread.Sleep(3000));

            Console.WriteLine("Continuation");
        }
    }

    #region CustomAwaiter - Stupid and simplest awaiter implementation
    public class CustomAwaiter : ICriticalNotifyCompletion
    {
        private readonly Promise _promise;
        public CustomAwaiter(Promise promise)
        {
            _promise = promise;
        }

        public bool IsCompleted
        {
            get { return _promise.IsCompleted; }
        }

        public void OnCompleted(Action continuation)
        {
            _promise.ContinueWith(continuation);
        }

        public void UnsafeOnCompleted(Action continuation)
        {
            OnCompleted(continuation);
        }

        public void GetResult()
        {
            _promise.Wait();
        }
    }
    #endregion

    #region Promise - Stupid and simplest Task implementation
    public class Promise
    {
        private Action _continuation;

        public Promise(Action action)
        {
            ThreadPool.QueueUserWorkItem((o) =>
            {
                action();
                IsCompleted = true;
                _continuation();
            });
        }

        public bool IsCompleted { private set; get; }

        public CustomAwaiter GetAwaiter()
        {
            return new CustomAwaiter(this);
        }

        public void ContinueWith(Action continuation)
        {
            _continuation = continuation;
        }

        public void Wait()
        {
            if (!IsCompleted)
            {
                SpinWait.SpinUntil(() => IsCompleted);
            }
        }
    }
    #endregion
}