c# - async, await

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

namespace AsyncAwaitDemo
{
    public delegate Task MyDelegate();

    class Program
    {
        static async void Call()
        {
            int x = await Task.Run<int>(() => { Thread.Sleep(3500); return 100; });
            Console.WriteLine("From Call():" + x);
        }

        static void Main(string[] args)
        {
            Call();

            LongCallWithCallback((i) => 
            {
                Console.WriteLine("Execution done." + i);
            });

            CallAsyncTask(async () => 
            {
                int x = 0;
                await Task.Run(() => 
                {
                    Thread.Sleep(3000);
                    x = 100;
                });

                Console.WriteLine("Got value:" + x);
            });

            while (true)
            {
                Console.WriteLine("Main thread working...");
                Thread.Sleep(500);
            }
        }

        private static void CallAsyncTask(MyDelegate myDelegate)
        {
            myDelegate();
        }

        private static MyDelegate GetATask()
        {
            return LongCallToReturn;
        }

        public static Task<int> LongCallToReturn()
        {
            return Task.Run<int>(() =>
            {
                Thread.Sleep(3000);
                return 100;
            });
        }

        public static async void LongCallWithCallback(Action<int> afterExecution)
        {
            int x = await Task.Run<int>(() =>
            {
                Thread.Sleep(5000);
                return 100;
            });

            // Call back.
            afterExecution(x);
        }
    }
}

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

namespace Async2Await
{
    class Program
    {
        static void Main(string[] args)
        {
            ProcessAsync();
            while (true)
            {
                Thread.Sleep(1000);
                Console.WriteLine("Main working...");
            }
        }

        private static async void ProcessAsync()
        {
            await Task.Run(() =>
            {
                Thread.Sleep(5000);
                Console.WriteLine("p1...");
            });

            await Task.Run(() =>
            {
                Thread.Sleep(5000);
                Console.WriteLine("p2...");
            });

            Console.WriteLine("End of ProcessAsync()");
        }
    }
}