using System;

using System.Threading.Tasks;       

​

public class Program

{

    public static int Counter = 1;

​

    public static void Main()

    {

        var foo = Do().Result;

        System.Threading.Thread.Sleep(1000);

        Console.WriteLine(foo);

    }

    public static async Task<string> Do()

    { 

        var x = await DoWithYield(awaited: true);

        Console.WriteLine($"{Counter++} Main with await.");

        DoWithYield(awaited: false);

        Console.WriteLine($"{Counter++} Main without await.");

        return x;

    }

    public static async Task<string> DoWithYield(bool awaited) 

    {

        // yields control to the caller, 

        // until the caller either finishes or awaits.

        await Task.Delay(1000);

        await Task.Yield(); 

        await Task.FromResult(0);

        if(awaited)

        {

            Console.WriteLine($"{Counter++} If main does await, we should see Main after this message.");

​

        }

        else

        {

            Console.WriteLine($"{Counter++} If main does not await, then this runs at a non-deterministic time.");

        }

        return "Done.";

    }

}