using System;

using System.Threading;

using System.Threading.Tasks;   

​

public class Program

{

    public static async Task Main()

    {

        Console.WriteLine("Start");

        var t1 = ShortWork("SW1");

        var t2 = ShortWork("SW2");

        await Task.Delay(50);

        var t3 = LongWork("LW1");

        await Task.WhenAll(t1, t2);

        await t3;

        Console.WriteLine("Done");

    }

    public static async Task ShortWork(string name)

    {

        Console.WriteLine($"SHORT Start {name} Thread={Thread.CurrentThread.ManagedThreadId}");

        await Task.Delay(500);

        Console.WriteLine($"SHORT End {name} Thread={Thread.CurrentThread.ManagedThreadId}");

    }

    public static async Task LongWork(string name)

    {

        Console.WriteLine($"LONG Start {name} Thread={Thread.CurrentThread.ManagedThreadId}");

        await Task.Delay(2500);

        Console.WriteLine($"LONG End {name} Thread={Thread.CurrentThread.ManagedThreadId}");

    }

}