using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("1 " + Thread.CurrentThread.ManagedThreadId); //runs on main

        FooAsync();

        Console.WriteLine("3 " + Thread.CurrentThread.ManagedThreadId); //runs on main

    }

​

​

    private static async void FooAsync()

    {

        await Task.Yield();

       Console.WriteLine("2 " + Thread.CurrentThread.ManagedThreadId);  //runs on different thread

    }

}