using System;

using System.Threading.Tasks;

using System.Threading;

public class Program

{

    public static void Main()

    {

        Test().Wait();

    }

    public static async Task Test(){

        var o = new object();

        lock(o){

            Console.WriteLine(Thread.CurrentThread.ManagedThreadId);

            await Task.Delay(100);

            Console.WriteLine(Thread.CurrentThread.ManagedThreadId);

        }

    }

}

​