using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    static Task _task = Task.CompletedTask;

    static object _mutex = new object();

    static void Queue(int i)

    {

        lock (_mutex)

        {

            _task = _task.ContinueWith(_ => {

                Thread.Sleep(1);

            }).ContinueWith(_ => {

                if ((i % 100) == 0)

                {

                    System.Console.WriteLine($"Done {System.GC.GetTotalMemory(true)}");         

                }           

            });

        }

    }

​

    public static async Task Main()

    {

        for(int i = 0; i < 1000; i++)

        {

            Queue(i);

            if ((i % 100) == 0)

            {

                System.Console.WriteLine(System.GC.GetTotalMemory(true));

            }

        }

        System.Console.WriteLine("Finished Queuing");

        await _task;

        System.Console.WriteLine($"Finished running {System.GC.GetTotalMemory(true)}");

    }

}