Shows how the .NET Threadpool creates new threads.

ThreadPool.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
	class Program
	{
		static void Main(string[] args)
		{
			Console.WriteLine(GetActiveThreads());

			while (true)
			{
				Thread.Sleep(100);
				Task.Run(() => Thread.Sleep(TimeSpan.FromMinutes(10)));

				Console.WriteLine(GetActiveThreads());
			}
		}

		static int GetActiveThreads()
		{
			ThreadPool.GetMaxThreads(out int maxWorker, out int maxIo);
			ThreadPool.GetAvailableThreads(out int worker, out int io);

			return maxWorker - worker;
		}
	}
}