startnew.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http;

namespace StartNewIsDangerous.Controllers
{
    public class ValuesController : ApiController
    {
        private static List<Task<ThreadInfo>> _CurrentTasks;
        // GET api/values/5
        
        public string Get(int id)
        {
            _CurrentTasks = new List<Task<ThreadInfo>>();

            for (var i = 0; i < id; i++)
            {
                _CurrentTasks.Add(DoItOnBackground());
            }

            return "Tasks started";
        }

        public List<ThreadInfo> Get()
        {
            Task.WaitAll(_CurrentTasks.ToArray());
            return _CurrentTasks.Select(x => x.Result).ToList();
        }

        private static Task<ThreadInfo> DoItOnBackground()
        {
            return Task.Factory.StartNew(() =>
            {
                var currentThread = Thread.CurrentThread;

                Thread.Sleep(TimeSpan.FromSeconds(1));
                return new ThreadInfo
                {
                    IsThreadPool = currentThread.IsThreadPoolThread,
                    ThreadId = currentThread.ManagedThreadId
                };
            });
        }
    }

    public class ThreadInfo
    {
        public int ThreadId { get; set; }
        public bool IsThreadPool { get; set; }

        public override string ToString()
        {
            return $"ThreadID {ThreadId} IsThreadPool {IsThreadPool}";
        }
    }
}