static void Main(string[] args)
        {
             //ThreadPool.SetMinThreads(100, 100); // 100 ядерный процессор
             while (1 == 1)
             {
                 //Console.WriteLine(++_indexRun);
                 Task.Run(() => { Job(++_indexRun); });
             }
        }

        static int Job(int run)
        {
            Thread.Sleep(2000);
            Console.WriteLine($" job {run} done");
            return run;
        }

 class Program
    {
        private static int _indexRun;
        static void Main(string[] args)
        {
            while (1 == 1)
            {
                new Thread(() => { Job(++_indexRun); }).Start();
            }          
        }

       static int Job(int run)
        {
            Thread.Sleep(2000);
            Console.WriteLine($" job {run} done");
            return run;
        }
    }