using System;

using System.Linq;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

    static void Main()

    {

        ThreadPool.SetMinThreads(4, 4);

        //ThreadPool.SetMaxThreads(4, 4);

        Task[] tasks = new[] { 'A', 'B' }.Select(name => Task.Run(() =>

        {

            Thread.Sleep(100); if (name == 'B') Thread.Sleep(500);

            Print($"{name}-Starting");

            var options = new ParallelOptions() { MaxDegreeOfParallelism = 10 };

            Parallel.ForEach(Enumerable.Range(1, 10), options, item =>

            {

                Print($"{name}-Processing #{item}");

                Thread.Sleep(1000);

            });

            Print($"{name}-Finished");

        })).ToArray();

        Task.WaitAll(tasks);

    }

​

    static void Print(string line)

    {

        Console.WriteLine($@"{DateTime.Now:HH:mm:ss.fff} [{Thread.CurrentThread

            .ManagedThreadId}] > {line}");

    }

}