using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public void Main()

    {       

            var options = new ParallelOptions() { MaxDegreeOfParallelism = 2 };

            Parallel.For(0, 10, i => ExecTaskSync(i));

            Parallel.For(0, 10, async i => await ExecTask(i));

            Console.WriteLine("ALL DONE.");

    }

    // Define other methods and classes here

    async Task<int> ExecTask(int index)

    {

            Console.WriteLine("Task {0} starting.", index);

            await Task.Delay(1000);

            Console.WriteLine("Task {0} done.", index);

            return index;

    }

    int ExecTaskSync(int index)

    {

            Console.WriteLine("Sync Task {0} starting.", index);

            Thread.Sleep(1000);

            Console.WriteLine("Sync Task {0} done.", index);

            return index;

    }

}