using System;

using System.IO;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Threading;

using System.Threading.Tasks;

​

​

public class Program

{

    public static void Main()

    {

        //SimpleParallelFor();

        ParallelForWithThreadLocalVariables();

    }

    private static void SimpleParallelFor() 

    {

        ParallelLoopResult result = Parallel.For(0, 100, index => CalculateSum(index));

        Console.WriteLine(result.IsCompleted);

    }

    private static void CalculateSum(int index) 

    {

        Random rnd = new Random(index * 100000);

        Byte[] bytes = new Byte[100];

        rnd.NextBytes(bytes);

        int sum = 0;

        foreach(var byt in bytes)

        {

            sum += byt;

        }

        Console.WriteLine($"Index: {index}, Sum: {sum}");

    }

    private static void ParallelForWithThreadLocalVariables() 

    {

        int[] nums = Enumerable.Range(0, 1000000).ToArray();

        long total = 0;

​

        Parallel.For<long>(

            0, 

            nums.Length, 

            () => 0, 

            (index, loopState, subtotal) =>

            {

                subtotal += nums[index];

                return subtotal;

            },

            (subTotal) => Interlocked.Add(ref total, subTotal)

        );

​

        Console.WriteLine("The total is {0:N0}", total);

    }

}

​