Parallel programming in c# 4.0

In our daily programming routine we use thread mechanism to parallelize your code to distribute work across multiple processors.  To take advantage of the hardware of today and tomorrow Visual Studio 2010 and the .NET Framework 4 enhance support for parallel programming by providing a new runtime, new class library types, and new diagnostic tools.

Let’s start with a simple concept in parallel programming.

Data Parallelism (Task Parallel Library)

Data Parallelism describes how to create parallel for and foreach loops. In this article we will look into simple for loop in parallel programming world.

In this application I wrote a simple method to calculate the Root of a given number. Let’s look into the executing time of for and Parallel.For loop methods.

The below code took me 16 seconds to execute. I am using 2.8-Ghz dual core 64 bit processor with 4 GB of RAM.

for (int i = 2; i < 20; i++)
            {
                var result = SumRootN(i);
                Console.WriteLine("root {0} : {1} ", i, result);
            }

Instead of a regular for loop I used Parallel.For method and now the execution time got decreased from 16 to 5 seconds

Parallel.For(2, 20, (i) =>
            {
                var result = SumRootN(i);
                Console.WriteLine("root {0} : {1} ", i, result);
            });

When you use the Parallel.For method, the .NET Framework automatically manages the threads that service the loop, so you don’t need to do this yourself. But remember that running code in parallel on two processors does not guarantee that the code will run exactly twice as fast. Nothing comes for free; although you don’t need to manage threads yourself, the .NET Framework still uses them behind the scenes. And of course this leads to some overhead. In fact, if your operation is simple and fast and you run a lot of short parallel cycles, you may get much less benefit from parallelization than you might expect.

Source Code:

namespace ParallelProgramming
{
    using System;
    using System.Diagnostics;
    using System.Threading.Tasks;

    class Program
    {

        static void Main(string[] args)
        {
            var watch = Stopwatch.StartNew();
            
            //
            for (int i = 2; i < 20; i++)
            {
                var result = SumRootN(i);
                Console.WriteLine("root {0} : {1} ", i, result);
            }

            Parallel.For(2, 20, (i) =>
            {
                var result = SumRootN(i);
                Console.WriteLine("root {0} : {1} ", i, result);
            });

            Console.WriteLine(watch.ElapsedMilliseconds);
            Console.ReadLine();
        }

        public static double SumRootN(int root)
        {
            double result = 0;
            for (int i = 1; i < 10000000; i++)
            {
                result += Math.Exp(Math.Log(i) / root);
            }
            return result;
        }
    }