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Parallel Computing: PLINQ

Visual Studio 2010 has new API for LINQ (Language Integrated Query). This helps us to implement the power of Parallel Computing in declarative manner.


LINQ without Parallel Extension


It will take 3 sec for 28 thousand elements.


static void Main(string[] args)


{


    Stopwatch sw = Stopwatch.StartNew();


   


    DoIt();


 


    Console.WriteLine(“Elapsed = “ + sw.ElapsedMilliseconds.ToString());


    Console.ReadLine();


}


 


private static void DoIt()


{


    IEnumerable<int> arrInt = Enumerable.Range(1, 4000000);


    var q =


        from n in arrInt


        where IsPrime(n)


        select n.ToString();


 


    List<string> list = q.ToList();


 


    Console.WriteLine(“Elements : “ + list.Count.ToString());


}


 


private static bool IsPrime(int p)


{


    //Find the prime number


    int upperBound = (int)Math.Sqrt(p);


    for (int i = 2; i < upperBound; i++)


    {


        if (p % i == 0) return false;


    }


    return true;


}


 


LINQ with Parallel Extension


With a very simple change in query this will take around 1.5 sec for the same number of elements.


var q =


    from n in arrInt.AsParallel()


    where IsPrime(n)


    select n.ToString();


 


Greenroom


What’s the magic? When we use .AsParallel() it does cast the list of integers into ParallelEnumerable class and calls a different Where method which implements the new “Task” API.


With Lambda expression this would look more clear.


Before


var q = arrant


    .Where(n => IsPrime(n))


    .Select(n => n.ToString());


 


Class: Enumerable


 


Method:     


        public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate);


 


After (while using AsParallel())


Code:


var q = arrInt.AsParallel()


    .Where(n => IsPrime(n))


    .Select(n => n.ToString());


 


Class : ParallelEnumerable


 


Method :


        public static ParallelQuery<TSource> Where<TSource>(this ParallelQuery<TSource> source, Func<TSource, bool> predicate);


 


The above time will vary based on CPU power and availability.


Namoskar!!!