Parallel For loop versus simple for loop in c#. Speed test

Question

I have some doubt as to whether I should use a Parallel.For(). I did a simple test and it came out strongly against parallelization. In what cases and how to properly use Parallel.For() and PLinq? Here is my test code:

class Wrapper
{
    public void Sequential()
    {
        Stopwatch sw = Stopwatch.StartNew();

        for (int i = 0; i < 1000; i++)
        {
            DauntingOp(i);
            DauntingOp(i + 9000);
            DauntingOp(i - 8521);
            DauntingOp(i);
            DauntingOp(i + 9000);
            DauntingOp(i - 8521);
        }

        Console.WriteLine("For = ms: {0}", sw.ElapsedMilliseconds);
    }

    public void ParallelFor()
    {
        Stopwatch sw = Stopwatch.StartNew();

        Parallel.For(0, 1000, (elem) => 
        {
            DauntingOp(elem);
            DauntingOp(elem + 9000);
            DauntingOp(elem - 8521);
            DauntingOp(elem);
            DauntingOp(elem + 9000);
            DauntingOp(elem - 8521);
        });

        Console.WriteLine("Parallel For = ms: {0}", sw.ElapsedMilliseconds);
    }

    private void DauntingOp(int index)
    {
        try
        {
            long val = index;
            for (int i = 0; i < 1000; i++)
            {
                long a = val + 345678;
                long b = a + 4567;
                long c = a - b;
                long d = long.Parse(new Random().Next().ToString());
                long x = d - a - b - c;
                long y = long.Parse(new Random().Next().ToString()) - (long.Parse(new Random().NextDouble().ToString()) + 345 - x);
            }
        }
        catch { }
        finally
        {
            try
            {
                long a = 345678;
                long b = a + 4567;
                long c = a - b;
                long d = long.Parse(new Random().Next().ToString());
                long x = d - a - b - c;
                long y = long.Parse(new Random().Next().ToString()) - (long.Parse(new Random().Next().ToString()) + 345 - x);
            }
            catch { }
        }
    }

}

class Program
{
    static void Main(string[] args)
    {
        Wrapper wrapper = new Wrapper();
        wrapper.Sequential();
        wrapper.ParallelFor();

        Console.Read();
    }
}

Results:

For = ms: 22645
Parallel For = ms: 29020

Should not be Parallel.For faster?

Answer 1

Run the solution in release mode without debugging.

My system has four cores, which I can see using Task Manager:

And the benchmarking is reliably four times faster:

Note that you won't have multiple cores enabled in Windows 10 by default. You have to run msconfig from your Start menu, and enable multiple processors in the Boot menu: