Loop through a list of strings in parallel, return

Question

I have a list of strings that I need to perform some action on. Below is a simple piece of code that works perfectly.

I'd like to speed up the execution of the "ProcessList()" method and my understanding is that I could implement some parallel processing so the strings get processed in parallel rather than serially.

I've done some searching but I'm fairly new to this parallel processing stuff so I'm not even sure what exactly to be searching for. A simple code sample or link to a very similar example would be immensely helpful.

Note: I'm working with .NET 3.5 so the "System.Threading.Tasks" library isn't available. If at all possible I'd like to be able to do it with .NET 3.5 out of the box without downloading additional libraries.

using System.Collections.Generic;
using System;

class Program
{
    static void Main(string[] args)
    {
        // get a list of strings
        var list = new List<string>() { "item1", "item2", "item3", "item4" };

        // process the list
        var resultList = ProcessList(list);

        // print out the results of the list
        resultList.ForEach(x => Console.WriteLine(x));
        Console.ReadLine();
    }

    private static List<string> ProcessList(List<string> list)
    {
        // create list to return
        var resultList = new List<string>();

        // loop through each string in the list and call the "ProcessString()" method for each one
        list.ForEach(x => resultList.Add(ProcessString(x)));

        // return list of processed strings
        return resultList;
    }

    private static string ProcessString(string input)
    {
        // do something here
        return input.ToUpper();
    }
}

Answer 1

Few examples you can start reading to create your own implementation for processing strings:

A Simple Parallel.ForEach Implementation in .NET 3.5

Parallel ForEach Loops in C# 3.5

Optimized Parallel ForEach .NET 3.5

But if it is feasible to use external library then I recommend using Task Parallel Library it is already available from NuGet

Parallel.ForEach()

It provides ways to manage your MaxDegreeOfParallelism and Scheduler options which has to be managed by yourself if you creating your own implementation.