how to speed up populating a list using TPL(task parallel library) in c#

Question

I have following piece of code

List<GridVM> _itemsSource = new List<GridVM>();

  foreach(var shelf in Network.Shelves)
   {
        foreach(var equipment in shelf.Equipment)
        {
          var gridVM= new GridVM(equipment);
          itemSource.Add(gridVM);
         }
   }

here _itemSource is a collection that is going to be data source for a grid.

now creating each vm object for each equipment is taking little bit time ~~around 8 seconds. I want to speed up grid data source population using TPL by running inner forloop in different thread and add the vm to the main collection of _itemSource.

How to achieves so using TPL. Will it really speed up my job considering the facts thread overheads and locking overheads. I can convert current list item source to ConcurrentList or ConcurrntBag. but same question :-will it really give any boost or not. if not, then I am interest to know why??

Answer 1

You can easily parallelize your code using PLINQ (aka Parallel Linq):

var _itemsSource = Network.Shelves
    .SelectMany(s => s.Equipment)
    .AsParallel()
    .Select(e => new GridVM(e))
    .ToList();

It may execute faster if the constructor takes time. If the overhead is just "adding items to a list" then you'll gain nothing. That said, if it takes 8 seconds just to add items to the list, then you definitely have other problems, such as memory consumption.