Got "Index out of bounds" Error on List.Add() in c# Parallel.ForEach

Question

Here is the code

List<string> something = new List<string>();
Parallel.ForEach(anotherList, r =>
     {
            .. do some work
             something.Add(somedata);
      });

I get the Index out of bounds error around 1 time per hundred run. Is there anyway to prevent the conflict (I assume) caused by threading?

Answer 1

In order to prevent the issue, instead of List you may use ConcurrentQueue or similar Concurrent collections in your parallel part. Once the parallel task is done, you can put it in the List<T>.

For more information take a look at System.Collections.Concurrent namespace to find the suitable collection for your use case.