List thread safety

Question

I am using the below code

var processed = new List();
Parallel.ForEach(items, item => 
{
    processed.Add(SomeProcessingFunc(item));
});
         


        

Answer 1

As alternative to the answer of Andrey:

items.AsParallel().Select(item => SomeProcessingFunc(item)).ToList();

You could also write

items.AsParallel().ForAll(item => SomeProcessingFunc(item));

This makes the query that is behind it even more efficient because no merge is required, MSDN. Make sure the SomeProcessingFunc function is thread-safe. And I think, but didn't test it, that you still need a lock if the list can be modified in an other thread (adding or removing) elements.