Question

Is the following pseudocode thread-safe ?

IList<T> dataList = SomeNhibernateRepository.GetData();

Parallel.For(..i..)
{
    foreach(var item in dataList)
    {
       DoSomething(item);
    }
}

The list never gets changed, it’s only iterated and read in parallel. No writing to fields or something like that whatsoever.

Thanks.

Answer 1

Yes, List<T> is fine to read from multiple threads concurrently, so long as nothing’s writing.

From the documentation:

A List<T> can support multiple readers concurrently, as long as the collection is not modified.

EDIT: Note that your code doesn’t necessarily use List<T> – just an IList<T>. Do you know the type returned by GetData()? If you’re in control of GetData() you probably want to document that the list returned by it is thread-safe for reading, if it’s actually returning a List<T>.