Is List<T> thread-safe for reading?

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>.