IEnumerable thread safety?

Question

I have a main thread that populates a List. Further I create a chain of objects that will execute on different threads, requiring access to the List. The

Answer 1

In other words if the original list is guaranteed not be written to, is it safe for multiple threads to use .Where or foreach on the IEnumerable?

Yes it's only a problem if the list gets mutated.

But note than IEnumerable can be cast back to a list and then modified.

But there is another alternative: wrap your list into a ReadOnlyCollection and pass that around. If you now throw away the original list you basically created a new immutable list.