C# preventing Collection Was Modified exception

Question

Does

 foreach(T value in new List(oldList) )

is dangerous (costly) when oldList contains 1 millions of object T ?

More g

Answer 1

If you mean you can add/remove objects from another thread, I would: 1-synchronize the threads 2- in the add/remove threads, create a list of items to be added or deleted 3- and then delete these items in a critical section (so it is small - you don't have to synch while adding the items to the delete list)

If you dont want to do that, you can use for instead of foreach, that would avoid the exception, but you would have to take extra care so you do not get other kinds of exceptions