Question

If I have a

Dictionary<int, StreamReader> myDic = new Dictionary<int, StreamReader>
//Populate dictionary

One thread does

myDic[0] = new StreamReader(path);

Another thread does

myDic[1] = new StreamReader(otherpath)

Is this thread safe because the actual item in the dictionary getting modified is different to the one on the other thread or will I get a InvalidOperationException: Collection was modified

Answer 1

You will only get InvalidOperationException: Collection was modified if you enumerate the dictionary while modifying.

However, that is not thread-safe.
If one of those operations causes the dictionary to resize, the other one may get lost.
Instead, use ConcurrentDictionary.