title: Is ConcurrentDictionary Keys or Values property threadsafe
body: <p>Have a question regarding thread safety with <code>ConcurrentDictionary</code>. From the API, I see that the enumerator is thread-safe, but I don't see the same for keys and values properties. My question is:</p>
  
  <p>Is it safe to loop over the <code>Keys</code> or <code>Values</code> collection when there are other threads modifying it concurrently?</p>