Is this non-locked TryGetValue() dictionary access thread-safe?

Question

private object lockObj = new object();

private Dictionary dict = new Dictionary();

public string GetOrAddFromDict(int key)
{
         


        

Answer 1

Question a: Is it thread-safe? If yes, why?

Not only is it not thread safe; it will also throw with NullReferenceException if accessed while another thread is reorganizing the hash buckets. The lock statement is wicked fast, don't avoid it.

Question b: How is this double-TryGetValue() pattern called?

It's called a 'bug' by most people ;)