Thread Safe
Thread safe code can be safely called from multiple threads or concurrent tasks without causing any problems (data corruption, crashing, etc). Code that is not thread safe must only be run in one context at a time. An example of thread safe code is NSDictionary. You can use it from multiple threads at the same time without issue. On the other hand, NSMutableDictionary is not thread safe and should only be accessed from one thread at a time.
