In this day of multi-core CPUs and parallel programming platforms a common meme amongst developers has become “Is library X thread safe?”. As reasonable as that sounds, it’s actually not a particularly interesting question to ask, and anyone who claims to have a useful answer, probably doesn’t know what’s going on.
More importantly:
Phrases like “W is completely threadsafe” or “X isn’t thread safe” should be a red flag to you. They’re a sign that the speaker doesn’t quite understand the subtlety of the question, and the irrelevance of the answer without further qualification.