No, you misunderstand. It's not that the interface isn't threadsafe. It's that the implementation is single-threaded. That is, no matter how many threads are making name lookup requests, there'll only be one actually in-flight at any one time. Having 50 threads making simultaneous name lookups will get you 1 thread doing a name lookup and 49 threads waiting their turn to issue the name lookup.
in reply to Re^2: Using Threading to speed up DNS Resolution
in thread Using Threading to speed up DNS Resolution