threads has been broken up until 5.8 (maybe I got the exact version wrong). It was broken so badly that I've seen warnings not to use it in earlier versions.

In newer versions, however, it works very nicely - never had any problems with it in a complex multi-threaded application.

BTW, I think that the adjective "broken" is used in our world not necessarily for "has a bug". Sometimes it's referred to "not behaving as one would expect".