Under 1.5.2, this worked without a hitch. However, under 2.0, the same program tends to lock up on some computers. I'm not 100% sure (it's a bit hard to debug), but it looks like a global lock problem...

Any ideas? Is this supposed to work at all?

Can you post a short snippet demonstrating how exactly you initiate the DNS lookup, and how exactly you get the result back? I think it ought to work, and I'm not aware of a change that could cause it to break in 2.0. So far, in all cases where people reported "Tkinter and threading deadlocks", it turned out that the deadlock was in the application. Regards, Martin