And finding thread-safe resolver libraries has been a problem.  At
a  previous job, we just one thread that handled all the resolver
stuff and if other threads had to wait for that, so be it.

The world could use a BSD licensed threaded resolver library.

Quoting Nathan J. Williams (nathanw@wasabisystems.com):
> Daniel Carosone <dan@geek.com.au> writes:
> 
> > I think it's something to do with the resolver - is the present
> > one properly thread-safe?
> 
> >From a quick look, the present resolver isn't thread-safe at all. Lots
> of global state, no locks.
> 
>         - Nathan