I think that thread variables are unshared by default and thus your use of File::Find and $File::Find::name should still work. But I haven't used threads, so I can't really tell you.

While searching for something else, I came across acme's journal entry where he mentions Proc::ParallelLoop, which does fork subprocesses to work on loops in parallel. As you do the output directly from your threads and Proc::ParallelLoop seems even to buffer the output from the threads, you could be able to directly use that module. I haven't used it though.