multiple processes with private working dirs

[Tim Arnold]

I have a bunch of processes to run and each one needs its own working 
directory. I'd also like to know when all of the processes are finished.

(1) First thought was threads, until I saw that os.chdir was process-global.
(2) Next thought was fork, but I don't know how to signal when each child is 
finished.
(3) Current thought is to break the process from a method into a external 
script; call the script in separate threads.  This is the only way I can see 
to give each process a separate dir (external process fixes that), and I can 
find out when each process is finished (thread fixes that).

Am I missing something? Is there a better way? I hate to rewrite this method 
as a script since I've got a lot of object metadata that I'll have to 
regenerate with each call of the script.

thanks for any suggestions,
--Tim Arnold