My (limited) experience with perl threads suggests that creating threads is a quite expensive operation where you also have to be careful about the amount of objects that get copied from the parent to the new thread.

What I did to get around this issue is to use a very limited main thread (basically, only load the modules you want to use, if that), then start all the threads you're going to need (depending on usage, I use 1 worker thread for each CPU, but if your process is disk-bound you may want more)

Then possibly load more stuff into the main thread and do all communication between the main and worker threads using Thread::Queue, or a few other shared objects.

Trying to share a load of nested objects will probably result in a lot of overhead.

In any case: try to limit the number of threads you create and join - re-use as many as possible (i.e. all of them). That way, you can get quite stable memory usage.

update: also, you may want to get the latest stable perl (5.8.8), but at least you'll want the latest versions of threads and threads::shared from CPAN.