Update: Incase it is unclear, this post refers ONLY to the situation when using ithreads.

(Though it's also worth remembering that under Win32, fork is emulated using ithreads under the covers.)

It's worth noting that unless you intend using a module in multiple threads, there is little point in loading that module prior to spawning your threads. It only consumes extra memory.

If you do need to use a module in multiple threads, remember that you cannot call methods across threads, or share objects. That is to say, if you create an object in one thread, and share it with another thread and then try to invoke methods upon the object in the second thread, it won't do what you want it to.

It is almost always better to require the modules needed by a thread, from within that thread, once it has started.