I'm trying to copy hash record structures from a global shared hash to a local copy, so the threads won't have to lock the global all the time.

Basically, what you are trying to do is the completely wrong way to go about things when using iThreads with shared data.

Shared data is already copied to every thread that uses it. Making further copies is just dangerous, unnecessary, and impractical. You would still need to lock the shared data to copy it to your local copy, and again when you put it back. The costs in terms of both time and memory to create duplicate local copies of shared data totally outway any percieved benefit from avoiding locking.

If you modify your local copy on two threads, and then need to update the shared copy with the changes, you have no way to resolve the conflicts of merging the changes.

Considerable effort by some very clever people has gone into making sharing work. It was difficult for them to get it to the point where it is now pretty safe, transparent and usable. For you to try and replicate that in user-level Perl code is fraught with dangers and ultimately, a complete waste of time and effort.

In case that isn't clear :) Don't do that!