in reply to Efficient shared memory - possible? how??
You could make a tied hash, which will store its values in shared memory. Beaware though that when you initiate a piece of shared memory, you will have to supply a size. If you're sticking to storing numerical values, then it's easy. 4 or 8 bytes will do. If you want to share strings, and have them mutable as in Perl, you will have to implement your own double pointer trick (as Perl does).
Optimizing memory is hard work if your choice of tool is Perl, because Perl usually picks speed over memory when having a choice, and because there's a lot of hidden stuff going on around your back.
Using threads make it easier to share variables, but Perl threads copy a priory every variable that isn't shared, unlike (Unix) forks which uses copy-on-write. Threads may be the better solution for you, but that's something only you can find out, but doing actual measurement.