Part of the point of separate processes is that they cannot access each other's memory. So no matter how you pass \$lock to a different process, it won't be able to do anything useful with it.

You need to use flock (or something similar) but on a different file for each user and this filename is what you pass to each subprocess, not \$lock. I'd use File::Temp to create these lock files safely.

Update: The original node says:

flock() is not an option for this, as this program will need to be able to be run by multiple users at the same time.

hence my suggestion and why I don't think merlyn's reply is in context.