but this sounds ineffiecient to me.

What would you do?

Semaphores, yes. My decision would proceed as:

1. Don't do this at all: I don't need such multiprocessing.
2. Have pipes for each child, with a protocol wherein children may request tasks and the parent may supply them with tasks. As long as I'm writing a protocol, it may as well also carry feedback from the tasks.
3. Use POE instead.
4. Use (not Perl:) Erlang instead.
5. Fail, colour the problem as insurmountable and backtrack within my overarching design.