in reply to IPC::Sharable ... curious ipcs -a results
1) Yes. The semaphore is set up at the same time as the shared memory segment.
2) Yes. What happens with IPC::Shareable is that in nested data structures, the nested data isn't stored in the initially created shared memory segment. Only the initial variable is. Each new element is contained within its own new segment.
Disclaimer: I'm a co-maintainer of the distribution in question.