in reply to A flock()alypse now
This should work fine for a single file. Semaphores are required for multiple file locking of course, but that was covered above. By openning the file twice with different filehandles you're just getting a different file descriptor to work with. flock locks files, not file descriptors. Even using system calls dup and fork just cause multiple references to the same lock.
In Section
Seekers of Perl Wisdom