Ding ding ding!! Bingo. :-) See also Don't use unflock (flock 8). Ever. by merlyn.

It isn't a 100% valid concern anymore since 5.8 (or probably 5.7) and newer Perls make sure to flush and sync when unlocking, but you may still run on an older Perl (I write code for 5.6.1 and many people haven't gotten past 5.5 yet).

Makeshifts last the longest.