Thanks for the input haukex. Making the change you suggested seems to have resolved my issue. My assumption was that the lock_type was a singular input- which I now know was incorrect. For various reasons, a database wouldn't work well for my situation, and I'm not worried about a first come first serve basis. For the simple code change, I used:

my $lock = new File::NFSLock ($datafile, LOCK_EX|LOCK_NB);