I agree with your NFS/flock point. That could still go wrong if there were to be an NFS system (or a Windows machine for that matter).

(My 'initial version' was just something that looked like the code I used. I might have forgotten to log the actual error message there, but I wasn't coding 'literal' there.)

But apart from that and your localised filehandle, your code looks very much like mine, with just some inverted logical structures.