I use flock to lock the file, so it should follow the semantics of 
flock(2).

http://www.perldoc.com/perl5.8.4/pod/func/flock.html

I don't really know what these semantics are, but I don't think deadlock 
should be possible. However, depending on the implementation there is a 
possibility of writer starvation, e.g. the exclusive lock is never granted 
because there is always at least one client reading the file. I'm, not too 
worried about that one though, it's nowhere near that heavily used.

Jonas