simple file locking schemehttp://search.cpan.org/perldoc?LockFile::Simple
This simple locking scheme is not based on any file locking system calls
such as 'flock()' or 'lockf()' but rather relies on basic file system
primitives and properties, such as the atomicity of the 'write()' system
call. It is not meant to be exempt from all race conditions, especially
over NFS. The algorithm used is described below in the *ALGORITHM* section.
It is possible to customize the locking operations to attempt locking once
every 5 seconds for 30 times, or delete stale locks (files that are deemed
too ancient) before attempting the locking.