Path::Class::File::Lockable uses simple files to indicate
whether a file is locked or not.

It does not use flock(), since that is unstable over NFS.
Effort has been made to avoid race conditions.

Path::Class::File::Lockable is intended for long-standing locks,
as in a Subversion workspace. See SVN::Class for example.

WWW: http://search.cpan.org/dist/Path-Class-File-Lockable/