dotlock.py - example python script which uses dot-locking.

lock.sh - shell script example which uses dot-locking.
Can be used as a wrapper to invoke another program atomically.

Both of these are safe over NFS, and should be safe over SMB.

Also see lockfile, part of the procmail package and setlock,
part of djb's daemontools package.

See http://apenwarr.ca/log/?m=201012#13 for an excellent
writeup of the standard Unix locking APIs.