LEO: But Bob, there is some file locking.

Centralized revision control systems solve this problem in one of two different "source management models": file locking and version merging.

The local filesystem handles file locking as messages are added, moved and deleted.

Metadata controller, which manages file locking, space allocation and data access authorization in a storage area network (SAN)

The kernel or libraries of a system could be modified to disable the file locking, without making this apparent to the program.

A similar problem can occur when two or more users simultaneously edit the same file in a revision control system that does not have file locking.

In the case of files, the sticky-bit may be used by the system to indicate the style of file locking to be performed.

Exclusion control between processes is performed when connecting to a database by file locking.

Database maintenance uses file locking, whereby it can serialize access to the entire physical file underlying a database.

Everything you never wanted to know about file locking, a review of the Unix file locking options and their problems (dated December 13, 2010)