Apache Reference: mod_rewrite, RewriteLock
Rewrite Engine Mutual Exclusion Lock
Syntax: RewriteLock A
Example: RewriteLock logs/rewrite_lock
Since: Apache 1.3
This directive sets the file name for a synchronization mutual exclusion lock file that mod_rewrite needs to communicate with RewriteMap programs. Set file to a local path (not on a NFS-mounted device) when you want to use a rewriting map program. This directive is not required for other types of rewriting maps.