Module Lock_file.Nfs

module Nfs: sig .. end
An implementation neutral NFS lock file scheme that relies on the atomicity of link over NFS (see NFS Illustrated, atomicity for more information). Rather than relying on a working traditional advisory lock system over NFS we create a hard link between the file given to the create call and a new file <filename>.nfs_lock. This link call is atomic (in that it succeeds or fails) across all systems that have the same filesystem mounted. The link file must be cleaned up on program exit (normally accomplished by an at_exit handler, but see caveats below).

There are a few caveats compared to local file locks:



val create : ?message:string -> string -> bool
lock ?message path tries to create and lock the file at path by creating a hard link to path.nfs_lock. The contents of path will be replaced with message, which will be the caller's hostname:pid by default.

Efforts will be made to release this lock when the calling program exits. But there is no guarantee that this will occur under some types of program crash

val create_exn : ?message:string -> string -> unit
create_exn ?message path like create, but throws an exception when it fails to obtain the lock
val blocking_create : ?message:string -> string -> unit
blocking_create ?message path like create, but sleeps for 1 second between lock attempts and does not return until it succeeds
val critical_section : ?message:string -> string -> f:(unit -> 'a) -> 'a
critical_section ?message path ~f wrap function f (including exceptions escaping it) by first locking (using Lock_file.Nfs.create_exn) and then unlocking the given lock file.
val get_hostname_and_pid : string -> (string * int) option
get_hostname_and_pid path reads the lock file at path and returns the hostname and path in the file if it can be parsed.