Module Lock_file

Mutual exclusion between processes using flock and lockf. A file is considered locked if either of these mechanisms works.

These locks are OS-level but are Local (will not work across computers even if they mount the same directory).


val create : ?message:string -> ?close_on_exec:bool -> ?unlink_on_exit:bool -> string -> bool

create ?close_on_exec ?message path tries to create a file at path containing the text message, which defaults to the pid of the locking process. It returns true on success, false on failure. Note: there is no way to release the lock or the fd created inside! It will only be released when the process dies. If close_on_exec is false, then the lock will not be released until children created via fork and exec also terminate. If not specified, close_on_exec=true. Note that by default, the lock file is not cleaned up for you when the process exits. If you pass unlink_on_exit:true, an at_exit handler will be set up to remove the lock-file on program termination.

The lock file is created with mode 664, so will not be world-writable even with umask 0.

val create_exn : ?message:string -> ?close_on_exec:bool -> ?unlink_on_exit:bool -> string -> unit

create_exn ?message path is like create except that it throws an exception on failure instead of returning a boolean value

val blocking_create : ?timeout:Time.Span.t -> ?message:string -> ?close_on_exec:bool -> ?unlink_on_exit:bool -> string -> unit

blocking_create t tries to create the lock. If another process holds the lock this function will wait until it is released or until timeout expires.

val is_locked : string -> bool

is_locked path returns true when the file at path exists and is locked, false otherwise. Requires write permission for the lock file.

val get_pid : string -> Core_kernel.Std.Pid.t option

get_pid path reads the lock file at path and returns the pid in the file. Returns None if the file cannot be read, or if the file contains a message that is not an int.

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).