let rename oldFile newFile =

begin try System.link oldFile newFile with Unix.Unix_error _ -> () end;

let res = try (System.stat oldFile).Unix.LargeFile.st_nlink = 2

with Unix.Unix_error _ -> false

in

System.unlink oldFile;

res

let flags = [Unix.O_WRONLY; Unix.O_CREAT; Unix.O_EXCL]

let create name mode =

try

Unix.close (System.openfile name flags mode);

true

with Unix.Unix_error (Unix.EEXIST, _, _) ->

false

let rec unique name i mode =

let nm = name ^ (string_of_int i) in

if create nm mode then nm else

(* highly unlikely *)

unique name (i + 1) mode

let acquire name =

Util.convertUnixErrorsToTransient

"Lock.acquire"

(fun () ->

match Sys.unix with

| true -> (* O_EXCL is broken under NFS... *)

rename (unique name (Unix.getpid ()) 0o600) name

| _ ->

create name 0o600)

let release name = try System.unlink name with Unix.Unix_error _ -> ()

let is_locked name =

Util.convertUnixErrorsToTransient

"Lock.test"

(fun () -> System.file_exists name)