use POSIX;
use File::lockf;
$status = File::lockf::lock ($args); # replace $args as appropriate.

if ($status) {
   # Uh oh, non zero value returned.
   # Lets use POSIX's errstr() to find out what happened
   $error_string = strerror ($status);
   die "Uh oh, lockf returned '$error_string'";
}