package Sem;

sub new {
    my $class = shift(@_);
    use Carp ();
    my $filespec = shift(@_) || Carp::croak("What filespec?");
    open my $fh, ">", $filespec or Carp::croak("Can't open semaphore file $filespec: $!");
    chmod 0666, $filespec; # assuming you want it a+rw
    use Fcntl 'LOCK_EX';
    flock $fh, LOCK_EX;
    return bless {'fh' => $fh}, ref($class) || $class;
}

sub unlock {
    close(delete $_[0]{'fh'} or return 0);
    return 1;
}

1;