use Gimp;
use Fcntl ':flock';

my ( $lockfile, $lock_fh );

Gimp::initialized() or Gimp::init() or Gimp::initialized() or die "failed connecting to gimp server";

$lockfile = '/tmp/gimplock-' . Gimp->server_eval( q[$$] ); # append the Perl-Server pid to the lockfile name, in case you have multiple Perl-Servers

{
    no warnings 'redefine';
    *Gimp::lock = sub {
        open( $lock_fh, ">>$lockfile" )
          or die "failed opening lockfile '$lockfile' for appending: $!";
        return flock( $lock_fh, LOCK_EX );
    };
    *Gimp::yield = *Gimp::lock{CODE};

    *Gimp::unlock = sub {
        flock( $lock_fh, LOCK_UN );
    };
}


Gimp::lock();

# ... do something with gimp ...

Gimp::yield(); # give somebody else a turn

# ... do something else with gimp ...

Gimp::unlock();