@Override
    public Set<String> call() throws Exception {
        HashSet<String> result = new HashSet<String>(parameter);
        Iterator<String> iter = result.iterator();
        while (iter.hasNext()) {
            String p = iter.next();
            OfflinePlayer player = server.getOfflinePlayer(p);

            if (player.isOnline()) {
                iter.remove();
            } else {
                if (player.getLastPlayed() < cutoff) {
                    // Keep in list
                } else {
                    iter.remove();
                }
            }
        }
        return result;
    }