private void update() {
        int upd = mirror.updates();
        if (generation != upd) {
            generation = upd;
            recipients.clear();
            List<Mirror.Entry> arr = mirror.lookup(pattern);
            for (Mirror.Entry entry : arr) {
                recipients.add(Hop.parse(entry.getSpecString() + session));
            }
        }
    }
Updates the list of matching recipients by querying the extern slobrok.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/ExternPolicy.java