<T extends XdsResource> boolean unregister(XdsType type, String resourceName, ResourceWatcher<T> watcher) {
        if (!subscriberMap.containsKey(type)) {
            return false;
        }
        final Map<String, XdsStreamSubscriber<?>> resourceToSubscriber = subscriberMap.get(type);
        if (!resourceToSubscriber.containsKey(resourceName)) {
            return false;
        }
        //noinspection unchecked
        final XdsStreamSubscriber<T> subscriber =
                (XdsStreamSubscriber<T>) resourceToSubscriber.get(resourceName);
        subscriber.unregisterWatcher(watcher);
        if (subscriber.isEmpty()) {
            resourceToSubscriber.remove(resourceName);
            subscriber.close();
            if (resourceToSubscriber.isEmpty()) {
                subscriberMap.remove(type);
            }
            return true;
        }
        return false;
    }
Returns {@code true} if a subscriber is removed.
xds/src/main/java/com/linecorp/armeria/xds/SubscriberStorage.java