code: private void deliverCacheUpdate(SlotReference slot, MetadataCache cache) {
          for (final MetadataCacheListener listener : getCacheListeners()) {
              try {
                  if (cache == null) {
                      listener.cacheDetached(slot);
                  } else {
                      listener.cacheAttached(slot, cache);
                  }
              } catch (Throwable t) {
                  logger.warn("Problem delivering metadata cache update to listener", t);
              }
          }
      }
docs: Send a metadata cache update announcement to all registered listeners.
  
  @param slot the media slot whose cache status has changed
  @param cache the cache which has been attached, or, if {@code null}, the previous cache has been detached