code: public void addEntityListener(String repoFullName, EntityListener entityListener) {
      lock.writeLock().lock();
      try {
        verifyRepoRegistered(repoFullName);
        SetMultimap<Object, EntityListener> entityListeners =
            this.entityListenersByRepo.get(repoFullName);
        entityListeners.put(entityListener.getEntityId(), entityListener);
      } finally {
        lock.writeLock().unlock();
      }
    }
docs: Adds an entity listener for a entity of the given class that listens to entity changes
  
  @param entityListener entity listener for a entity