code: public void removeListener(InvalidationListener listener) {
          synchronized (hsInvalidationListeners) {
              hsInvalidationListeners.remove(listener);
              invalidationListenerCount = hsInvalidationListeners.size();
              bUpdateInvalidationListener = true;
          }
      }
docs: This removes a specified listener for Invalidation listener. If it was not already registered
  then this call is ignored.
  @param listener The listener to be removed.