code: public synchronized boolean addInvalidationListener(InvalidationListener listener) {
          if (bEnableListener && listener != null) {
              eventSource.addListener(listener);
              if (tc.isDebugEnabled()) {
                  Tr.debug(tc, "addInvalidationListener() cacheName=" + this.cacheName + " listener=" + eventSource.getInvalidationListenerCount());
              }
              return true;
          }
          return false;
      }
docs: This is a helper method to add invalidation listener to all entries.