})
      @Override
      void reachabilityFence(@Nullable Object o) {
        if (IS_REACHABILITY_FENCE_METHOD_USABLE) {
          Reference.reachabilityFence(o);
        }
      }
    },
    /** No-op implementation used under J2ObjC (if ClosingFuture even has J2ObjC users). */
    NO_OP_CALLER {
      @Override
      void reachabilityFence(@Nullable Object o) {}
    };