A system has n$+1$ servers S$,$ S$1,$ S$2,...,$ Sn$,$ but only S is visible to the clients. Sever S allows up to $50$ clients to connect to it$,$ but performs no actual computations. It forwards the computation request to one of the n computation servers. Each computation server runs its own compute$()$ method to process data and return a result object. Because the result will be further processed by different objects in parallel, it is desirable to let these objects all see the same result regardless whether one has manipulated the result before the others. Which design pattern is not very useful?