Q39

A certain computation generates two arrays a and b such that $a[i] = f(i)$ for $0 \leq i < n$ and $b[i] = g(a[i])$ for $0 \leq i < n$. Suppose this computation is decomposed into two concurrent processes $X$ and $Y$ such that $X$ computes the array $a$ and $Y$ computes the array $b$. The processes employ two binary semaphores $R$ and $S$, both initialized to zero. The array $a$ is shared by the two processes. The structures of the processes are shown below. Process X: private i; for (i=0; i< n; i++) { a[i] = f(i); ExitX(R, S); } Process Y: private i; for (i=0; i< n; i++) { EntryY(R, S); b[i] = g(a[i]); } Which one of the following represents the CORRECT implementations of ExitX and EntryY?