A certain computation generates two arrays a and b such that a[i]=f(i) for 0 ≤ i < n and b[i]=g(a[i]) for 0 ≤ 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: Process Y: private i; private i; for (i=0; i < n; i++) { for (i=0; i < n; i++) { a[i] = f(i); EntryY(R, S); ExitX(R, S); b[i]=g(a[i]); } } Which one of the following represents the CORRECT implementations of ExitX and EntryY? (A) ExitX(R, S) { P(R); V(S); } EntryY (R, S) { P(S); V(R); } (B) ExitX(R, S) { V(R); V(S); } EntryY(R, S) { P(R); P(S); } (C) ExitX(R, S) { P(S); V(R); } EntryY(R, S) { V(S); P(R); } (D) ExitX(R, S) { V(R); P(S); } EntryY(R, S) { V(S); P(R); }

Computer Science Gate CS-2013 in Computer Science 11 months ago

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