## Question:

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);
}``````