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GATE Computer Science (CS) 2013 Solved Paper

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Question : 49

Total: 65

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 computesthe 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?

ExitX(R, S) {
P(R);
V(S);
}
EntryY(R, S) {
P(S);
V(R);
}
ExitX(R, S) {
      V(R);
      V(S);
}
EntryY(R, S) {
         P(R);
          P(S);
}
ExitX(R, S) {
        P(S);
        V(R);
}
EntryY(R, S) {
          V(S);
          P(R);
}
ExitX(R, S) {
        V(R);
        P(S);
}
EntryY(R, S) {
         V(S);
         P(R);
}

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