Gate CS-2013 Question Paper With Solutions

Q. 39 A certain computation generates two arrays a and b such that a[i]=f(i)
for 0 < i < n and b6i @ = g^a6i @h for 0 # i 1 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);
}

Answer: (c)

Explanation:

Gate CS-2013 Question Paper With Solutions

Learn More:   Gate ME-2006 Question Paper With Solutions

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