GATE | GATE CS 2013 | Question 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 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);
}
(A) A
(B) B
(C) C
(D) D
Answer: (C)
Explanation:
The purpose here is neither the deadlock should occur
nor the binary semaphores be assigned value greater
than one.
A leads to deadlock
B can increase value of semaphores b/w 1 to n
D may increase the value of semaphore R and S to
2 in some cases
See https://www.geeksforgeeks.org/operating-systems-process-management-question-13/
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Last Updated :
28 Jun, 2021
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