GATE | GATE CS 2021 | Set 1 | Question 56

Consider the following pseudocode, where S is a semaphore initialized to 5 in line #2 and counter is a shared variable initialized to 0 in line #1. Assume that the increment operation in line #7 is not atomic.

1.  int counter =0;
2.  Semaphore S= init(5);
3.  void parop(void)
4.  {
5.        wait(S);
6.        wait(S);
7.        counter++;
8.        signal(S);
9.        signal(S);
10.  }

If five threads execute the function parop concurrently, which of the following program behavior(s) is/are possible?

(A)

The value of counter is 5 after all the threads successfully complete the execution of parop

(B)

The value of counter is 1 after all the threads successfully complete the execution of parop

(C)

The value of counter is 0 after all the threads successfully complete the execution of parop

(D)

There is a deadlock involving all the threads

Answer

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