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GATE Computer Science (CS) 2021 Shift 1 Solved Paper

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Question : 56

Total: 65

Consider the following pseudocode, where S is a semaphore intialized to 5 in line#2 an counter is a shared variable intialized 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?

There is a deadlock involving all the threads.
The value of counter is 5 after all the threads successfully complete the execution of parop.
The value of counter is 1 after all the threads successfully complete the execution of parop.
The value of counter is 0 after all the threads successfully complete the execution of parop.

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