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ISRO | ISRO CS 2017 | Question 70

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A counting semaphore was initialized to 7. Then 20 P (wait) operations and x V (signal) operations were completed on this semaphore. If the final value of semaphore is 5, then the value x will be (A) 0 (B) 13 (C) 18 (D) 5

Answer: (C)

Explanation: In semaphores, P operation means wait operation and it decrements the value of the counting semaphore by 1 whereas V operation means signal operation and it increments the value of the counting semaphore.. Here a counting semaphore S = 7 After 20 P operations , s = 7-20 = -13 After ‘x’ V operations value of S=5, So -13 + xV = 5 and S = 18 . Option C is correct.

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Last Updated : 27 Oct, 2021
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