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At a particular time of computation, the value of a counting semaphore is $7$. Then $20$ $P$ operations and $15$ $V$ operations were completed on this semaphore. The resulting value of the semaphore is :

1. $42$
2. $2$
3. $7$
4. $12$

Why Semaphore Wait and Signal Operation Denoted by P and V respectively, specially in ISRO Paper.

@pankajbelwal P and V were the terminology used by Dijkstra when he proposed this algorithm.

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Currently semaphore is $7$ so, after $20$ $P$(wait) operation it will come to $-13$ then for $15$ V(signal) operation the value comes to $2.$

### 1 comment

I think it will be -13

because currently semaphore is 7so, after 20 P(wait or down) operation it will come to −13 (7-20)

and then after 15 V( signal or up) we have 15+(-13) = 2

Option B

since P(S) decreases the counting semaphore value

The initial value of semaphore is 7

After finishing 20 P operations S=-13 (i.e 7-20 =-13)

Now S=-13

V(S) increases the counting semaphore value

After finishing 15 V operations S=-13+15=2

Therefore Answer is 2 option B

### 1 comment

which one is correct?what will be the value after 20 p operations ?

S = 7 - 20 =-13(in suspended list)

S= -13+15 = 2

The resulting value of the semaphore is : 2 option b

suspended list
13

Current Value of Counting Semaphore : 7

20 P operation, value = 7-20 = -13

15 V operation, values = -13+15 = 2

by