ISRO2016-45

Question

At a particular time of computation the value of a counting semaphore is 7. Then 20 $P$ operations and $x$ $V$ operations were completed on this semaphore. If the new value of semaphore is $5$, $x$ will be 

• A. 18
• B. 22
• C. 15
• D. 13

Answer 1

Each P operation decreases the value of counting semaphore by 1  and each V operation increases the value of counting semaphores by 1

Here given value of counting semaphore  is 7  then 20 p operation will reduces it to -13

then in order to increase it to 5    18 V operations are needed

hence x=18 ans is A

Answer 2

Here,P represents Wait and V represents Signal. P operation decrements the semaphore value by 1 every time and V operation will increments the semaphore value by 1 every time.

At a particular time of computation the value of a counting semaphore is 7.After that 20 P and x V operations were completed on the semaphore.

So,

7 - 20 + x =5

-13 +x=5
 

x=18

Answer 3

hope it might help u......

Comments

In case the value of P becomes less than equal to 0 then no operation is performed right?