Question

In a certain application, the initial value of a counting semaphore s is 20. The following operations were completed on the semaphore in the 
   given order 5P, 20P, 2V, 15P, 5V, 10P, 1V. The new value of counting semaphore is  _____________ ? 


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Answer 1

Answer:-32

Explanation:

We all know that V operation increments or the semaphore value and P operation decrements value of semaphore. As this are counting semaphores then the the no of V or P operation done indicate the final value of semaphore. The no of V operations is multiplied by +1 or -1 depending upon increments and decrement hence we find final value

Here as the initial value is 20

After doing of the operations

5P=20-5= 15

20P=-15

2V=-13

15P=-28

5V=-23

10P=-33

1V=-32

Answer 2

The new value of counting semaphore is -22

Explanation:

In ‘semaphore’, ‘P means Wait’ and ‘V means Signal’. The ‘P (Wait)’ operation decreases the 'semaphore value by 1’ each time and ‘V (Signal)’ operation will increase the 'semaphore value by 1’ each time.

Here at a specific time of calculation, the value of counting ‘semaphore is 20’.

So,  20 - 5 - 20 + 2 - 15 + 5 - 10 + 1 = -22

Hence, the new value of counting 'semaphore' is -22

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