testbook

Question

A counting semaphore was initialized to 17. Then 8P (wait) operations and ‘n’V (signal) operations were completed on this semaphore. Find the value of n if total 14 down operations can be carried out successfully after 8 wait operation and n signal operations?

ans given 5

Comments

CS --> 17

Wait --> 8

then CS have $17-8 + n= 9 + n$

and now 14 down operations can be carried out successfully means after that cs=0 .... So, $9+n -14 = 0$

                      $n=5$

Correct me if i wrong

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is this line----after 8 wait operation and n signal operations is repeated in the question???

i was considering it a whole different equation and due to this it was creating a problem,, but after seeing the solution now im getting the point.

Answer 1

Initial Value of Semaphore:17

P operations:8

V operations:n

P operations decrease the value of the semaphore by 1 and V operations increase it by 1.

new value=17-P+V=14(then only 14 down can be carried ot successfully)

17-8+n=14

n=14-9=5