topic – RBR

Semaphores

Please wait while the activity loads.
If this activity does not load, try refreshing your browser. Also, this page requires javascript. Please visit using a browser with javascript enabled.

If loading fails, click here to try again

Question 1

Given below is a program which when executed spawns two concurrent processes : semaphore X : = 0 ; /* Process now forks into concurrent processes P1 & P2 */

P1	P2
repeat forever V (X) ; Compute ; P(X) ;	repeat forever P(X) ; Compute ; V(X) ;

Consider the following statements about processes P1 and P2:

It is possible for process P1 to starve.
It is possible for process P2 to starve.

Which of the following holds?

A	Both 1 and 2 are true
B	1 is true but 2 is false
C	2 is true but 1 is false
D	Both 1 and 2 are false

Operating-Systems Semaphores Gate 2005-IT

Question 1 Explanation:

P1 can be starves on P, then P2 loops forever.
P2 can be starves on P, then P1 loops forever.
Both statements (i) and (ii) are True.

Question 2

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:

A	42
B	2
C	7
D	12

Operating-Systems Semaphores Gate-1992

Question 2 Explanation:

Let the semaphore be S.
Initial value of S is 7.
So after 20P operations and 15V operations the value of semaphore S will be,
S = 7-20+15 = 2

There are 2 questions to complete.