GATE CSE 1987 | Question: 1-xvi

Question

A critical region is

• A. One which is enclosed by a pair of $P$ and $V$ operations on semaphores.
• B. A program segment that has not been proved bug-free.
• C. A program segment that often causes unexpected system crashes.
• D. A program segment where shared resources are accessed.

Answer 1

A critical region is a program segment where shared resources are accessed, that's why we synchronize in the critical section.

PS: It is not necessary that we must use semaphore for critical section access (any other mechanism for mutual exclusion can also be used) and neither do sections enclosed by $P$ and $V$ operations are called critical sections.

Correct Answer : D.

Comments

If semaphores implies critical region and Semaphores always use PV then why isn’t option A right?

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Because critical regions are not always handled by semaphores, there are other ways too. So if instead of semaphores, we are using some other mechanism, then critical region won’t be enclosed by PV. So PV cannot be used to “define” critical regions – we have to follow the actual definition of critical regions.

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@niha42

instead of semaphores we can even mutexs for critical section acess