Test by Bikram | Mock GATE | Test 3 | Question: 48

Question

The following five concurrent processes operate on counting semaphore variable $\left ( S \right )$, which is initialized to $0$.

• P1 : wait$\left ( s \right )$ ;     $cs$ ;     signal$\left ( s \right )$ ;
• P2 : wait$\left ( s \right )$ ;     $cs$ ;     signal $\left ( s \right )$ ;
• P3 : wait$\left ( s \right )$ ;     $cs$ ;     signal $\left ( s \right )$ ;
• P4 : signal$\left ( s \right )$ ;  $cs$ ;     wait $\left ( s \right )$ ;
• P5 : signal$\left ( s \right )$ ;  $cs$ ;     wait $\left ( s \right )$;

The maximum possible value of $S$ is ______.

Comments

@Utkarsh Joshi

Maximum value of S asked at the end of execution of program or in between ??

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Maximum value at any time be it at the end or in between

Answer 1

The maximum possible value S is 2 (when P4 and P5 enter the critical section) ,

the rest processes decrement S before entering CS  and later increments it after completion of CS. 

Thus the overall value never goes beyond 2.

Comments

Should it also be mentioned where this value is maximum?