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GO Classes Test Series 2024 | Mock GATE | Test 11 | Question: 19

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Consider three concurrently executing threads in the same process using two semaphores $\text{s}1$ and $\text{s2}.$ Assume $\text{s1}$ has been initialized to $1$, while $\text{s2}$ has been initialized to $0.$ What are the possible values of the global variable $x,$ initialized to $0,$ after all three threads have terminated?

/* thread A */
P(s2); 
P(s1);
x = x*2; 
V(s1);

/* thread B */
P(s1); 
x = x*x; 
V(s1);

/* thread C */ 
P(s1); 
x = x+3; 
V(s2); 
V(s1);
  1. $6$
  2. $12$
  3. $18$
  4. $36$
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The possible sequences are $B,C,A (x = 6)$ or $C,A,B (x = 36)$ or $C,B,A (x = 18).$
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All possible values of the variable are:6,18,36.


The value 6 is possible by order:
T(B)->T(C)->T(A).


The value 18 is possible by order:

T(C)->T(B)->T(A).

The value 36 is possible by order:

T(C)->T(A)->T(B).

Since only thread B or thread C can occur initially due to P(s1), as s2 is initialized to 0

ANS:(A),(C),(D)

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