GATE - 1997 | OS | Each Process Pi, i= 1…….9 is coded as follows

GATE - 1997 [Operating System]

Question:

Each Process P_i, i= 1…….9 is coded as follows

 repeat 
    P(mutex)
    {Critical section}
    V(mutex)
 forever

The code for P₁₀ is identical except it uses V(mutex) in place of P(mutex). What is the largest number of processes that can be inside the critical section at any moment?
(A) 1
(B) 2
(C) 3
(D) None of above

Solution:

Option (D) is Correct.

Since the both code (i.e., P₁ to P₉ and P₁₀) can be executed any number of times and code for P₁₀ is
repeat
{
V(mutex)
C.S.
V(mutex)
}
forever
Now, let me say P₁ is in CS then P₁ is in CS
then P₁₀ comes and executes CS (upon mutex).
Now, P₂ comes (down on mutex).
Now P₁₀ moves out of CS (again binary semaphore will be 1).
Now P₃ comes (down on mutex).
Now P₁₀ comes (upon mutex).
Now P₄ comes (down mutex).
⁞ So, if we take P₁₀ 'in' and 'out' of CS recursively, all 10 processes can be in CS at same time using binary semaphore only.

 

Thank You