Operating-Systems

Question 43

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 the above

Operating-SystemsProcess-SynchronizationGATE 1997

Question 43 Explanation:

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.

Correct Answer: D

Question 43 Explanation:

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.

Operating-Systems

Nielit Scientist-B CS 4-12-2016

Operating-Systems

Nielit Scientist-B CS 4-12-2016

Operating-Systems