Semaphores

Question

If two processes R₁ and R₂ accessing the shared variables A and B protected by two binary semaphores S_A and S_B respectively, both initialized to 1.
R and Q denote the usual semaphore operators, where R decrements the semaphore value, and Q increments the semaphore value. The pseudo code of R₁ and R₂ is as follows:

R1:

while(True){
    do{
        k1:____;
        k2:____;
        a = a+1;
        b = b-1;
        R(SA);
        R(SB);
    }
}

R2:

while(True){ 
    do{
        k3:____;
        k4:____;
        a = a+1;
        b = b-1; 
        R(SB);
        R(SA);
    }
}

The options are :

• R(S_B ),R(S_A ),R(S_A ),R(S_B )
• R(S_B ),R(S_A ),R(S_B ),R(SA )
• R(S_A ),R(S_B ),R(S_A ),R(S_B )
• R(S_A ),R(S_B ),R(S_B ),R(S_A )
• None of the above

Comments

1st and 3rd option results in deadlock

2nd and 4th can lead to Starvation

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There is no signal operation in the above transaction .. How semaphore value turn=1 to execute another process.. ?

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 R decrements the semaphore value, and Q increments the semaphore value

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there is no Q operation in the given transactions ?

Correct  me if i am wrong

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oh yeah how did i missed that :o

there is something wrong with the question or answer is none of the above