daedlocks and threads operating system

Question

Suppose we want to synchronize two concurrent process P and Q using binary semaphore S and T.

Process P:                        Process Q:

     while(1){                            while(1){

        W:                               Y:

          print ‘0’;                          print ‘1’;

          print ‘0’;                          print ‘1’;

        X:                               Z:

    }

Synchronization statements can be inserted only at points W,X,Y,Z. Which of the following can lead to an output starting with ‘00110011’ ?

a. W : P(S)  X : V(S)  Y : P(T)  Z: V(T) and initially S = T= 1

b. W : P(S)  X : V(T)  Y : P(T)  Z: V(S) and initially S = 1 and T= 0

c. W : P(S)  X : V(T)  Y : P(T)  Z: V(S) and initially S = T= 1

d. W : P(S)  X : V(S)  Y : P(T)  Z: V(T) and initially S = 1 and T= 0

Comments

Option B

Answer 1

To ensure that the given output is printed we need to take values as S=1 and T=0.
To ensure that it prints only (0011)* only, we need to take W: P(S), X:V(T) not X:V(S) as it leads to printing 0000……
Also, Y:P(T) and Z:V(S) such that 00 can be printed only after 11 is printed.
Therefore, answer is option b.