Semaphores S and T. The code for the processes P and Q is shown below.…

2004

Semaphores S and T. The code for the processes P and Q is shown below. Synchronization statements can be inserted only at points W, X, Y, and Z. Which of the following will always lead to an output starting with '001100110011'?

Process P

Process Q

While(true)

While(true)

{

{

W:

Y:

print '0';

print '1';

print '0';

print '1';

X:

Z:

}

}

Answer: B. P(S) at W, V(T) at X, P(T) at Y, V(S) at Z, S initially 1, and T initially 0 — Initialize semaphores S=1 and T=0. Insert V(T) at point X to release Process Q after Process P prints the first '0'. Insert V(S) at point Z to allow Process P…

  1. A.

    P(S) at W, V(S) at X, P(T) at Y, V(T) at Z, S and T initially 1

  2. B.

    P(S) at W, V(T) at X, P(T) at Y, V(S) at Z, S initially 1, and T initially 0

  3. C.

    P(S) at W, V(T) at X, P(T) at Y, V(S) at Z, S and T initially 1

  4. D.

    P(S) at W, V(S) at X, P(T) at Y, V(T) at Z, S initially 1, and T initially 0

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Correct answer: B

Initialize semaphores S=1 and T=0. Insert V(T) at point X to release Process Q after Process P prints the first '0'. Insert V(S) at point Z to allow Process P to resume after Process Q prints the second '1'. This configuration ensures the sequence 0, 0, 1, 1 repeats indefinitely.

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