Each of a set of n processes executes the following code using two semaphores…

GATE · 2020 · CS · Computer Science & IT

Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P.

CODE SECTION P

Each process executes its own CODE SECTION P before the synchronization code below.

wait(a);
count = count + 1;
if (count == n) signal(b);
signal(a);
wait(b);
signal(b);

CODE SECTION Q

Each process begins its own CODE SECTION Q only after completing the synchronization code above.

What does the code achieve?

  1. A.

    It ensures that no process executes CODE SECTION Q before every process has finished CODE SECTION P.

  2. B.

    It ensures that at most two processes are in CODE SECTION Q at any time.

  3. C.

    It ensures that all processes execute CODE SECTION P mutually exclusively.

  4. D.

    It ensures that at most n−1 processes are in CODE SECTION P at any time.

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Correct answer: A

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