Multiple choice

The atomic fetch-and-set x, y instruction unconditionally sets the memory location x to 1 and fetches the old value of x n y without allowing any intervening access to the memory location x. consider the following implementation of P and V functions on a binary semaphore S. void P (binary_semaphore *s) { unsigned y; unsigned *x = &(s->value); do { fetch-and-set x, y; } while (y); } void V (binary_semaphore *s) { S ->value = 0; } Which one of the following is true? ( Which one of the following is true?

  1. The implementation may not work if context switching is disabled in P

  2. Instead of using fetch-and -set, a pair of normal load/store can be used

  3. The implementation of V is wrong

  4. The code does not implement a binary semaphore
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A Correct answer
Explanation

If there are more than two processes and context & switching processes is disabled in P then this implementation doesn't work properly and can't synchronize the processes.

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