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 * = &(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?
(A) The implementation may not work if context switching is disabled in P
(B) Instead of using fetch-and —set, a pair of normal load/store can be used
(C) The implementation of V is wrong
(D) The code does not implement a binary semaphore
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