Implementing semaphore by using mutex operations and primitives

Question

Some time ago had an interview and was asked to implement Semaphore by using mutex operations and primitives only (he allowed int to be considered as atomic). I came with soluti

Answer 1

as @chill pointet out, the solution I did write down here will not work, as locks have unique ownership. I guess in the end you will revert to busy wait (if you are not allowed to use condition variables). I leave it here if ppl. have the same idea they see that this DOES NOT WORK ;)

struct Semaphore {
int size;
atomic count;
mutex protection;
mutex wait;

Semaphore(int n) : size(n) { count.store(0); }

void aquire() {
    protection.lock();
    --count;
    if (count < -1) {
        protection.unlock();
        wait.lock();
    }
    protection.unlock();
}

void release() {
    protection.lock();
    ++count;
    if (count > 0) {
        wait.unlock();
    }
    protection.unlock();
}
};