Semaphores

// need to delete the stack

1) Restroom problem using semaphores:

int women_active;
int men_active;
int women_waiting;
int men_waiting;

semaphore women_waiting_sem{0};
semaphore men_waiting_sem{0};

semaphore mutex{1};

// list<semaphore*> men_waiting;

void woman_wants_to_enter(){
	mutex.down();

	if(men_active) {
		women_waiting++;
		mutex.up();
		women_waiting_sem.down();
		mutex.down();
	} else {
		women_active++;
	}

	mutex.up();
}

void woman_leaves(){
	mutex.down();

	women_active--;

	if(!women_active){
		while(men_waiting--) {
			men_waiting_sem.up();
			men_active++;
		}
	}

	mutex.up();
}

2) Barrier Synchronization

const auto N{42}; // numRunners

semaphore numReady{0};
semaphore staerted{0};

void starter() {
	for (i = 0; i < N; i++)
		numReady.down();
	
	for (i = 0; i < N; i++)
		started.up();
}

void runner() {
	numReady.up();
	started.down();
}