busy_wait_semaphore.c

typedef struct Mutex {
    int locked;
} Mutex;

typedef struct Semaphore {
    int count;
    Mutex mutex;
} Semaphore;


void mutex_init(Mutex *mut);
void mutex_lock(Mutex *mut);
void mutex_unlock(Mutex *mut);
void semaphore_init(Semaphore *sem, int value);
void semaphore_wait(Semaphore *sem);
void semaphore_signal(Semaphore *sem);
void shift(int *a, int *b);


int main() {
    Semaphore sem;
    semaphore_init(&sem, 1);
    return 0;
}

void semaphore_init(Semaphore *sem, int value) {
    mutex_init(&(sem->mutex));
    sem->count = value;
}

void semaphore_wait(Semaphore *sem) {
    
    int count = 0;
    while (count <= 0) {
        mutex_lock(&(sem->mutex));
        count = sem->count;
        mutex_unlock(&(sem->mutex));
    }
    
    mutex_lock(&sem->mutex);
    sem->count--;
    mutex_unlock(&sem->mutex);
}

void semaphore_signal(Semaphore *sem) {
    mutex_lock(&sem->mutex);
    sem->count++;
    mutex_unlock(&sem->mutex);
}

void mutex_init(Mutex *mut) {
    mut->locked = 0;
}

void mutex_lock(Mutex *mut) {
    int temp = 0;
    while (temp == 0) {
        shift(&(mut->locked), &temp);
    }
}

void mutex_unlock(Mutex *mut) {
    mut->locked = 1;
}

void shift(int *a, int *b) {
    *b = *a;
    *a = 0;
}