Concurrent Queues

typedef struct __node_t {
  int value;
  struct __node_t *next;
} node_t;
typedef struct __queue_t {
  node_t *head;
  node_t *tail;
  pthread_mutex_t head_lock, tail_lock;
}
void Queue_Init(queue_t *q) {
  node_t *tmp = malloc(sizeof(node_t));
  tmp->next = NULL;
  q->head = q->tail = tmp;
  pthread_mutex_init(&q->head_lock, NULL);
  pthread_mutex_init(&q->tail_lock, NULL);
}
void Queue_Enqueue(queue_t *q, int value) {
  node_t *tmp = malloc(sizeof(node_t));
  assert(tmp != NULL);
  tmp->value = value;
  tmp->next  = NULL;
  pthread_mutex_lock(&q->tail_lock);
  q->tail->next = tmp;
  q->tail = tmp;
  pthread_mutex_unlock(&q->tail_lock);
}
int Queue_Dequeue(queue_t *q, int *value) {
  pthread_mutex_lock(&q->head_lock);
  node_t *tmp = q->head;
  node_t *new_head = tmp->next;
  if (new_head == NULL) {
      pthread_mutex_unlock(&q->head_lock);
      return -1; // queue was empty
  }
  *value = new_head->value;
  q->head = new_head;
  pthread_mutex_unlock(&q->head_lock);
  free(tmp);
  return 0;
}