Concurrent Linked Lists

// basic node structure
typedef struct __node_t{
  int key;
  struct __node_t *next;
} node_t;
// basic list structure (one used per list)
typedef struct __list_t{
  node_t *head; 
  pthread_mutex_t lock;
} list_t;
void List_Init(list_t *L) {
    L->head = NULL;
    pthread_mutex_init(&L->lock, NULL);
}
int List_Insert(list_t *L, int key) {
  pthread_mutex_lock(&L->lock);
  node_t *new = malloc(sizeof(node_t));
  if (new == NULL) {
      perror("malloc");
      pthread_mutex_unlock(&L->lock);
      return -1; // fail
  }
  new->key  = key;
  new->next = L->head;
  L->head   = new;
  pthread_mutex_unlock(&L->lock);
  return 0; // success
}
int List_Lookup(list_t *L, int key) {
  pthread_mutex_lock(&L->lock);
  node_t *curr = L->head;
  while (curr) {
    if (curr->key == key) {
      pthread_mutex_unlock(&L->lock);
      return 0; // success
    }
    curr = curr->next;
  }
  pthread_mutex_unlock(&L->lock);
  return -1; // failure
}