static <V> boolean casTabAt(Node<V>[] tab, int i,
                              Node<V> v) {
    try {
      return Unsafe.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, null, v);
    }
    catch (Throwable throwable) {
      throw new RuntimeException(throwable);
    }
  }
static <V> boolean casTabAt(Node<V>[] tab, int i,
                              Node<V> v)