在WordPress插件中读取此cookie有什么问题？

In the code below, running at the 'init' action via a WordPress Plugin, the cookie isn't being read. ( !isset([...]) is evaluating to true. ) I've checked my cookies, and the cookie is set properly. Any idea what's happening?

if ( !isset( $_COOKIE[get_site_url().'_has_visited'] ) ) {
    setcookie( get_site_url().'_has_visited', 1, time()+86400, COOKIEPATH, COOKIE_DOMAIN, false);
    do_stuff();
}