当会话 ID 已知但无法启动会话时删除会话变量

i could kill the cart before going to paypal but what if they wanted to go back and change things? i could kill the cart on the landing page, but what if they get to a different page somehow? i would really like to destroy the cart but not the entire session right when i get payment confirmation but i am not sure how. i have tried this on my ipn page:

session_start();

$a = session_id();

mail("webmaster@mysite.com", "ipn session id 0", $a, "From: webmaster@mysite.com");

//results in blank email, unlike in other locations on actual displayed pages

// Unset all of the session variables.

$_SESSION = array();

// Delete the session cookie to kill the session

if (isset($_COOKIE[session_name()])) {

setcookie(session_name(), '', time()-42000, '/');

}

// Finally, destroy the session.

session_destroy();

unset($_SESSION['cart']);

unset($_SESSION['product_id_array']);

unset($_SESSION['pp_checkout_btn']);

unset($_SESSION['state']);

unset($_SESSION['total']);

unset($_SESSION['shipping']);

unset($_SESSION['grand_total']);

但是当我返回查看购物车页面时，它仍然存在.任何想法将不胜感激.任何有帮助的具体代码，请告诉我，我会发布.