private function cancel($id)
    {
        // Cannot cancel if it has been processed.
        if (!isset($this->handles[$id])) {
            return false;
        }

        $handle = $this->handles[$id]['easy']->handle;
        unset($this->delays[$id], $this->handles[$id]);
        curl_multi_remove_handle($this->_mh, $handle);
        curl_close($handle);

        return true;
    }