WordPress save_post无法访问帖子ID

Question

add_action('save_post', 'gmc_save_recipe', 10, 2);

function gmc_save_recipe($post_id, $post) {
  //exit($post_id); //blank page
  //$id = get_the_ID();
  //exit($id); //blank page
  //exit(print_r($post)); //WP_Post Object ( [ID] => 288....
  //exit($post->ID //blank page
}

有谁能告诉我为什么我会在所有这些场景中返回空白页面？我希望它能显示帖子ID。