【WordPress】サイト更新日をキーとして重い処理をキャッシュする

function get_my_site_cache( $key , $callback , $arg ){
	$key_date = '_my_site_cache_date_' . $key . '_';
	$key_value = '_my_site_cache_value_' . $key . '_';
	$last_modified = get_lastpostmodified('gmt');
	
	if( get_option($key_date) === $last_modified){
		$result =  get_option($key_value);
		if( false !== $result) return  $result;
	}

	$result = call_user_func($callback, $arg);
	update_option($key_date, $last_modified, false);
	update_option($key_value ,$result, false);

	return $result;
}

// キャッシュからデータを取得して最新記事リスト(liタグ)を取得
function get_new_entry_list( $page_num = 5 ){
	$entries = get_my_site_cache( 'my_new_entry_list' , 'create_new_entry_data' , $page_num );
	
	$count = 1;
	$result = '';
	$url = $name = '';
	
	foreach($entries as $e){
        switch( $count ){
            case 1:$url = esc_url($e);break;
            case 2:$name = esc_html($e);break;
            case 3:
                $result .=  '<li><a href="'.$url.'">'
                            . $name .'</a>('.esc_html($e) . ')</li>';
                $count = 0;
        }
        $count ++;
    }
    return $result;
} 
// キャッシュ無効時のデータ生成
function create_new_entry_data( $page_num ){
	$args = array(
        'posts_per_page' => $pageNum
    );
    $result = [];
    $posts = get_posts( $args );
    foreach ( $posts as $post ){
        $result[] = get_permalink( $post->ID );
		$result[] = $post->post_title;
		$result[] = $post->post_modified;
    }
    return $result;
}

class My_Newpost_Widget extends WP_Widget {
    function __construct() {
        
        parent::__construct('My_Newpost_Widget', 'My最新記事','My最新記事' );
    }

    public function widget( $args, $instance ){
        echo $args['before_widget']
                .$args['before_title'] . '最新記事' . $args['after_title']
                .'<ul id="new_entry">'
                .get_new_entry_list(5).'</ul>'
                .$args['after_widget'];
    }

    public function form( $instance ) {
    }

    public function update( $new_instance, $old_instance ) {
        return $new_instance;
    }
}
add_action( 'widgets_init', function(){
    register_widget('My_Newpost_Widget');
} );