phpcms中的模型问题

下面是phpcms的其中两个模型

<?php
defined('IN_PHPCMS') or exit('No permission resources.');
pc_base::load_sys_class('model', '', 0);
class cache_model extends model {
	public function __construct() {
		$this->db_config = pc_base::load_config('database');
		$this->db_setting = 'default';
		$this->table_name = 'cache';
		parent::__construct();
	}
}
?>

<?php
defined('IN_PHPCMS') or exit('No permission resources.');
pc_base::load_sys_class('model', '', 0);
class block_model extends model {
	public function __construct() {
		$this->db_config = pc_base::load_config('database');
		$this->db_setting = 'default';
		$this->table_name = 'block';
		parent::__construct();
	}
}
?>

其中共同的代码是

pc_base::load_sys_class('model', '', 0);

本来以为这里会载入两次，当我去看pc_base类才发现并非这样，而是使用一个静态数组记录加载过的对象和类

public static function load_sys_class($classname, $path = '', $initialize = 1) {
	return self::_load_class($classname, $path, $initialize);
}

private static function _load_class($classname, $path = '', $initialize = 1) {
		static $classes = array();
		if (empty($path)) $path = 'libs'.DIRECTORY_SEPARATOR.'classes';

		$key = md5($path.$classname);
		if (isset($classes[$key])) {
			if (!empty($classes[$key])) {
				return $classes[$key];
			} else {
				return true;
			}
		}
		if (file_exists(PC_PATH.$path.DIRECTORY_SEPARATOR.$classname.'.class.php')) {
			include PC_PATH.$path.DIRECTORY_SEPARATOR.$classname.'.class.php';
			$name = $classname;
			if ($my_path = self::my_path(PC_PATH.$path.DIRECTORY_SEPARATOR.$classname.'.class.php')) {
				include $my_path;
				$name = 'MY_'.$classname;
			}
			if ($initialize) {
				$classes[$key] = new $name;
			} else {
				$classes[$key] = true;
			}
			return $classes[$key];
		} else {
			return false;
		}
	}