/**
  * 创建ElexConfig的实例
  * @param $config_file
  * @param $options
  * @return ElexConfig
  */
 public static function getInstance($config_file, $options = null)
 {
     if (!self::$instance instanceof self) {
         self::$use_apc_cache = function_exists('apc_fetch');
         // 验证配置文件路径的正确性
         self::checkConfigPath($config_file);
         // 先尝试从缓存中反序列化
         self::$instance = self::getConfigFromCache($config_file);
         if (empty(self::$instance)) {
             // 创建一个新的ElexConfig对象
             self::$instance = new self($config_file, $options);
             // 将对象序列化后写入缓存
             self::writeConfigToCache($config_file, self::$instance);
         }
     }
     return self::$instance;
 }