private static function rmdir_recursive($dir)
 {
     if (is_dir($dir)) {
         $objects = scandir($dir);
         foreach ($objects as $object) {
             if ($object != '.' && $object != '..') {
                 if (is_dir($dir . DIRECTORY_SEPARATOR . $object)) {
                     UploadCache::rmdir_recursive($dir . DIRECTORY_SEPARATOR . $object);
                 } else {
                     unlink($dir . DIRECTORY_SEPARATOR . $object);
                 }
             }
         }
         reset($objects);
         rmdir($dir);
     }
 }