public function purge() {
        if ($this->isready) {
            $files = glob($this->glob_keys_pattern(), GLOB_MARK | GLOB_NOSORT);
            if (is_array($files)) {
                foreach ($files as $filename) {
                    @unlink($filename);
                }
            }
            $this->keys = array();
        }
        return true;
    }