public function putUsingFileTimestamps($key, $value, array $filenames, $duration = null)
    {
        if (empty($duration))
            $duration = 0;

        $files = array();
        foreach ($filenames as $file) {
            $files[$file] = filemtime($file);
        }

        $timestamps = md5($files);

        // Populate all caches.
        $this->put($this->cacheKey($key), array('v' => $value, 't' => $timestamps), $duration);
//        $this->put($this->cachetskey($key), $timestamps, $duration);

        return true;
    }