public void ParallelDownloader()
        {
            var downloader = new HttpClientDownloader();

            Parallel.For(0, 3, new ParallelOptions
            {
                MaxDegreeOfParallelism = 3
            }, i =>
            {
                var d = downloader.Clone();
                downloader.Download(new Request("http://www.163.com"));
            });
        }