关于文件的切割下载

public class Program
    {
        public static CountdownEvent cde = new CountdownEvent(0);

        //每个线程下载的字节数，方便最后合并
        public static ConcurrentDictionary<long, byte[]> dic = new ConcurrentDictionary<long, byte[]>();

        //请求文件
        public static string url = "http://www.pncity.net/bbs/data/attachment/forum/201107/30/1901108yyd8gnrs2isadrr.jpg";

        static void Main(string[] args)
        {
            for (int i = 0; i < 5; i++)
            {
                Console.WriteLine("\n****************************\n第{0}次比较\n****************************", (i + 1));

                //不用线程
                //RunSingle();

                //使用多线程
                RunMultiTask();
            }

            Console.Read();
        }

        static void RunMultiTask()
        {
            Stopwatch watch = Stopwatch.StartNew();

            //开5个线程
            int threadCount = 5;

            long start = 0;

            long end = 0;

            var total = GetSourceHead();

            if (total == 0)
                return;

            var pageSize = (int)Math.Ceiling((Double)total / threadCount);

           // cde.Reset(threadCount);

            Task[] tasks = new Task[threadCount];

            for (int i = 0; i < threadCount; i++)
            {
                start = i * pageSize;

                end = (i + 1) * pageSize - 1;

                if (end > total)
                    end = total;

                var obj = start + "|" + end;

                tasks[i] = Task.Factory.StartNew(j => new DownFile().DownTaskMulti(obj), obj);
            }

            Task.WaitAll(tasks);

            var targetFile = "C://down//" + url.Substring(url.LastIndexOf('/') + 1);

            FileStream fs = new FileStream(targetFile, FileMode.Create);

            var result = dic.Keys.OrderBy(i => i).ToList();

            foreach (var item in result)
            {
                fs.Write(dic[item], 0, dic[item].Length);
            }

            fs.Close();

            watch.Stop();

            Console.WriteLine("多线程：下载耗费时间:{0}", watch.Elapsed);
        }

        static void RunSingle()
        {
            Stopwatch watch = Stopwatch.StartNew();

            if (GetSourceHead() == 0)
                return;

            var request = (HttpWebRequest)HttpWebRequest.Create(url);

            var response = (HttpWebResponse)request.GetResponse();

            var stream = response.GetResponseStream();

            var outStream = new MemoryStream();

            var bytes = new byte[10240];

            int count = 0;

            while ((count = stream.Read(bytes, 0, bytes.Length)) != 0)
            {
                outStream.Write(bytes, 0, count);
            }

            var targetFile = "C://down//" + url.Substring(url.LastIndexOf('/') + 1);

            FileStream fs = new FileStream(targetFile, FileMode.Create);

            fs.Write(outStream.ToArray(), 0, (int)outStream.Length);

            outStream.Close();

            response.Close();

            fs.Close();

            watch.Stop();

            Console.WriteLine("不用线程：下载耗费时间:{0}", watch.Elapsed);
        }

        //获取头信息
        public static long GetSourceHead()
        {
            var request = (HttpWebRequest)HttpWebRequest.Create(url);

            request.Method = "Head";
            request.Timeout = 3000;

            var response = (HttpWebResponse)request.GetResponse();

            var code = response.StatusCode;

            if (code != HttpStatusCode.OK)
            {
                Console.WriteLine("下载的资源无效！");
                return 0;
            }

            var total = response.ContentLength;

            Console.WriteLine("当前资源大小为:" + total);

            response.Close();

            return total;
        }
    }

    public class DownFile
    {
        // 多线程下载
        public void DownTaskMulti(object obj)
        {
            var single = obj.ToString().Split('|');

            long start = Convert.ToInt64(single.FirstOrDefault());

            long end = Convert.ToInt64(single.LastOrDefault());

            var request = (HttpWebRequest)HttpWebRequest.Create(Program.url);

            request.AddRange(start, end);

            var response = (HttpWebResponse)request.GetResponse();

            var stream = response.GetResponseStream();

            var outStream = new MemoryStream();

            var bytes = new byte[10240];

            int count = 0;

            while ((count = stream.Read(bytes, 0, bytes.Length)) != 0)
            {
                outStream.Write(bytes, 0, count);
            }

            outStream.Close();

            response.Close();

            Program.dic.TryAdd(start, outStream.ToArray());

           // Program.cde.Signal();
        }
    }