C#基础-FileStream实现多线程断点续传

一、前言

       网上有许多的多线程断点续传操作，但总是写的很云里雾里，或者写的比较坑长。由于这几个月要负责公司的在线升级项目，所以正好顺便写了一下

       代码如下：

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading.Tasks;

namespace TestCenter
{
    class Program
    {
        static void Main(string[] args)
        {
            string LocalSavePath = @"E:TestTestFileLocal1.msi";  //本地目标文件路径

            FileInfo SeverFilePath = new FileInfo(@"E:TestTestFileServer1.msi"); //服务器待文件路径
            long FileLength = SeverFilePath.Length; //待下载文件大小


            Console.WriteLine("Start Configuration");
            int PackCount = 0;  //初始化数据包个数

            long PackSize = 1024000; //数据包大小

            if (FileLength % PackSize > 0)
            {
                PackCount = (int)(FileLength / PackSize) + 1;
            }

            else
            {
                PackCount = (int)(FileLength / PackSize);
            }


            Console.WriteLine("Start Recieve");
            var tasks = new Task[PackCount];  //多线程任务

            for (int index = 0; index < PackCount; index++)
            {


                int Threadindex = index; //这步很关键，在Task()里的绝对不能直接使用index
                var task = new Task(() =>
                {
                    string tempfilepath = @"E:TestTestFileTemp" + "QS_" + Threadindex + "_" + PackCount; //临时文件路径

                    using (FileStream tempstream = new FileStream(tempfilepath, FileMode.Create, FileAccess.Write, FileShare.Write))
                    {
                        int length = (int)Math.Min(PackSize, FileLength - Threadindex * PackSize);

                        var bytes = GetFile(Threadindex*PackCount, length);

                        tempstream.Write(bytes, 0, length);
                        tempstream.Flush();
                        tempstream.Close();
                        tempstream.Dispose();
                    }
                });
                tasks[Threadindex] = task;
                task.Start();
            }

            Task.WaitAll(tasks); //等待所有线程完成
            Console.WriteLine("Recieve End");


            //检测有哪些数据包未下载
            Console.WriteLine("Start Compare");
            DirectoryInfo TempDir = new DirectoryInfo(@"E:TestTestFile	emp"); //临时文件夹路径
            List<string> Comparefiles = new List<string>();

            for (int i = 0; i < PackCount; i++)
            {
                bool hasfile = false;
                foreach (FileInfo Tempfile in TempDir.GetFiles())
                {
                    if (Tempfile.Name.Split('_')[1] == i.ToString())
                    {
                        hasfile = true;
                        break;
                    }
                }
                if (hasfile == false)
                {
                    Comparefiles.Add(i.ToString());
                }
            }

            //最后补上这些缺失的文件
            if (Comparefiles.Count > 0)
            {
                foreach (string com_index in Comparefiles)
                {
                    string tempfilepath = @"E:TestTestFileTemp" + "QS_" + com_index+ "_" + PackCount;
                    using (FileStream Compstream = new FileStream(tempfilepath, FileMode.Create, FileAccess.Write, FileShare.Write))
                    {
                        int length = (int)Math.Min(PackSize, FileLength - Convert.ToInt32(com_index) * PackSize);
                        var bytes = GetFile(Convert.ToInt32(com_index)*PackCount, length);
                        Compstream.Write(bytes, 0, length);
                        Compstream.Flush();
                        Compstream.Close();
                        Compstream.Dispose();
                    }
                }

            }
            Console.WriteLine("Compare End");


            //准备将临时文件融合并写到1.msi中
            Console.WriteLine("Start Write");
            using (FileStream writestream = new FileStream(LocalSavePath, FileMode.Create, FileAccess.Write, FileShare.Write))
            {
                foreach (FileInfo Tempfile in TempDir.GetFiles())
                {
                    using (FileStream readTempStream = new FileStream(Tempfile.FullName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
                    {
                        long onefileLength = Tempfile.Length;
                        byte[] buffer = new byte[Convert.ToInt32(onefileLength)];
                        readTempStream.Read(buffer, 0, Convert.ToInt32(onefileLength));
                        writestream.Write(buffer, 0, Convert.ToInt32(onefileLength));
                    }
                }
                writestream.Flush();
                writestream.Close();
                writestream.Dispose();
            }
            Console.WriteLine("Write End");



            //删除临时文件
            Console.WriteLine("Start Delete Temp Files");
            foreach (FileInfo Tempfile in TempDir.GetFiles())
            {
                Tempfile.Delete();
            }
            Console.WriteLine("Delete Success");
            Console.ReadKey();
        }


        //这个方法可以放到Remoting或者WCF服务中去，然后本地调用该方法即可实现多线程断点续传
        public static byte[] GetFile(int start, int length)
        {
            string SeverFilePath = @"E:TestTestFileServer1.msi";
            using (FileStream ServerStream = new FileStream(SeverFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite, 1024*80, true))
            {
                byte[] buffer = new byte[length];
                ServerStream.Position = start;
                //ServerStream.Seek(start, SeekOrigin.Begin);
                ServerStream.Read(buffer, 0, length);
                return buffer;
            }
        }
    }
}

二、讨论      

1）需要注意的是第44行，不能直接使用index变量在Task()里进行操作，而是要将它赋给Threadindex，让Threadindex在Task()里，不然会直接报错，为什么呢？

链接：http://bbs.csdn.net/topics/390769774

2）70至108行代码可以在外面再套一层while循环，循环检测临时文件是否下完整了，然后再定义一个检测最大上限，超过这个上限就放弃本次更新，当用户的网络恢复正常后下次再做更新操作。所以说放临时文件的文件夹最好要包含版本信息，不会把2.0.0的临时文件和1.0.0的临时文件搞混。

3） FileStream.Position 与 FileStream.Seek(long offset, SeekOrigin seekorigin) 的作用都是获取流的指针位置，当文件路径使用绝对路径时使用Position；相对路径时使用Seek方法

链接：https://stackoverflow.com/questions/7238929/stream-seek0-seekorigin-begin-or-position-0