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:\Test\TestFile\Local\1.msi";  //本地目标文件路径

             FileInfo SeverFilePath = new FileInfo(@"E:\Test\TestFile\Server\1.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 = ;  //初始化数据包个数

             long PackSize = ; //数据包大小

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

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

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

             for (int index = ; 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:\Test\TestFile\Temp\" + "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, , 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:\Test\TestFile\temp"); //临时文件夹路径
             List<string> Comparefiles = new List<string>();

             for (int i = ; i < PackCount; i++)
             {
                 bool hasfile = false;
                 foreach (FileInfo Tempfile in TempDir.GetFiles())
                 {
                     if (Tempfile.Name.Split('_')[] == 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 > )
             {
                 foreach (string com_index in Comparefiles)
                 {
                     string tempfilepath = @"E:\Test\TestFile\Temp\" + "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, , 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, , Convert.ToInt32(onefileLength));
                         writestream.Write(buffer, , 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:\Test\TestFile\Server\1.msi";
             using (FileStream ServerStream = new FileStream(SeverFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite, *, true))
             {
                 byte[] buffer = new byte[length];
                 ServerStream.Position = start;
                 //ServerStream.Seek(start, SeekOrigin.Begin);
                 ServerStream.Read(buffer, , 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