C# 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 = 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:\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, 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:\Test\TestFile\temp"); //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:\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, 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:\Test\TestFile\Server\1.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？查看链接

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，查看链接

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