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？

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，

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。