C#基礎-FileStream實現多線程斷點續傳

一、前言

       網上有許多的多線程斷點續傳操作，但總是寫的很雲里霧里，或者寫的比較坑長。由於這幾個月要負責公司的在線升級項目，所以正好順便寫了一下

       代碼如下：

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";  //本地目標文件路徑

            FileInfo SeverFilePath = new FileInfo(@"E:\Test\TestFile\Server\1.msi"); //服務器待文件路徑
            long FileLength = SeverFilePath.Length; //待下載文件大小


            Console.WriteLine("Start Configuration");
            int PackCount = 0;  //初始化數據包個數

            long PackSize = 1024000; //數據包大小

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

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


            Console.WriteLine("Start Recieve");
            var tasks = new Task[PackCount];  //多線程任務

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


                int Threadindex = index; //這步很關鍵，在Task()里的絕對不能直接使用index
                var task = new Task(() =>
                {
                    string tempfilepath = @"E:\Test\TestFile\Temp\" + "QS_" + Threadindex + "_" + PackCount; //臨時文件路徑

                    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); //等待所有線程完成
            Console.WriteLine("Recieve End");


            //檢測有哪些數據包未下載
            Console.WriteLine("Start Compare");
            DirectoryInfo TempDir = new DirectoryInfo(@"E:\Test\TestFile\temp"); //臨時文件夾路徑
            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());
                }
            }

            //最后補上這些缺失的文件
            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");


            //准備將臨時文件融合並寫到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");



            //刪除臨時文件
            Console.WriteLine("Start Delete Temp Files");
            foreach (FileInfo Tempfile in TempDir.GetFiles())
            {
                Tempfile.Delete();
            }
            Console.WriteLine("Delete Success");
            Console.ReadKey();
        }


        //這個方法可以放到Remoting或者WCF服務中去，然后本地調用該方法即可實現多線程斷點續傳
        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、討論      

1）需要注意的是第44行，不能直接使用index變量在Task()里進行操作，而是要將它賦給Threadindex，讓Threadindex在Task()里，不然會直接報錯，為什么呢？

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

2）70至108行代碼可以在外面再套一層while循環，循環檢測臨時文件是否下完整了，然后再定義一個檢測最大上限，超過這個上限就放棄本次更新，當用戶的網絡恢復正常后下次再做更新操作。所以說放臨時文件的文件夾最好要包含版本信息，不會把2.0.0的臨時文件和1.0.0的臨時文件搞混。

3） FileStream.Position 與 FileStream.Seek(long offset, SeekOrigin seekorigin) 的作用都是獲取流的指針位置，當文件路徑使用絕對路徑時使用Position；相對路徑時使用Seek方法

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