c# - System.IO.File.Copy() 产生 System.IO.IOException : The specified network name is no longer available

Question

我有一个 Windows 服务 (C# .Net 3.5)，它从网络共享获取数据并将其复制到服务的主机。

复制的数据大小从50KB到750MB不等，复制的文件数量也不同。在大约 20% 的副本中，我收到 System.IO.IOException: 指定的网络名称不再可用。

我的 google-fu 未能找到有关在 File.Copy 期间可能导致此问题的原因的答案。以前有人见过/解决过这个问题吗？

这是执行复制的递归方法。异常发生在 File.Copy(fromFile, toFile, overwrite);

行上

private static int RecursiveCopyDirectory(string from, string to, bool merge, bool overwrite, int depth)
    {
        depth++;

        if (!from.EndsWith(Path.DirectorySeparatorChar.ToString()))
        {
            to += Path.DirectorySeparatorChar;
        }
        if (!to.EndsWith(Path.DirectorySeparatorChar.ToString()))
        {
            to += Path.DirectorySeparatorChar;
        }

        System.Diagnostics.Debug.WriteLine(string.Format("RecursiveDirectoryCopy( {0}, {1}, {2} )", from, to, merge));
        if (Directory.Exists(to))
        {
            if (!merge)
            {
                return (int)EventEnum.FileSystemError_DirectoryAlreadyExists;
            }
        }
        else
        {
            Directory.CreateDirectory(to);
        }

        string[] directories = Directory.GetDirectories(from);

        foreach (string fromDirectory in directories)
        {
            string [] fromDirectoryComponents = fromDirectory.Split(Path.DirectorySeparatorChar);
            string toDirectory = to + fromDirectoryComponents[fromDirectoryComponents.Length - 1];
            RecursiveCopyDirectory(fromDirectory, toDirectory, merge, overwrite, depth);
        }

        string[] files = Directory.GetFiles(from);

        foreach (string fromFile in files)
        {
            string fileName = Path.GetFileName(fromFile);
            //System.Diagnostics.Debug.WriteLine(string.Format("Name: {0}", to + fileName));    
            string toFile = to + fileName;

            File.Copy(fromFile, toFile, overwrite);
        }

        return (int)EventEnum.GeneralSuccess;
    }

Answer 1

File.Copy() 打开下划线流。当 File.Copy() 正在进行时，您可能失去了连接。因此，它无法刷新并关闭流。

解决此问题的一种可能方法是使用 FileStream 类并发生此类异常时调用Win32 API CloseHandle，这样做会释放操作系统文件句柄，以便您可以重新打开该文件。

[ DllImport("Kernel32") ]
public static extern bool CloseHandle(IntPtr handle);

FileStream fs;
try {
...
}

catch(IOException)
{
// If resource no longer available, or unable to write to.....
if(...)
CloseHandle(fs.Handle);
}

此外，MSDN recommends not to rely on overwrite 。 尝试删除现有文件并在复制时创建新文件。

File.Copy(..., ..., TRUE) does not work properly.

Be very careful with this method, as the Overwrite = True does NOT work properly.

I had an existing destination file that had some information inside it that was somehow preserved and carried over to the source file that was supposed to copy over it.  This should be impossible, but I confirmed it for myself.