Question

我正在使用Dropbox中的文件在服务器之间进行通信。过了一会儿，我意识到在Dropbox内的文件上执行时，每隔一段时间基本File操作就会出现延迟。

我需要的是这样的事情：

public class MyFile
{
    const int maxWaitCount = 60;
    //..
    /// <summary>
    /// remove file - also has to work inside Dropbox directory
    /// </summary>
    /// <returns>0 for ok or error code</returns>
    public int rm()
    {
        string name = Os.winInternal(FullName);
        if (File.Exists(name))
        {
            File.Delete(name);
            #region double check if file is gone
            if (Ensure)
                return awaitFileVanishing(name);
            #endregion
        }
        return 0;
    }
    //..
    private int awaitFileMaterializing(string fileName) //..
    private int awaitFileVanishing(string fileName) //..
    /// <summary>
    /// Constructor: auto-ensure mode for file systems that do not synchronously wait for the end of an IO operation i.e. Dropbox
    /// </summary>
    /// <remarks>only use the ensure mode if it has to be guaranteed that the IO operation was completely done
    /// when the method call returns; necessary e.g. for Dropbox directories since (currently) Dropbox first updates the
    /// file in the invisible . folder and then asynchronously updates the visible file and all the remote copies of it</remarks>
    /// <param name="filename"></param>
    public MyFile(string filename)
    {
        Ensure = filename.ToLower().Contains("dropbox");
        // ..
    }
}

由于我需要一个快速的解决方案，我想出了一个我正在回答我自己的问题的答案。但是，我很容易想象你们中的一些人也有这个问题，并找到了一个不同的，可能更具说服力的解决方案。请告诉我。

Answer 1

这是awaitFileMaterializing和awaitFileVanishing的当前解决方案，用作MyFile的一部分。

    private int awaitFileMaterializing(string fileName)
    {
        int count = 0;
        bool exists = false;
        while (count < maxWaitCount)
        {
            try
            {
                exists = File.Exists(fileName);
            }
            catch (Exception) { }   // device not ready exception if Win 2003
            if (exists)
                break;
            Thread.Sleep(5);
            count++;
        }
        if (count >= maxWaitCount)
            throw new FileNotFoundException("ensure failed - timeout.", fileName);
        return -count;
    }
    private int awaitFileVanishing(string fileName)
    {
        int count = 0;
        bool exists = true;
        while (count < maxWaitCount)
        {
            try
            {
                exists = File.Exists(fileName);
            }
            catch (Exception) { }   // device not ready exception if Win 2003
            if (!exists)
                break;
            Thread.Sleep(5);
            count++;
        }
        if (count >= maxWaitCount)
            throw new IOException("ensure failed - timeout in deleting " + fileName + ".");
        return -count;
    }

Answer 2

您可以创建FileSystemWatcher来监控您的Dropbox文件夹。 FileSystemWatcher有一个已删除的事件，您可以附加到该事件，告诉您何时从正在监视的文件夹中删除文件。

MSDN Source & Examples

如何确保删除后Dropbox中的文件真的消失了？

2 个答案: