c# - FileSystemWatcher 丢失文件

Question

我是 c# 的新手，正在编写一个程序，该程序将使用从名为 folderWatch 的方法调用的 fileSystemWatcher 来监视文件夹中的 .xml 文件。 .xml 文件包含一个电子邮件地址和一个图像路径，一旦阅读，图像就会通过电子邮件发送。如果我一次只添加几个 xml，我的代码可以正常工作，但是当我尝试将大量 xml 转储到文件夹 fileSystemWatcher 时，它不会处理所有这些。请帮我指明正确的方向。

private System.IO.FileSystemWatcher m_Watcher;
public string folderMonitorPath = Properties.Settings.Default.monitorFolder;

    public void folderWatch()
    {
        if(folderMonitorPath != "")
        {
            m_Watcher = new System.IO.FileSystemWatcher();
            m_Watcher.Filter = "*.xml*";
            m_Watcher.Path = folderMonitorPath;
            m_Watcher.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite
                                     | NotifyFilters.FileName | NotifyFilters.DirectoryName;
            m_Watcher.Created += new FileSystemEventHandler(OnChanged);
            m_Watcher.EnableRaisingEvents = true;
        }
    }

    public void OnChanged(object sender, FileSystemEventArgs e)
    {
        displayText("File Added " + e.FullPath);
        xmlRead(e.FullPath);
    }

读取xml

    public void xmlRead(string path)
    {

        XDocument document = XDocument.Load(path);
        var photo_information = from r in document.Descendants("photo_information")
                                select new
                                {
                                    user_data = r.Element("user_data").Value,
                                    photos = r.Element("photos").Element("photo").Value,
                                };
        foreach (var r in photo_information)
        {
            if (r.user_data != "")
            {
                var attachmentFilename = folderMonitorPath + @"\" + r.photos;
                displayText("new user data " + r.user_data);
                displayText("attemting to send mail");
                sendemail(r.user_data, attachmentFilename);
            }
            else
            {
                displayText("no user data moving to next file");
            }
        }

发送邮件

public void sendemail(string email, string attachmentFilename)
    {
        //myTimer.Stop();

            MailMessage mail = new MailMessage();
            SmtpClient SmtpServer = new SmtpClient(smtpClient);

            mail.From = new MailAddress(mailFrom);
            mail.To.Add(email);
            mail.Subject = "test";
            mail.Body = "text";

            SmtpServer.Port = smtpPort;
        SmtpServer.Credentials = new System.Net.NetworkCredential("username", "password");
        SmtpServer.EnableSsl = true;
        // SmtpServer.UseDefaultCredentials = true;

        if (attachmentFilename != null)
            {
                Attachment attachment = new Attachment(attachmentFilename, MediaTypeNames.Application.Octet);
                ContentDisposition disposition = attachment.ContentDisposition;
                disposition.CreationDate = File.GetCreationTime(attachmentFilename);
                disposition.ModificationDate = File.GetLastWriteTime(attachmentFilename);
                disposition.ReadDate = File.GetLastAccessTime(attachmentFilename);
                disposition.FileName = Path.GetFileName(attachmentFilename);
                disposition.Size = new FileInfo(attachmentFilename).Length;
                disposition.DispositionType = DispositionTypeNames.Attachment;
                mail.Attachments.Add(attachment);
            }
        try
        {
            SmtpServer.Send(mail);
            displayText("mail sent");
        }
        catch (Exception ex)
        {
           displayText(ex.Message);

        }

    }

Answer 1

首先，FileSystemWatcher 有内部限制 buffer存储未决通知。根据文档:

The system notifies the component of file changes, and it stores those changes in a buffer the component creates and passes to the APIs. Each event can use up to 16 bytes of memory, not including the file name. If there are many changes in a short time, the buffer can overflow. This causes the component to lose track of changes in the directory

您可以通过将 InternalBufferSize 设置为 64 * 1024(64KB，最大允许值)来增加该缓冲区。

接下来(也许更重要)是如何清除此缓冲区。您的 OnChanged 处理程序被调用，并且仅当它完成时 - 通知从该缓冲区中删除。这意味着如果您在处理程序中做了很多工作 - 缓冲区溢出的可能性要高得多。为避免这种情况 - 在 OnChanged 处理程序中尽可能少地工作，并在单独的线程中完成所有繁重的工作，例如(不是生产就绪代码，仅用于说明目的):

var queue = new BlockingCollection<string>(new ConcurrentQueue<string>());
new Thread(() => {
    foreach (var item in queue.GetConsumingEnumerable()) {
        // do heavy stuff with item
    }
}) {
    IsBackground = true
}.Start();
var w = new FileSystemWatcher();
// other stuff
w.Changed += (sender, args) =>
{
    // takes no time, so overflow chance is drastically reduced
    queue.Add(args.FullPath);
};

您也没有订阅 FileSystemWatcher 的 Error 事件，因此您不知道何时(以及是否)出现问题。