等待文件存在

Question

我已经用WebApi2编写了一组web服务，它们最终调用一个CMD程序，该程序启动一个XML客户端，传递一个格式化的OpenEdge字符串，然后通过调用一个.p过程将记录插入到OpenEdge Progress数据库中(WebSpeed不是一个选项)。

.P文件有一组针对Progress应用程序运行的业务逻辑。它随后在完成时生成一个包含< Error >节点的XML文件。如果这个节点是空的，那么它就工作了。如果文件不存在或节点包含文本...它失败了。然后，我读取这个XML文件，并将< Error >节点的内容传递回Web Api中的客户机。

此时，从调用CMD/Progress小应用程序到尝试读取XML文件有10秒的静态延迟，以给予服务器运行.P文件和创建所述XML文件的时间。然而，这并不是很好，偶尔会向客户端返回一个错误，因为它找不到文件，然而，由于异常高的服务器负载，该文件是在响应返回后1秒创建的。或者，人们被迫等待10秒，而响应本可以在2秒内处理。

我需要想出一种“检查直到文件存在”的方法，直到超时时间过去。我做了一些研究，但找不到任何适合Web Api环境的东西。有人有什么建议吗？

下面的代码-请原谅我。我已经学到了很多，因为我一直在学习，并且对此非常陌生！

控制器

// the request date/time
DateTime requestDate = DateTime.Now;
// list of validation errors
List<string> ohValidation = new List<string>();

..。

WebExtensions.callInsertProgram(xml, "JOBLOG");
ohValidation =     XmlExtensions.ReadProgressXmlFileWithArray(job.logjob.placeref, requestDate, "joblogging");

CallInsertProgram

   public static void callInsertProgram(string xml, string program)
    {

        try
        {
            using (Process p = new Process())
            {
                p.StartInfo.FileName = @"C:\Rubixx\runProgress.exe";
                p.StartInfo.WorkingDirectory = @"C:\Rubixx";
                // stop windows from appearing on the server
                p.StartInfo.UseShellExecute = false;
                p.StartInfo.CreateNoWindow = true;
                // set the arguments for running. The program name and xml are passed in as arguments
                // wrapped in escaping "\" to stop spaces from being treated as a separator
                p.StartInfo.Arguments = "\"" + program + "," + xml + "\"";
                p.Start();
            }
        }
        catch (Exception e)
        {
            throw new OpenHousingException(e.Message.ToString());
        }

    }

ReadProgressXMLWithArray

public static List<string> ReadProgressXmlFileWithArray(string reference, DateTime requestDateTime, string folder)
    {
        // new empty list
        List<string> output 
            = new List<string>();

        // wait X seconds before doing anything 
        // to ensure the XML file has time to be created
        Delay_Start(fileDelay);

        // 
        string filename = fullFileName(jobno, folder, requestDateTime);
        string filepath = getFullFilepath(filename, folder);
        if (checkXmlFileExists(filepath))
        {
            // if so check for the existence of an error message
            output = getXmlErrorArray(filepath);
        }
        else
        {
            // if no file is found - the call to Progress hasn't executed. So tell the end user.
            throw new OpenHousingException("No OpenHousing file could be found");
        }

        return output;
    }

Delay_Start

    private static void Delay_Start(int Seconds)
    {
        DateTime StartTime;
        DateTime EndTime;

        StartTime = DateTime.Now;
        EndTime = StartTime.AddSeconds(Seconds);

        do
        { StartTime = DateTime.Now; } while (StartTime < EndTime);
    }

FullFileName (需要，因为在创建之前我不能确定XML文件名。文件格式为UniqueReference_DateTimeFileCreated.xml (xxxxxxxx_20160401-1100.xml)，因此，我必须使用通配符搜索具有唯一引用的文件夹。

    public static string fullFileName(string jobNo, string folder, DateTime createdDate)
    {
        string fileName = string.Empty;
        string folderPath = fileLocation + folder;
        DirectoryInfo dir = new DirectoryInfo(folderPath);
        FileInfo[] files = dir.GetFiles(jobNo + "*", SearchOption.TopDirectoryOnly).Where(f => f.CreationTimeUtc > createdDate || f.LastWriteTimeUtc > createdDate).ToArray() ;
        foreach (var item in files)
        {
            fileName = item.Name;
        }

        if (string.IsNullOrEmpty(fileName))
            throw new OpenHousingException("No OpenHousing file could be found");

        return fileName;
    }

GetFullFilePath (可以整合到fullFileName中)

    private static string getFullFilepath(string filename, string folder)
    {
        return fileLocation + folder + @"\" + filename;
    }

CheckXMLFileExists

    private static bool checkXmlFileExists(string filepath)
    {
        bool fileExists = false;

        if (File.Exists(filepath))
        {
            fileExists = true;
        }

        return fileExists;
    }

GetXMLErrorArray

    private static List<string> getXmlErrorArray(string filepath)
    {

        List<string> output
            = new List<string>();

        // read the text from XML file
        using (TextReader txtReader = new StreamReader(filepath))
        {
            XmlSerializer xs
                = new XmlSerializer(typeof(JobError));

            // de-serialise the xml text
            // to a strongly typed object
            JobError result = (JobError)xs.Deserialize(txtReader);

            // if the xml file contains an error - return it to the client
            if (!string.IsNullOrEmpty(result.ErrorText))
                output.Add(result.ErrorText);

            //check for SoR errors that are created under a different node
            if (result.LineError != null)
            {
                List<LineError> lineErrs = result.LineError.ToList();

                foreach (LineError le in lineErrs)
                {
                    output.Add(le.SorCode + ":" + le.Error);
                }
            }
        }

        return output;

    }