.net - 在 .NET 中同步异步响应以将结果记录到文件中

Question

假设我在另一个方法中有以下代码：

Parallel.For(0, pageCount, 
             page =>
             {
                 var request = (HttpWebRequest)WebRequest.Create(
                                string.Format(url, 
                                    selectedRegion["id"].InnerText, page));
                 request.BeginGetResponse(
                     new AsyncCallback(FinishRequestRegion), request);
              });

这是预期响应的回调：

void FinishRequestRegion(IAsyncResult res)
        {
            try
            {
                var response = (res.AsyncState as HttpWebRequest).EndGetResponse(res) as HttpWebResponse;
                var docCitizens = new XmlDataDocument();
                var readerCitizens = new XmlTextReader(response.GetResponseStream());

                readerCitizens.MoveToContent();
                docCitizens.Load(readerCitizens);
                readerCitizens.Close();

                if (docCitizens["error"]!=null)
                    return;

                var selectedRegion = docCitizens["region"];
                var regionCitizens = selectedRegion["citizens"];

                var result = (regionCitizens.Cast<XmlNode>().Select(citizen => citizen["id"].InnerText)).ToList();

                File.AppendAllLines("list.txt",  result);

            }
            catch (Exception ex)
            {
                return;
            }

        }

当 2 个响应尝试同时写入文件时出现错误（经典消息“另一个进程正在访问文件”）。如何使并发进程等待文件被解锁，以便它可以在那里记录所需的信息？

Answer 1

你需要锁定一些东西：

object fileLock = new object();

void FinishRequestRegion(IAsyncResult res)
        {
            try
            {
                ...
                lock(fileLock)
                   File.AppendAllLines("list.txt",  result);

            }
            catch (Exception ex)
            {
                return;
            }

        }