关于WebClient超时问题
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在用C#实现一个Http消息推送时，用了WebClient.UpdateString，结果发现该函数在http消息没有返回时会被阻塞。
经测试，阻塞超时是100秒。如果使用默认超时，将会大大影响推送效率，经检索资料，发现WebClient类没有超时设置。
这里查到有两种方案解决。
方案1
重写WebClient类，增加超时设置，实现起来还是比较简单
public class WebClientEx : WebClient { public int Timeout {get; set;} protected override WebRequest GetWebRequest(Uri address) { var request = base.GetWebRequest(address); request.Timeout = Timeout; return request; } } 使用 var myClient = new WebClientEx(); myClient.Timeout = 900000 // Daft timeout period myClient.UploadData(myUri, myData);
方案2
使用异步方法 WebClient.UploadStringAsync (Uri, String)
此方法的缺点是，一旦调用失败，无法直接获取调用的url，但也很容易解决，有两个办法
1）使用这个方法，第三个参数可以存放自定义数据
然后在回调函数中从 e.UserState中获取；
2）同方案1中重写WebClient类，并添加成员变量m_url，调用时自己保存相关信息，等进入回调函数时可以使用。
相关代码：
private static void UploadStringCallback2(Object sender, UploadStringCompletedEventArgs e) { //string reply = (string)e.Result; 发生异常时Result是null，正常时是返回信息 WebClientEx wc = (WebClientEx)sender; string str = wc.GetRequestURL(); string strlog = e.UserState.ToString(); strlog = e.Error.ToString(); } } public class WebClientEx : WebClient { public string m_strURL; public int Timeout { get; set; } protected override WebRequest GetWebRequest(Uri address) { var request = base.GetWebRequest(address); request.Timeout = Timeout; m_strURL = address.OriginalString; return request; } public string GetRequestURL() { return m_strURL; } }//===使用WebClientEx wc = new WebClientEx(); //WebClient wc = new WebClientEx(); //wc.Timeout = 3000; wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded");//可以post提交 wc.Encoding = Encoding.UTF8; //string[] pinfo = ConfigurationManager.AppSettings["EnableProxy"].Split('|'); //if (pinfo[0].ToLower() == "true") //{ // wc.Proxy = new WebProxy(pinfo[1], int.Parse(pinfo[2])); //} string postData = "a=12345&b=abcde"; string m_url = "http://localhost:16910/testpost.ashx"; wc.m_strURL = m_url; string result = ""; Stopwatch timer = new Stopwatch(); wc.UploadStringCompleted += new UploadStringCompletedEventHandler(UploadStringCallback2); timer.Start(); try { wc.UploadStringAsync(new Uri(m_url), "POST", postData, (object)m_url); //wc.UploadString(m_url, postData); } catch (System.Exception ex) { result = ex.Message; } timer.Stop(); result +=" use:" +(timer.ElapsedMilliseconds / 1000).ToString(); 另，在使用异步下载时，有朋友说网络中断会导致卡死，并给了解决方案，贴在这里备用
创建计时器监视响应情况，过期则取消下载
public class Calculagraph
{ 
/// <summary>
/// 时间到事件
/// </summary> public event TimeoutCaller TimeOver; /// <summary> /// 开始时间 /// </summary> private DateTime _startTime; private TimeSpan _timeout = new TimeSpan(0, 0, 10); private bool _hasStarted = false; object _userdata; /// <summary> /// 计时器构造方法 /// </summary> /// <param name="userdata">计时结束时回调的用户数据</param> public Calculagraph(object userdata) { TimeOver += new TimeoutCaller(OnTimeOver); _userdata = userdata; } /// <summary> /// 超时退出 /// </summary> /// <param name="userdata"></param> public virtual void OnTimeOver(object userdata) { Stop(); } /// <summary> /// 过期时间(秒) /// </summary> public int Timeout { get { return _timeout.Seconds; } set { if (value <= 0) return; _timeout = new TimeSpan(0, 0, value); } } /// <summary> /// 是否已经开始计时 /// </summary> public bool HasStarted { get { return _hasStarted; } } /// <summary> /// 开始计时 /// </summary> public void Start() { Reset(); _hasStarted = true; Thread th = new Thread(WaitCall); th.IsBackground = true; th.Start(); } /// <summary> /// 重置 /// </summary> public void Reset() { _startTime = DateTime.Now; } /// <summary> /// 停止计时 /// </summary> public void Stop() { _hasStarted = false; } /// <summary> /// 检查是否过期 /// </summary> /// <returns></returns> private bool checkTimeout() { return (DateTime.Now - _startTime).Seconds >= Timeout; } private void WaitCall() { try { //循环检测是否过期 while (_hasStarted && !checkTimeout()) { Thread.Sleep(1000); } if (TimeOver != null) TimeOver(_userdata); } catch (Exception) { Stop(); } }
} /// <summary> /// 过期时回调委托 /// </summary> /// <param name="userdata"></param> public delegate void TimeoutCaller( object userdata);
public class CNNWebClient : WebClient { private Calculagraph _timer; private int _timeOut = 10; /// <summary> /// 过期时间 /// </summary> public int Timeout { get { return _timeOut; } set { if (value <= 0) _timeOut = 10; _timeOut = value; } } /// <summary> /// 重写GetWebRequest,添加WebRequest对象超时时间 /// </summary> /// <param name="address"></param> /// <returns></returns> protected override WebRequest GetWebRequest(Uri address) { HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address); request.Timeout = 1000 * Timeout; request.ReadWriteTimeout = 1000 * Timeout; return request; } /// <summary> /// 带过期计时的下载 /// </summary> public void DownloadFileAsyncWithTimeout(Uri address, string fileName, object userToken) { if (_timer == null) { _timer = new Calculagraph(this); _timer.Timeout = Timeout; _timer.TimeOver += new TimeoutCaller(_timer_TimeOver); this.DownloadProgressChanged += new DownloadProgressChangedEventHandler(CNNWebClient_DownloadProgressChanged); } DownloadFileAsync(address, fileName, userToken); _timer.Start(); } /// <summary> /// WebClient下载过程事件，接收到数据时引发 /// </summary> /// <param name="sender"></param> /// <param name="e"></param> void CNNWebClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e) { _timer.Reset();//重置计时器 } /// <summary> /// 计时器过期 /// </summary> /// <param name="userdata"></param> void _timer_TimeOver(object userdata) { this.CancelAsync();//取消下载 } } 参考：
https://stackoverflow.com/questions/1237966/how-can-i-change-the-time-limit-for-webclient-uploaddata
http://www.cnblogs.com/heros/archive/2009/07/06/1517997.html
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