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【已解决】C#中HttpWebRequest的GetRequestStream执行的效率太低,甚至偶尔死掉

C# crifan 3310浏览 0评论

【问题】

C#中,提交对应的POST类型http请求之前,会执行:

Stream postDataStream = req.GetRequestStream();

然后填充对应的post数据,再提交http的请求。

但是调试的时候,发现每次执行GetRequestStream都很慢。

慢也就算了,结果最近发现,某次,执行req.GetRequestStream();死掉。

【解决过程】

1.网上找了找,根据 GetRequestStream的效率为什么这么低? 的解释,说是.NET每次会自动搜索代理,所以很慢,此处没有设置代理的话,应该直接复制为空:

req.Proxy = null;

然后再去执行GetRequestStream,这样就不会慢了。

然后去试了试,好像是这个效果。

2.结果第二天同样的代码,去调试,结果GetRequestStream的地方,还是死掉了。

原因暂未知。

3.后来的情况是,同样的代码,再次运行,就不死了,虽然也还是有时候效率低,反应慢,但是不会死了。具体根本原因,感觉还是没有找到。

4. 后来的多次调试,发现对于:

req.Proxy = null;

好像也没啥效果。

只是碰巧找到了,关于设置proxy为null的原始的官方的解释:

”C# 3.0 in a Nutshell, Third Edition: A Desktop Quick Reference“的Chapter 14. Networking

Warning

If you don’t have a proxy, you must set the Proxy property to null on all WebClient and WebRequest objects. Otherwise, the Framework may attempt to "auto-detect" your proxy settings, adding up to 30 seconds to your request. If you’re wondering why your web requests execute slowly, this is probably it!

但是此处,对于我所遇到的,执行GetRequestStream会死掉的问题,还是没有啥帮助。

5.多次调试得到的结果是,如果是对于:

Stream postDataStream = req.GetRequestStream();

是单步调试的话,好像很少会死掉.

而如果直接运行,没有打断点,那么经常容易死掉.

6.参考:GetRequestStream throws Timeout exception randomly,去试了:

using (Stream postDataStream = req.GetRequestStream())
{
    postDataStream.Write(postBytes, 0, postBytes.Length);
    postDataStream.Close();
}

还是会死掉。

7.网上看到:HttpWebRequest.GetRequestStream() hangs,看起来此问题,好像已经是官方承认的一个bug。

不过即使真的是bug,其解释说是在.NET 4.0 beta2才解决掉,而我此处无法用.NET 4.0,只能用.NET 2.0/3.0/3.5,所以,如果真是bug的话,那就真的悲剧了。。。

还是先去看看,有没有其他解决办法再说吧。

8.试了如下代码:

try
{
    Stream postDataStream = req.GetRequestStream();

    postDataStream.Write(postBytes, 0, postBytes.Length);
    postDataStream.Close();
}
catch (WebException ex)
{
    MessageBox.Show(ex.Message);
}

单步调试了:

Stream postDataStream = req.GetRequestStream();

发现经过很长的时间之后,捕获到了异常WebException ex,出现了“Unable to connect to the remote server”错误,其详细信息如下:

ex	{"Unable to connect to the remote server"}	System.Net.WebException
base	{"Unable to connect to the remote server"}	System.InvalidOperationException {System.Net.WebException}
base	{"Unable to connect to the remote server"}	System.SystemException {System.Net.WebException}
base	{"Unable to connect to the remote server"}	System.Exception {System.Net.WebException}
_className	null	string
_data	null	System.Collections.IDictionary
_dynamicMethods	null	object
_exceptionMethod	null	System.Reflection.MethodBase
_exceptionMethodString	null	string
_helpURL	null	string
_HResult	-2146233079	int
_innerException	{"A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 65.55.254.42:443"}	System.Exception {System.Net.Sockets.SocketException}
_message	"Unable to connect to the remote server"	string
_remoteStackIndex	0	int
_remoteStackTraceString	null	string
_source	null	string
_stackTrace	{sbyte[96]}	object {sbyte[]}
_stackTraceString	null	string
_xcode	-532459699	int
_xptrs	0	System.IntPtr
Data	{System.Collections.ListDictionaryInternal}	System.Collections.IDictionary {System.Collections.ListDictionaryInternal}
HelpLink	null	string
HResult	-2146233079	int
InnerException	{"A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 65.55.254.42:443"}	System.Exception {System.Net.Sockets.SocketException}
IsTransient	false	bool
Message	"Unable to connect to the remote server"	string
Source	"System"	string
StackTrace	"   at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)\r\n   at System.Net.HttpWebRequest.GetRequestStream()\r\n   at InsertSkydriveFiles.skydrive.beforeUploadFile()"	string
TargetSite	{System.IO.Stream GetRequestStream(System.Net.TransportContext ByRef)}	System.Reflection.MethodBase {System.Reflection.RuntimeMethodInfo}
Static members		
InternalStatus	ServicePointFatal	System.Net.WebExceptionInternalStatus
m_InternalStatus	ServicePointFatal	System.Net.WebExceptionInternalStatus
m_Response	null	System.Net.WebResponse
m_Status	ConnectFailure	System.Net.WebExceptionStatus
Response	null	System.Net.WebResponse
Status	ConnectFailure	System.Net.WebExceptionStatus

此处觉得很不能理解的事情是,我只是调用GetRequestStream,获得request的stream,又不是来自服务器端的response,为何也要去链接remote server,而不是本地调用一个库函数,获得对应的stream???

 

【后记 2012-03-01】

后来发现,好像此问题,和GetResponse偶尔死掉,是同一个原因,然后也解决了这个问题,具体过程和办法,请参考:

【已解决】HttpWebRequest的GetResponse或GetRequestStream偶尔超时 + 总结各种超时死掉的可能和相应的解决办法

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