取消异步httpwebrequests [英] Canceling async httpwebrequests

问题描述

我在做一个应用程序，这将使一些HttpWebRequest的对象和下载通过 HTT prequest.BeginGetResponse 方法我的HTML。我回来了的IAsyncResult 并存储在本地，这样我可以随时取消请求，但我不知道如果我正确地这样做。

I am making an app that will make several HttpWebRequest objects and downloading my html via the httpRequest.BeginGetResponse method. I get back the IAsyncResult and store it locally so that I can cancel the request at any time, but I'm not sure if I'm doing that correctly.

下面是我在做什么，以取消异步Web请求：

Here is what I'm doing to cancel the async web request:

var res = (RequestState)asyncResult.AsyncState;
res.Request.Abort();

在哪里请求的类型为的HttpWebRequest 。

什么我注意到的是，即使是在我称之为code的这些线，我仍然有所有的异步线程在我的应用程序打开的。如果我设置叫 HTT prequest.BeginGetResponse（GetResponseCallback，州）（如方法 GetResponseCallback ）的方法中的调试器中断几秒钟后，引起引发WebException时方法跑到被抛出。

What I'm noticing is that even after I call these lines of code, I still have all of the Async threads open in my application. And if I set a break point in the delegate called in httpRequest.BeginGetResponse(GetResponseCallback, state) (e.g. the method GetResponseCallback) The debugger breaks inside the method after a few seconds, causing a WebException to be thrown when that method is ran.

只是为了保持完整性，我GetResponseCallback看起来是这样的：

Just for completeness, my GetResponseCallback looks like this:

using (var httpWebResponse = (HttpWebResponse)request.EndGetResponse(result))
using (Stream dataStream = httpWebResponse.GetResponseStream())
using (var reader = new StreamReader(dataStream))
{
    string ret = reader.ReadToEnd();
    state.OnComplete(ret, new EventArgs());
}

和我上使用（流数据流= httpWebResponse.GetResponseStream（））行引发WebException。内部异常类似于服务器主动拒绝了连接像什么的。

and I get the WebException on the using (Stream dataStream = httpWebResponse.GetResponseStream()) line. The inner exception says something like "the server actively refused the connection" or something like that.

任何帮助将是极好的！

推荐答案

从的文档HttpWebRequest.Abort（）：

Abort方法取消对资源的请求。请求被取消后，调用GetResponse的，BeginGetResponse，EndGetResponse，GetRequestStream，BeginGetRequestStream或EndGetRequestStream方法使设置为RequestCanceled Status属性引发WebException。

The Abort method cancels a request to a resource. After a request is canceled, calling the GetResponse, BeginGetResponse, EndGetResponse, GetRequestStream, BeginGetRequestStream, or EndGetRequestStream method causes a WebException with the Status property set to RequestCanceled.

所以，你所描述的行为是设计使然。我认为你必须捕捉异常，否则找决定是否中止打电话之前调用的一些方法的GetResponse，BeginGetResponse，EndGetResponse，GetRequestStream，BeginGetRequestStream或EndGetRequestStream。

So the behavior you describe is by design. I think you'll have to catch the exception, or else find some way of determining whether Abort was called before calling GetResponse, BeginGetResponse, EndGetResponse, GetRequestStream, BeginGetRequestStream, or EndGetRequestStream.

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