异步任务超时

我有这段代码来发出异步 HTTP 请求：

    public static void MakeRequest(Uri uri, Action<RequestCallbackState> responseCallback)
    {
        WebRequest request = WebRequest.Create(uri);
        request.Proxy = null;

        Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, null).ContinueWith(task =>
            {
                WebResponse response = task.Result;
                Stream responseStream = response.GetResponseStream();
                responseCallback(new RequestCallbackState(response.GetResponseStream()));
                responseStream.Close();
                response.Close();
            });
    }

它有效，但我需要设置请求超时。我尝试使用 request.Timeout 但似乎没有做任何事情。有没有办法在此代码中设置任务超时？

编辑以添加新的超时回调。 新代码：

    public static void MakeRequest(Uri uri, Action<RequestCallbackState> responseCallback)
    {
        WebRequest request = WebRequest.Create(uri);
        request.Proxy = null;

        IAsyncResult t = Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, null).ContinueWith(task =>
            {
                WebResponse response = task.Result;
                Stream responseStream = response.GetResponseStream();
                responseCallback(new RequestCallbackState(response.GetResponseStream()));
                responseStream.Close();
                response.Close();
            });
        ThreadPool.RegisterWaitForSingleObject(t.AsyncWaitHandle, new WaitOrTimerCallback(TimeoutCallback), request, 1000, true);
    }

    private static void TimeoutCallback(object state, bool timedOut)
    {
        if (timedOut)
        {
            Console.WriteLine("Timeout");
            WebRequest request = (WebRequest)state;
            if (state != null)
            {
                request.Abort();
            }
        }
    }

测试：

HttpSocket.MakeRequest(new Uri("http://www.google.comhklhlñ"), callbackState =>
    {
        if (callbackState.Exception != null)
            throw callbackState.Exception;
        Console.WriteLine(GetResponseText(callbackState.ResponseStream));
    });
Thread.Sleep(10000);

来自超时文档:

Timeout 属性对使用 BeginGetResponse 或 BeginGetRequestStream 方法发出的异步请求没有影响。

这是因为框架强制您自己处理超时。您应该能够使用示例代码在这里，除了通过Task从返回FromAsync致电ThreadPool.RegisterWaitForSingleObject method.

Edit:

您需要将注册放在原始任务上，而不是延续上：

public static void MakeRequest(Uri uri, Action<Stream> responseCallback)
{
    WebRequest request = WebRequest.Create(uri);
    request.Proxy = null;
    const int TimeoutPeriod = 1000;

    Task<WebResponse> t = Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, null);
    ThreadPool.RegisterWaitForSingleObject((t as IAsyncResult).AsyncWaitHandle, TimeoutCallback, request, TimeoutPeriod, true);
    t.ContinueWith(task =>
    {
        WebResponse response = task.Result;
        Stream responseStream = response.GetResponseStream();
        responseCallback(response.GetResponseStream());
        responseStream.Close();
        response.Close();
    });
}

这对我有用（如果我将超时持续时间设置得很短，并点击此按钮，我总是会适当超时）。