c# - 异步 Web 请求超时 => 使 IIS 崩溃

Question

我有一个网络应用程序，它从外部服务获取数据。请求本身就像下面的代码一样——据我所知非常简单。创建一个请求，异步触发它并让回调处理响应。在我的开发环境中运行良好。

public static void MakeRequest(Uri uri, Action<Stream> responseCallback)
        {
            WebRequest request = WebRequest.Create(uri);
            request.Proxy = null;
            request.Timeout = 8000;
            try
            {
                Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, null)
                    .ContinueWith(task =>
                                      {
                                          WebResponse response = task.Result;
                                          Stream responseStream = response.GetResponseStream();
                                          responseCallback(response.GetResponseStream());
                                          responseStream.Close();
                                          response.Close();
                                      });
            } catch (Exception ex)
            {
                _log.Error("MakeRequest to " + uri + " went wrong.", ex);
            }
        }

但是，由于我以外的原因，外部测试环境和生产环境可能无法访问目标 URL。好吧，我想——请求超时不会真正伤害到任何人。然而，似乎每次这个请求超时时，ASP.NET 崩溃并且 IIS 被重新启动。事件日志向我显示了这个堆栈跟踪:

StackTrace:    at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.get_Result()
   at MyApp.AsyncWebClient.<>c__DisplayClass2.<MakeRequest>b__0(Task`1 task)
   at System.Threading.Tasks.Task`1.<>c__DisplayClass17.<ContinueWith>b__16(Object obj)
   at System.Threading.Tasks.Task.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()

InnerException: System.Net.WebException

Message: Unable to connect to the remote server

StackTrace:    at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endMethod, TaskCompletionSource`1 tcs)

InnerException: System.Net.Sockets.SocketException

Message: 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

StackTrace:    at System.Net.Sockets.Socket.EndConnect(IAsyncResult asyncResult)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception)

..所以在我看来，这一切都归结为 SocketException。紧接着(在同一秒内)记录了另一个事件(我猜是相关的):

Exception Info: System.AggregateException
Stack:
   at System.Threading.Tasks.TaskExceptionHolder.Finalize()

这有点超出我的理解范围，因为我不是异步代码和线程的专家，但是 Web 请求的超时导致 IIS 崩溃似乎很奇怪。我重新实现了 MakeRequest 以同步执行请求，效果很好。在这些环境中，请求仍然会超时，但不会造成任何损坏，并且应用程序会在之后继续愉快地运行。

所以我已经解决了我的问题，但为什么会这样呢？谁能启发我？ :-)

Answer 1

您的延续需要处理 .Result 可能反射(reflect)异常的事实。否则你有一个未处理的异常。未处理的异常终止进程。

.ContinueWith(task =>
{
    try {
        WebResponse response = task.Result;
        Stream responseStream = response.GetResponseStream();
        responseCallback(responseStream);
        responseStream.Close();
        response.Close();
    } catch(Exception ex) {
        // TODO: log ex, etc
    }
});

您的旧异常处理程序仅涵盖任务的创建 - 不包括回调。