WebApi 请求中的取消

Question

关于使用 CancellationTokens 取消 WebApi 请求的资源有多种，例如（这个概念似乎适用于所有最新版本）：

现在我还了解到，通常对于 HTTP 连接，您不会在每次发送新请求时打开和关闭 TCP 连接，但通常会让 TCP 连接保持打开状态，至少我是这样理解这篇文章的MDN：A typical HTTP session.

所以我的问题是：

如果我从 C# 发出 HTTP 请求，是否每次都会建立和关闭底层 TCP 连接，以便该机制基本上是关闭 TCP 连接并且服务器可以请求令牌中的取消？

所以这最终是否依赖于我总是为每个请求打开一个新的 TCP 连接这一事实？或者在 TCP 连接不会关闭的情况下是否还有其他东西（也）可以工作？

Answer 1

这是 Github.

中 HttpWebrequest.Abort() 方法的源代码

     private void Abort(Exception exception, int abortState)
    {
        GlobalLog.ThreadContract(ThreadKinds.Unknown, "HttpWebRequest#" + ValidationHelper.HashString(this) + "::Abort()");
        if (Logging.On) Logging.Enter(Logging.Web, this, "Abort", (exception == null? "" :  exception.Message));

        if(Interlocked.CompareExchange(ref m_Aborted, abortState, 0) == 0) // public abort will never drain streams
        {
            GlobalLog.Print("HttpWebRequest#" + ValidationHelper.HashString(this) + "::Abort() - " + exception);

            NetworkingPerfCounters.Instance.Increment(NetworkingPerfCounterName.HttpWebRequestAborted);

            m_OnceFailed = true;
            CancelTimer();

            WebException webException = exception as WebException;
            if (exception == null)
            {
                webException = new WebException(NetRes.GetWebStatusString("net_requestaborted", WebExceptionStatus.RequestCanceled), WebExceptionStatus.RequestCanceled);
            }
            else if (webException == null)
            {
                webException = new WebException(NetRes.GetWebStatusString("net_requestaborted", WebExceptionStatus.RequestCanceled), exception, WebExceptionStatus.RequestCanceled, _HttpResponse);
            }

            try
            {

                    // Want to make sure that other threads see that we're aborted before they set an abort delegate, or that we see
                    // the delegate if they might have missed that we're aborted.
                    Thread.MemoryBarrier();
                    HttpAbortDelegate abortDelegate = _AbortDelegate;

                    if (abortDelegate == null || abortDelegate(this, webException))
                    {
                        // We don't have a connection associated with this request

                        SetResponse(webException);
                    }
                    else
                    {
                        // In case we don't call SetResponse(), make sure to complete the lazy async result
                        // objects. abortDelegate() may not end up in a code path that would complete these
                        // objects.
                        LazyAsyncResult writeAResult = null;
                        LazyAsyncResult readAResult = null;

                        if (!Async)
                        {
                            lock (this)
                            {
                                writeAResult = _WriteAResult;
                                readAResult = _ReadAResult;
                            }
                        }

                        if (writeAResult != null)
                            writeAResult.InvokeCallback(webException);

                        if (readAResult != null)
                            readAResult.InvokeCallback(webException);
                    }

                    if (!Async)
                    {
                        LazyAsyncResult chkConnectionAsyncResult = ConnectionAsyncResult;
                        LazyAsyncResult chkReaderAsyncResult = ConnectionReaderAsyncResult;

                        if (chkConnectionAsyncResult != null)
                            chkConnectionAsyncResult.InvokeCallback(webException);
                        if (chkReaderAsyncResult != null)
                            chkReaderAsyncResult.InvokeCallback(webException);
                    }

                    if (this.IsWebSocketRequest && this.ServicePoint != null)
                    {
                        this.ServicePoint.CloseConnectionGroup(this.ConnectionGroupName);
                    }

            }
            catch (InternalException)
            {
            }
        }

        if(Logging.On)Logging.Exit(Logging.Web, this, "Abort", "");
    }

这清楚地表明 TCP 连接正在关闭。服务器以自己的方式响应关闭的 TCP 端口。 link : https://serverfault.com/questions/147886/what-happens-when-a-http-request-is-terminated-prematurely

Answer 2

在 HTTP 请求-响应交换之后，您无需担心连接是否关闭，因为它对取消机制没有影响。确实有影响的是，在 HTTP 请求-响应交换期间关闭连接，因为这会触发取消服务器端的请求处理，以防它处理取消令牌。所以换句话说，如果连接在发送响应之前关闭，无论连接是什么类型（保持活动或每次交换），这都是服务器启动取消过程的原因。

WebApi 请求中的取消

Cancellation in WebApi requests

c#

asp.net-web-api

cancellation-token