c# - .NET 4.0 中任务中的 PostAsync() 导致 WebException

Question

以下方法的目标是异步设置并触发从桌面应用程序到 Web Controller 的 http post。我认为我们如何设置下面的任务一定有问题，我相信 .NET 4.5 中有更好的实践，例如 async/await 和 Task.Run 可以解决这个问题，但升级目前不是选项。有没有更好的方法在 .NET 4.0 中处理/编写它，以防止出现下面描述的问题？

    public void PostWithoutResponse(object objectToPost, string url) {
        Task.Factory.StartNew(() =>
        {
            using (var handler = new HttpClientHandler()) {
                handler.PreAuthenticate = true;
                handler.Credentials = _credentialPool.GetNetworkCredentials(new Uri(url));
                using (var client = new HttpClient(handler)) {
                    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                    using (var stringContent = new StringContent(JsonConvert.SerializeObject(objectToPost), Encoding.UTF8, "application/json")) {
                        // We weren't able to get this post to work without waiting for result
                        var result = client.PostAsync(url, stringContent).Result;
                    }
                }
            }
        });
    }

该方法有时只能工作 2-3 次，有时是几次，有时甚至对数百个帖子(几批处理)都有效，然后才会失败。程序继续运行，但数据库中没有反射(reflect)更多的帖子，最终抛出异常。 (可能是由于超时。)

我们能够观察到这是抛出的异常:

System.AggregateException was unhandled
Message: An unhandled exception of type 'System.AggregateException' occurred in mscorlib.dll
Additional information: One or more errors occurred.

有一个内部异常(exception):

_innerException {"The request was canceled"}    System.Exception {System.Net.WebException}

有趣的是，虽然数据库更新在 2-3 之后停止，但程序(自动批处理工作流)继续运行并且在达到此方法以获取新批处理之前似乎不会抛出异常。可能相关？

    public string GetPostResult(object objectToPost, string url) {
        string jsonResult = null;
        using (var handler = new HttpClientHandler()) {
            handler.PreAuthenticate = true;
            handler.Credentials = _credentialPool.GetNetworkCredentials(new Uri(url));
            using (var client = new HttpClient(handler)) {
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                var serializedContent = JsonConvert.SerializeObject(objectToPost);
                using (var stringContent = new StringContent(serializedContent, Encoding.UTF8, "application/json")) {
                    var taskResult = client.PostAsync(url, stringContent).Result;
                    jsonResult = taskResult.Content.ReadAsStringAsync().Result;
                }
            }
        }
        return jsonResult;
    }

我还应该提到，我们已经尝试将 try/catch 放在几个安排中，但似乎无法在任何地方捕获该异常，直到它冒出并中断运行时。

(最初似乎上面的代码在我们的开发计算机上运行，​​在生产机器上失败，但事实证明这是偶然的运气加上我们的误解。)

Answer 1

这段代码好像已经解决了.....

    public void PostWithoutResponse(object objectToPost, string url) {
        var uri = new Uri(url);
        var httpPost = (HttpWebRequest)WebRequest.Create(uri);
        httpPost.KeepAlive = false;
        httpPost.Method = "POST";
        httpPost.Credentials = _credentialPool.GetNetworkCredentials(uri);
        httpPost.ContentType = "application/json";
        using (var streamWriter = new StreamWriter(httpPost.GetRequestStream())) {
            var json = JsonConvert.SerializeObject(objectToPost);
            streamWriter.Write(json);
            streamWriter.Flush();
            streamWriter.Close();
        }
        Task.Factory.StartNew(() => httpPost.GetResponse());
    }