如何根据最佳实践在C#4中创建异步方法? [英] How to create an async method in C# 4 according to the best practices?

问题描述

请考虑以下代码段:

public static Task<string> FetchAsync()
{
    string url = "http://www.example.com", message = "Hello World!";

    var request = (HttpWebRequest)WebRequest.Create(url);
    request.Method = WebRequestMethods.Http.Post;

    return Task.Factory.FromAsync<Stream>(request.BeginGetRequestStream, request.EndGetRequestStream, null)
        .ContinueWith(t =>
        {
            var stream = t.Result;
            var data = Encoding.ASCII.GetBytes(message);
            Task.Factory.FromAsync(stream.BeginWrite, stream.EndWrite, data, 0, data.Length, null, TaskCreationOptions.AttachedToParent)
                .ContinueWith(t2 => { stream.Close(); });
        })
        .ContinueWith<string>(t =>
        {
            var t1 =
                Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, null)
                .ContinueWith<string>(t2 =>
                {
                    var response = (HttpWebResponse)t2.Result;
                    var stream = response.GetResponseStream();
                    var buffer = new byte[response.ContentLength > 0 ? response.ContentLength : 0x100000];
                    var t3 = Task<int>.Factory.FromAsync(stream.BeginRead, stream.EndRead, buffer, 0, buffer.Length, null, TaskCreationOptions.AttachedToParent)
                        .ContinueWith<string>(t4 =>
                        {
                            stream.Close();
                            response.Close();
                            if (t4.Result < buffer.Length)
                            {
                                Array.Resize(ref buffer, t4.Result);
                            }
                            return Encoding.ASCII.GetString(buffer);
                        });
                    t3.Wait();
                    return t3.Result;
                });
            t1.Wait();
            return t1.Result;
        });
}

它应该返回Task<string>，发送带有一些数据的HTTP POST请求，以字符串形式从Web服务器返回结果，并应尽可能高效.

It should return Task<string>, send HTTP POST request with some data, return a result from webserver in a form of string and be as much efficient as possible.

• 在上面的示例中，您发现与异步流有关的任何问题吗?
• 在此示例中，可以将.Wait()包含在.ContinueWith()中
• 在这种和平的代码形式下(您暂时保留异常处理)，您还看到其他任何问题吗?

推荐答案

如果与异步相关的C#4.0代码庞大而丑陋-可能会正确实施该代码.如果它又好又短，那么很可能不是;)

If async related C# 4.0 code is huge and ugly - there is a chance that it's implemented properly. If it's nice and short, then most likely it's not ;)

..尽管如此，通过在WebRequest上创建扩展方法，Stream类并清除main方法，您可能会使其看起来更具吸引力.

..though, you may get it look more attractive by creating extension methods on WebRequest, Stream classes and cleanup the main method.

PS :我希望C#5.0带有新的async关键字和库即将发布.

P.S.: I hope C# 5.0 with it's new async keyword and library will be released soon.

参考: http://msdn.microsoft .com/en-us/vstudio/async.aspx

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