异步是否会在此示例中带来任何好处？

Question

我正在尝试学习C#中的机制async和await机制.

在最简单的例子我很清楚.

这条线

Task<string> getStringTask = client.GetStringAsync("http://msdn.microsoft.com");

触发异步Web调用.控件返回AccessTheWebAsync().它是免费的DoIndependentWork().这样做了以后它等待任务的完成getStringTask,当这个结果可在函数执行的下一行 return urlContents.Length; 所以,据我了解的目的async呼叫,让呼叫者执行其他操作时,标签的操作与async在进展.

但是,在这个函数中,我对这个例子有点困惑.

    private async Task<byte[]> GetURLContentsAsync(string url)
    {
        // The downloaded resource ends up in the variable named content. 
        var content = new MemoryStream();

        // Initialize an HttpWebRequest for the current URL. 
        var webReq = (HttpWebRequest)WebRequest.Create(url);

        // Send the request to the Internet resource and wait for 
        // the response.                 
        using (WebResponse response = await webReq.GetResponseAsync())

        // The previous statement abbreviates the following two statements. 

        //Task<WebResponse> responseTask = webReq.GetResponseAsync(); 
        //using (WebResponse response = await responseTask)
        {
            // Get the data stream that is associated with the specified url. 
            using (Stream responseStream = response.GetResponseStream())
            {
                // Read the bytes in responseStream and copy them to content. 
                await responseStream.CopyToAsync(content);

                // The previous statement abbreviates the following two statements. 

                // CopyToAsync returns a Task, not a Task<T>. 
                //Task copyTask = responseStream.CopyToAsync(content); 

                // When copyTask is completed, content contains a copy of 
                // responseStream. 
                //await copyTask;
            }
        }
        // Return the result as a byte array. 
        return content.ToArray();
    }

在方法内部GetURLContentsAsync(),有两个异步调用.但是,API会同时await调用两者.调用者在操作的触发器和数据的接收之间没有做任何事情async.所以,据我所知,这个async/await机制在这里没有任何好处.我错过了一些明显的东西吗？

Answer 1

您的代码不需要在await'd异步调用之间明确地执行任何操作以获得收益.这意味着线程没有等待每个调用完成,它可以做其他工作.

如果这是一个Web应用程序,则可能导致处理更多请求.如果它是Windows应用程序,则意味着UI线程未被阻止,并且用户具有更好的体验.