如何使用 async 和 await 发出大量并发 Web 请求？

Question

我阅读了 Microsoft 的操作方法，网址为 How to: Make Multiple Web Requests in Parallel by Using async and await (C#) 并发现：

private async Task CreateMultipleTasksAsync()  
{  
    // Declare an HttpClient object, and increase the buffer size. The  
    // default buffer size is 65,536.  
    HttpClient client =  
        new HttpClient() { MaxResponseContentBufferSize = 1000000 };  

    // Create and start the tasks. As each task finishes, DisplayResults   
    // displays its length.  
    Task<int> download1 =   
        ProcessURLAsync("http://msdn.microsoft.com", client);  
    Task<int> download2 =   
        ProcessURLAsync("http://msdn.microsoft.com/library/hh156528(VS.110).aspx", client);  
    Task<int> download3 =   
        ProcessURLAsync("http://msdn.microsoft.com/library/67w7t67f.aspx", client);  

    // Await each task.  
    int length1 = await download1;  
    int length2 = await download2;  
    int length3 = await download3;  

    int total = length1 + length2 + length3;  

    // Display the total count for the downloaded websites.  
    resultsTextBox.Text +=  
        string.Format("\r\n\r\nTotal bytes returned:  {0}\r\n", total);  
}

我理解这段代码，但我的问题是：我如何修改它以将其缩放到喜欢的程度，比方说一百或一千？

Answer 1

您可以在循环中调用异步调用。每次调用可能 return 一个任务，您必须等待所有任务完成

var requestInfoCollection = new RequestInfo[]
{
     new RequestInfo("http://url1","GET"),
     new RequestInfo("http://url2","GET"),
     new RequestInfo("http://url2","POST")
};
List<Task> tasks = new List<Task>();
foreach(var requestInfo in requestInfoCollection)
{
   tasks.Add(ProcessURLAsync(requestInfo))
}
Task.WaitAll(tasks);

以上将调用多个请求并等待结果，但是 async\await 有助于释放线程以供应用程序在执行外部调用（http、db 等...）时使用。但扩展取决于您的硬件和应用程序架构。

Answer 2

由于我的帐户限制，我无法发表评论，但回复@CreativeManix 的回答，

List<Task> tasks = new List<Task>();

Task.WaitAll(tasks) 将不接受任务列表。它的覆盖之一接受任务数组。

Task.WaitAll(tasks.ToArray())

如何使用 async 和 await 发出大量并发 Web 请求？

How to make a lot of concurrent web requests using async and await?

.net

c#

asynchronous

concurrent-processing