应用场景

     异步同时请求多个地址，获得返回的信息并输出，排除时间响应太久的以免造成不必要的时间等待。

   

1   class Program 2     { 3         static void Main(string[] args) 4         { 5             TaskTest(); 6             Console.ReadLine(); 7         } 8  9         static async void ddd()10         {11             Stopwatch sw = new Stopwatch();12             sw.Start();13             List
      
        urls = new List
       
        () { "http://www.baidu.com", "http://www.360.com" };14             string a = await DownloadAllAsync(urls);15 16             Console.WriteLine(a);17             sw.Stop();18             Console.WriteLine(sw.ElapsedMilliseconds);19             Console.ReadLine();20         }21         static HttpClient httpClient = new HttpClient();22         static async Task
        
          DownloadAllAsync(IEnumerable
         
           urls)23         {24 25             var downloads = urls.Select(url => httpClient.GetStringAsync(url));26             Task
          
           [] downloadTasks = downloads.ToArray();27 28             string[] pages = await Task.WhenAll(downloadTasks);29 30             return string.Concat(pages);31         }32 33         static void TaskTest()34         {35             var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(2000));36             Task
           
             t1 = GetString("http://www.baidu.com");37 Task
            
              t2 = GetString("http://www.360.com");38 Task
             
               t3 = GetString("http://www.github.com");39 40 Task
              
               [] arr = new Task
               
                [] { t1, t2, t3 };41 Task.WaitAll(arr,2000);42 foreach (var dd in arr)43 Console.WriteLine(dd.Result.ToString());44 }45 46 static async Task
                
                  GetString(string str)47 {48 return await httpClient.GetStringAsync(str);49 50 }