C#异步编程基础

1. 任务完成时的处理

 1 class Program
 2     {
 3         private static void Main(string[] args)
 4         {
 5             ProcessTaskAsync();
 6             Console.ReadLine();
 7         }
 8         static async Task ProcessTaskAsync()
 9         {
10             //按顺序await每个任务
11             //创建任务队列
12             Task<int> taskA = DelayAndReturnAsync(5);
13             Task<int> taskB = DelayAndReturnAsync(2);
14             Task<int> taskC = DelayAndReturnAsync(8);
15             var tasks1 = new[] { taskA, taskB, taskC };
16             Console.WriteLine("============================");
17             Console.WriteLine("============按顺序===========");
18             foreach (var task in tasks1)
19             {
20                 var result = await task;
21                 Console.WriteLine(result);
22             }
23             //输出5，2，8
24 
25             //按处理速度
26             //创建任务队列
27             Task<int> task1 = DelayAndReturnAsync(5);
28             Task<int> task2 = DelayAndReturnAsync(2);
29             Task<int> task3 = DelayAndReturnAsync(8);
30             var tasks2 = new[] { task1, task2, task3 };
31             Console.WriteLine("============================");
32             Console.WriteLine("==========按处理速度=========");
33             var processingTasks = tasks2.Select(async t =>
34               {
35                   var result = await t;
36                   Console.WriteLine(result);
37               }).ToArray();
38             //等待全部处理过程完成
39             await Task.WhenAll(processingTasks);
40             //输出2，5，8
41         }
42         static async Task<int> DelayAndReturnAsync(int val)
43         {
44             await Task.Delay(TimeSpan.FromSeconds(val));
45             return val;
46         }
47     }

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2. 等待任意一个任务完成

 1 class Program
 2     {
 3         private static void Main(string[] args)
 4         {
 5             FirstRespondingUrlAsync();
 6             Console.ReadLine();
 7         }
 8         static async Task FirstRespondingUrlAsync()
 9         {
10             var httpClient = new HttpClient();
11             string url1 = "https://www.baidu.com";
12             string url2 = "https://www.cnblogs.com/";
13             //并发地开始两个下载任务
14             Task<byte[]> task1 = httpClient.GetByteArrayAsync(url1);
15             Task<byte[]> task2 = httpClient.GetByteArrayAsync(url2);
16             //等待任意一个任务完成
17             Task<byte[]> completedTask = await Task.WhenAny(task1, task2);
18             //返回从URL得到的数据长度
19             byte[] data = await completedTask;
20             Console.WriteLine(data.Length);
21         }
22     }

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