C#异步编程基础

1. 任务完成时的处理

class Program
    {
        private static void Main(string[] args)
        {
            ProcessTaskAsync();
            Console.ReadLine();
        }
        static async Task ProcessTaskAsync()
        {
            //按顺序await每个任务
            //创建任务队列
            Task<int> taskA = DelayAndReturnAsync(5);
            Task<int> taskB = DelayAndReturnAsync(2);
            Task<int> taskC = DelayAndReturnAsync(8);
            var tasks1 = new[] { taskA, taskB, taskC };
            Console.WriteLine("============================");
            Console.WriteLine("============按顺序===========");
            foreach (var task in tasks1)
            {
                var result = await task;
                Console.WriteLine(result);
            }
            //输出5，2，8

            //按处理速度
            //创建任务队列
            Task<int> task1 = DelayAndReturnAsync(5);
            Task<int> task2 = DelayAndReturnAsync(2);
            Task<int> task3 = DelayAndReturnAsync(8);
            var tasks2 = new[] { task1, task2, task3 };
            Console.WriteLine("============================");
            Console.WriteLine("==========按处理速度=========");
            var processingTasks = tasks2.Select(async t =>
              {
                  var result = await t;
                  Console.WriteLine(result);
              }).ToArray();
            //等待全部处理过程完成
            await Task.WhenAll(processingTasks);
            //输出2，5，8
        }
        static async Task<int> DelayAndReturnAsync(int val)
        {
            await Task.Delay(TimeSpan.FromSeconds(val));
            return val;
        }
    }

2. 等待任意一个任务完成

class Program
    {
        private static void Main(string[] args)
        {
            FirstRespondingUrlAsync();
            Console.ReadLine();
        }
        static async Task FirstRespondingUrlAsync()
        {
            var httpClient = new HttpClient();
            string url1 = "https://www.baidu.com";
            string url2 = "https://www.cnblogs.com/";
            //并发地开始两个下载任务
            Task<byte[]> task1 = httpClient.GetByteArrayAsync(url1);
            Task<byte[]> task2 = httpClient.GetByteArrayAsync(url2);
            //等待任意一个任务完成
            Task<byte[]> completedTask = await Task.WhenAny(task1, task2);
            //返回从URL得到的数据长度
            byte[] data = await completedTask;
            Console.WriteLine(data.Length);
        }
    }