C# 异步编程

C# async/await特性可以创建b并使用异步方法

await表达式

await表达式指定了一个异步执行的任务

取消一个异步操作

CancellationTokenSource和CancellationToken来实现取消操作。

调用CancellationTokenSource的Cancel时，它本身不会执行取消操作。而是会将CancellationToken的IsCancellationRequest属性设置为true。

 class Program
    {
        static void Main(string[] args)
        {
         
            CancellationTokenSource cts = new CancellationTokenSource();
            CancellationToken token = cts.Token;

            MyClass my = new MyClass();
            Task t = my.RunAsync(token);

            Thread.Sleep(3000);
    //        cts.Cancel();
            //Console.ReadKey();
            t.Wait();

            Console.WriteLine("Was Cancelled:{0}", token.IsCancellationRequested);
            Console.ReadKey();
        }
    }

  class MyClass
    {
       
       

        internal async Task RunAsync(CancellationToken token)
        {
            if (token.IsCancellationRequested)
            {
                return;
            }
            await Task.Run(() => CycleMethod(token), token);
        }

        void CycleMethod(CancellationToken ct)
        {
            Console.WriteLine("Starting CycleMethod");
            const int Max = 5;
            for (int i = 0; i < Max; i++)
            {
                if (ct.IsCancellationRequested)
                {
                    return;
                }
     //           Thread.Sleep(1000);
                Console.WriteLine("   {0} of {1} iterations completed", i + 1, Max);
            }
        }
    }

在调用方法中同步等待任务