C# 异步编程

关于“同步”和“异步”介绍可以先看这篇文章：真的理解同步和异步了吗？

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使用Task对象来实现多线程async/async方式异步编程：

public class Program
    {
        static int i = 0;
        static void Main(string[] args)
        {
            Console.WriteLine("主线程：{0},当前时间：{1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:MM:ss"));
            TestAsycAsync();
            i++;
            Console.WriteLine("i="+i);
            Console.WriteLine("主线程结束：{0},当前时间：{1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:MM:ss"));

            Console.ReadKey();
        }

        public static async Task TestAsycAsync()
        {
            Console.WriteLine("当前线程是：{0},当前时间：{1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:MM:ss"));
            i = await GetReturnResult();
            Console.WriteLine("i=" + i);
            Console.WriteLine("当前线程是：{0},当前时间：{1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:MM:ss"));
        }

        static async Task<int> GetReturnResult()
        {
            Console.WriteLine("当前线程是：{0},当前时间：{1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:MM:ss"));

            //异步开始
            int s = await Task.Run(() =>
            {               
                Console.WriteLine("当前线程是：{0},当前时间：{1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:MM:ss"));
                Thread.Sleep(3000);  //睡眠3s
                i++;
                return i;
            });

            return s;
        }
    }

执行顺序：

蓝色标记是主线程，红色标记为异步线程，可以看到当主线执行到await之前程序都是正常运行，在遇到await时，主线程在此方法运行结束，回到原调用的地方，异步线程开始与主线程同时执行。