C# async await 学习笔记1

由于我的开发工具为vs.net 2010（.net 4.0)，需先做以下两步才能进行：

1.下载并安装Async CTP (http://www.microsoft.com/en-us/download/details.aspx?id=9983)

2.添加AsyncCtpLibrary.dll的引用，我用的是win7在（C:UsersAdministratorDocumentsMicrosoft Visual Studio Async CTPSamples）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static Task<string> LongTimeTask()
        {          
            Console.WriteLine("LongTimeTask开始:" + DateTime.Now.ToString() + "  ThreadId:" + Thread.CurrentThread.ManagedThreadId);

            Task<string> task = new Task<string>(() => { Thread.Sleep(5000); return "这是任务返回值"; });
            task.Start();

            Console.WriteLine("LongTimeTask结束:" + DateTime.Now.ToString());

            return task;
        }

        static async void AsyncCall()
        {
            Console.WriteLine("AsyncCall开始：" + DateTime.Now.ToString() + "  ThreadId:" + Thread.CurrentThread.ManagedThreadId);

            string result = await LongTimeTask(); //await调用的方法需要返回Task或Task<T>，且调用await所在的方法要有async关键字
            Console.WriteLine("AsyncCall:" + result);

            Console.WriteLine("AsyncCall结束:" + DateTime.Now.ToString());
        }   

        static void Main(string[] args)
        {
            Console.WriteLine("Main开始：" + DateTime.Now.ToString() + "  ThreadId:" +Thread.CurrentThread.ManagedThreadId);
            AsyncCall();   
            Console.WriteLine("Main结束:" + DateTime.Now.ToString());      
            Console.ReadLine();
        }
    }
}

运行结果：

 不知大家注意到，里面的ThreadId是一致的。

 需要注意的是，并不是加了async，就是异步了（而是得里面有调用await方法），例如，下面其实是同步执行的

 static async void SyncCall()
        {
            Thread.Sleep(5000);
        }

        static void Main(string[] args)
        {
            Console.WriteLine("Main开始：" + DateTime.Now.ToString());
            // AsyncCall();
            SyncCall();
            Console.WriteLine("Main结束:" + DateTime.Now.ToString());

            Console.ReadLine();
        }