C# async await 學習筆記1

由于我的開發工具為vs.net 2010（.net 4.0)，需先做以下兩步才能進行：

1.下載并安裝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:/Users/Administrator/Documents/Microsoft Visual Studio Async CTP/Samples）

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開始:" + DateTime.Now.ToString() + "  ThreadId:" + Thread.CurrentThread.ManagedThreadId);            Task<string> task = new Task<string>(() => { Thread.Sleep(5000); return "這是任務返回值"; });            task.Start();            Console.WriteLine("LongTimeTask結束:" + DateTime.Now.ToString());            return task;        }        static async void AsyncCall()        {            Console.WriteLine("AsyncCall開始：" + DateTime.Now.ToString() + "  ThreadId:" + Thread.CurrentThread.ManagedThreadId);            string result = await LongTimeTask(); //await調用的方法需要返回Task或Task<T>，且調用await所在的方法要有async關鍵字            Console.WriteLine("AsyncCall:" + result);            Console.WriteLine("AsyncCall結束:" + DateTime.Now.ToString());        }           static void Main(string[] args)        {            Console.WriteLine("Main開始：" + DateTime.Now.ToString() + "  ThreadId:" +Thread.CurrentThread.ManagedThreadId);            AsyncCall();               Console.WriteLine("Main結束:" + DateTime.Now.ToString());                  Console.ReadLine();        }    }}

運行結果：

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，就是異步了（而是得里面有調用await方法），例如，下面其實是同步執行的

 static async void SyncCall()        {            Thread.Sleep(5000);        }        static void Main(string[] args)        {            Console.WriteLine("Main開始：" + DateTime.Now.ToString());            // AsyncCall();            SyncCall();            Console.WriteLine("Main結束:" + DateTime.Now.ToString());            Console.ReadLine();        }