C# async await 學習筆記1

因爲個人開發工具爲vs.net 2010（.net 4.0)，需先作如下兩步才能進行：

1.下載並安裝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調用的方法須要返回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：

 不知你們注意到，裏面的ThreadId是一致的。

 

 須要注意的是，並非加了async，就是異步了（而是得裏面有調用await方法），例如，下面實際上是同步執行的

 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();
        }