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Async, Await 是基于 .NEt 4.5架构的， 用于处理异步，防止死锁的方法的开始和结束, 提高程序的响应能力。比如：

Application area           Supporting APIs that contain async methods

 Web access                    HttpClient , SyndicationClient

 Working with files           StorageFile, StreamWriter, StreamReader, XmlReader

 Working with images       MediaCapture, BitmapEncoder, BitmapDecoder

 WCF programming          Synchronous and Asynchronous Operations

Async, Await 不会产生新的线程。 但是Task.Run 方法就是多线程的。 Asynchronous code is code that returns upon completion. By Task.Run, we can make is a multithreaded.

Take files as an example I encountered today:

        public async Task SendFallMail(string path){
            try
            {
                mail.Subject = subjectFall;
                mail.Body = "Fall down!";

                using (MailMessage ms = mail) {
                    ms.Attachments.Add(new Attachment(path));
                    using (SmtpClient sc = SmtpServer)
                    {
                        Task t = Task.Factory.StartNew(() =>
                        { 
                            sc.Send(ms); 
                        });
                        await t;
                    }
                }
                File.Delete(path);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }

It should wait t which is sending an e-mail wihich attached an picture in path.

Then delete the pic in path, wihch is working properly after I use the using statement...

Without using the using statement, it shows IO exception said: 

Process Cannot Access the file “\Path” because it is being used by some other process

C# Async, Await and using statements

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原文地址：http://www.cnblogs.com/bruceyo/p/4026522.html