C# .Net学习笔记—— 异步和多线程（await/async）

一、介绍

1、控制台测试await/async

2、C# 5.0 .Net framework4.5 CLR4.0 以后才有，本身是一种语法糖

二、基本测试

1、不加await测试。

        private async static Task TestAsync() {Log.Info($"当前主线程id={Thread.CurrentThread.ManagedThreadId}");NoReturnNoAwait();for (int i = 0; i < 10; i++){Thread.Sleep(300);Log.Info($"Main Thread Task ManagedThreadID = {Thread.CurrentThread.ManagedThreadId}");}}private static async void NoReturnNoAwait() {Log.Info($"NoReturn Sleep before await,ThreadID={Thread.CurrentThread.ManagedThreadId}");TaskFactory taskFactory = new TaskFactory();Task task = taskFactory.StartNew(() =>{Log.Info($"NoReturn Sleep before,ThreadID={Thread.CurrentThread.ManagedThreadId}");Thread.Sleep(3000);Log.Info($"NoReturn Sleep after,ThreadID={Thread.CurrentThread.ManagedThreadId}");});Log.Info($"NoReturn Sleep after await,ThreadID={Thread.CurrentThread.ManagedThreadId}");}

2、加await测试。

        private async static Task TestAsync() {Log.Info($"当前主线程id={Thread.CurrentThread.ManagedThreadId}");NoReturn();//NoReturnNoAwait();for (int i = 0; i < 10; i++){Thread.Sleep(300);Log.Info($"Main Thread Task ManagedThreadID = {Thread.CurrentThread.ManagedThreadId}");}}private static async void NoReturn() {Log.Info($"NoReturn Sleep before await,ThreadID={Thread.CurrentThread.ManagedThreadId}");TaskFactory taskFactory = new TaskFactory();Task task = taskFactory.StartNew(() => {Log.Info($"NoReturn Sleep before,ThreadID={Thread.CurrentThread.ManagedThreadId}");Thread.Sleep(3000);Log.Info($"NoReturn Sleep after,ThreadID={Thread.CurrentThread.ManagedThreadId}");});await task;  //主线程到这里就返回了，执行主线程任务Log.Info($"NoReturn Sleep after await,ThreadID={Thread.CurrentThread.ManagedThreadId}");}

结果：从打印出来的两种执行顺序来看，加了await以后，主线程运行到await这行就会执行
回主线程任务。而await后面的代码将由主线程或其他线程来执行

原理：await后面的代码，会被封装成委托，在await task之后成为回调（编译器功能，状态机实现），这个回调的线程是不确定的，可能是主线程，可能是子线程也可能是其他线程。

它可以等价于task.ContinueWith(t=>{}) 这里包起来

验证一下：
       private async void AwaitTest() {//方法一：NoReturn();//方法二：TaskFactory taskFactory = new TaskFactory();Task task = taskFactory.StartNew(() =>{Log.Info($"NoReturn Sleep before,ThreadID={Thread.CurrentThread.ManagedThreadId}");Thread.Sleep(3000);Log.Info($"NoReturn Sleep after,ThreadID={Thread.CurrentThread.ManagedThreadId}");});task.ContinueWith(t =>{callBack();});await task;}private static async void NoReturnNoAwait(){Log.Info($"NoReturn Sleep before await,ThreadID={Thread.CurrentThread.ManagedThreadId}");TaskFactory taskFactory = new TaskFactory();Task task = taskFactory.StartNew(() =>{Log.Info($"NoReturn Sleep before,ThreadID={Thread.CurrentThread.ManagedThreadId}");Thread.Sleep(3000);Log.Info($"NoReturn Sleep after,ThreadID={Thread.CurrentThread.ManagedThreadId}");});Log.Info($"NoReturn Sleep after await,ThreadID={Thread.CurrentThread.ManagedThreadId}");}private void callBack(){Log.Info($"我是一个回调。。");Log.Info($"NoReturn Sleep after await,ThreadID={Thread.CurrentThread.ManagedThreadId}");}

三、返回值问题

1、不需要传值的时候，我们返回值就写成Task或者void都可以

2、需要传值的话 ，可以使用这种带泛型传值

四、小案例

       private void MainThread() {Log.Info("主线程Start");Async();Log.Info($"aaa {Thread.CurrentThread.ManagedThreadId.ToString("00")}");}private async void Async(){Log.Info($"ddd {Thread.CurrentThread.ManagedThreadId.ToString("00")}");await Task.Run(() =>{Thread.Sleep(500);Log.Info($"bbb {Thread.CurrentThread.ManagedThreadId.ToString("00")}");});Log.Info($"ccc {Thread.CurrentThread.ManagedThreadId.ToString("00")}");}