多线程之异步编程: 经典和最新的异步编程模型,async与await-白红宇

多线程之异步编程: 经典和最新的异步编程模型,async与await

阅读量：7250 次

发布时间：2019-06-29

本文共 8798 字，大约阅读时间需要 29 分钟。

经典的异步编程模型（IAsyncResult）

最新的异步编程模型（async 和 await）

将 IAsyncInfo 转换成 Task

将 Task 转换成 IAsyncInfo

示例

1、使用经典的异步编程模型（IAsyncResult）实现一个支持异步操作的类

Thread/Async/ClassicAsync.cs

/* * 使用经典的异步编程模型（IAsyncResult）实现一个支持异步操作的类 */using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading;using System.Threading.Tasks;namespace XamlDemo.Thread.Async{    public class ClassicAsync    {        private delegate string HelloDelegate(string name);        private HelloDelegate _helloDelegate;        public ClassicAsync()        {            _helloDelegate = new HelloDelegate(Hello);        }        private string Hello(string name)        {            new ManualResetEvent(false).WaitOne(3000);            return "hello: " + name;        }        // begin 方法        public IAsyncResult BeginRun(string name, AsyncCallback callback, Object state)        {            // 新开线程，去执行 Hello() 方法，callback 是回调，state 是上下文            return _helloDelegate.BeginInvoke(name, callback, state);        }        // end 方法        public string EndRun(IAsyncResult ar)        {            if (ar == null)                throw new NullReferenceException("IAsyncResult 不能为 null");            return _helloDelegate.EndInvoke(ar);        }    }}

Thread/Async/ClassicAsyncDemo.xaml

Thread/Async/ClassicAsyncDemo.xaml.cs

/* * 演示如何通过经典的异步编程模型（IAsyncResult）来进行异步操作 *  * IAsyncResult - 异步操作结果 *     AsyncState - 上下文 *     IsCompleted - 异步操作是否已完成 *     AsyncWaitHandle -  获取用于等待异步操作完成的 System.Threading.WaitHandle 对象（通过 WaitHandle.WaitOne() 在当前线程等待） */using System;using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;namespace XamlDemo.Thread.Async{    public sealed partial class ClassicAsyncDemo : Page    {        System.Threading.SynchronizationContext _syncContext;        public ClassicAsyncDemo()        {            this.InitializeComponent();            // 获取当前 UI 线程            _syncContext = System.Threading.SynchronizationContext.Current;        }        private void btnIAsyncResult_Click_1(object sender, RoutedEventArgs e)        {            ClassicAsync classicAsync = new ClassicAsync();            IAsyncResult ar = classicAsync.BeginRun("webabcd", new AsyncCallback(Callback), classicAsync);            lblMsg.Text = "开始执行，3 秒后完成";        }        private void Callback(IAsyncResult ar)        {            ClassicAsync classicAsync = (ClassicAsync)ar.AsyncState;            string result = classicAsync.EndRun(ar);            _syncContext.Post(                (ctx) =>                {                    lblMsg.Text = result;                },                null);        }    }}

2、演示如何通过最新的异步编程模型（async 和 await）来进行异步操作

Thread/Async/NewAsyncDemo.xaml

Thread/Async/NewAsyncDemo.xaml.cs

/* * 演示如何通过最新的异步编程模型（async 和 await）来进行异步操作 *  * 注： * 1、要想 await，其所在方法必须标记为 async * 2、方法被标记为 async 是为了让编译器重新编写该方法，使 await 中的内容重新编写为具有 GetAwaiter() 等实际异步逻辑的代码 */using System;using System.Threading;using System.Threading.Tasks;using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;namespace XamlDemo.Thread.Async{    public sealed partial class NewAsyncDemo : Page    {        private static int _count = 0;        public NewAsyncDemo()        {            this.InitializeComponent();        }        // 不带返回值的 Task        private async Task TaskWithoutReturn()        {            // 在另一个线程 sleep 1000 毫秒，然后回到 UI 线程            await Task.Delay(1000);            // await Task.Delay(Timeout.Infinite); 长眠于此            // await Task.Delay(Timeout.InfiniteTimeSpan); 长眠于此            // 直接在当前线程 sleep 可以使用如下方法，因为 WinRT 中没有 Thread.Sleep() 了            // new ManualResetEvent(false).WaitOne(1000);            Interlocked.Increment(ref _count);        }        // 带返回值的 Task        private async Task
     
       TaskWithReturn()        {            await Task.Delay(1000);            Interlocked.Increment(ref _count);            return _count;        }        // 演示不带返回值的异步操作        private async void btnTaskWithoutReturn_Click_1(object sender, RoutedEventArgs e)        {            // ConfigureAwait(false) - 异步操作后不返回 UI 线程，可节省一点点资源。默认值：ConfigureAwait(true)            await TaskWithoutReturn().ConfigureAwait(false);            lblMsg.Text = "count: " + _count.ToString();        }        // 演示带返回值的异步操作        private async void btnTaskWithReturn_Click_1(object sender, RoutedEventArgs e)        {            int result = await TaskWithReturn();            lblMsg.Text = "count: " + result.ToString();        }        // 演示多任务并行执行的异步操作        private async void btnMultiTask_Click_1(object sender, RoutedEventArgs e)        {            Task task = Task.WhenAll(TaskWithoutReturn(), TaskWithoutReturn(), TaskWithoutReturn());            DateTime dt = DateTime.Now;            await task;            lblMsg.Text = "count: " + _count.ToString() + ", 执行时间: " + (DateTime.Now - dt).TotalSeconds.ToString() + "秒";        }        // 演示如何执行一个不 await 的 Task        private void btnTaskWithoutAwait_Click_1(object sender, RoutedEventArgs e)        {            // 让 task 在新线程执行去吧，本线程不管它是什么执行情况            Task task = TaskWithoutReturn();            lblMsg.Text = "count: " + _count.ToString();        }    }}

3、演示如何将 IAsyncInfo（IAsyncAction, IAsyncOperation, IAsyncActionWithProgress, IAsyncOperationWithProgress）转成 Task

Thread/Async/IAsyncInfo2Task.xaml

Thread/Async/IAsyncInfo2Task.xaml.cs

/* * 演示如何将 IAsyncInfo（IAsyncAction, IAsyncOperation, IAsyncActionWithProgress, IAsyncOperationWithProgress） 转成 Task */using System;using System.Runtime.InteropServices.WindowsRuntime;using System.Threading;using System.Threading.Tasks;using Windows.Foundation;using Windows.UI.Xaml.Controls;using Windows.UI.Xaml.Navigation;namespace XamlDemo.Thread.Async{    public sealed partial class IAsyncInfo2Task : Page    {        public IAsyncInfo2Task()        {            this.InitializeComponent();        }        protected async override void OnNavigatedTo(NavigationEventArgs e)        {            // 用于取消 Task            CancellationTokenSource cts = new CancellationTokenSource();            // 创建一个 IAsyncInfo            IAsyncOperation
     
       action = AsyncInfo.Run
      
       (               (token) =>                   Task.Run
       
        (                       () =>                       {                           token.WaitHandle.WaitOne(3000);                           token.ThrowIfCancellationRequested();                           return 10 * 10;                       },                       token));            lblMsg.Text = "开始执行，3 秒后完成";            // 将 IAsyncOperation 转换成 Task            // AsTask() 是扩展方法，其逻辑在 System.WindowsRuntimeSystemExtensions 类中            Task
        
          task = action.AsTask
         
          (cts.Token);            int result = await task;            lblMsg.Text = "结果：" + result.ToString();        }    }}

4、演示如何将 Task 转成 IAsyncInfo（IAsyncAction, IAsyncOperation）

Thread/Async/Task2IAsyncInfo.xaml

Thread/Async/Task2IAsyncInfo.xaml.cs

/* * 演示如何将 Task 转成 IAsyncInfo（IAsyncAction, IAsyncOperation） */using System;using System.Threading;using System.Threading.Tasks;using Windows.Foundation;using Windows.UI.Xaml.Controls;using Windows.UI.Xaml.Navigation;namespace XamlDemo.Thread.Async{    public sealed partial class Task2IAsyncInfo : Page    {        public Task2IAsyncInfo()        {            this.InitializeComponent();        }        protected async override void OnNavigatedTo(NavigationEventArgs e)        {            // 用于取消 IAsyncInfo（注意：本例中的 IAsyncInfo 是从 Task 转换过来的，所以 IAsyncInfo.Cancel() 方法无效）            CancellationTokenSource cts = new CancellationTokenSource();            // 创建一个 Task            Task
     
       task = Task.Run
      
       (                () =>                {                    cts.Token.WaitHandle.WaitOne(3000);                    cts.Token.ThrowIfCancellationRequested();                    return 10 * 10;                },                cts.Token);            lblMsg.Text = "开始执行，3 秒后完成";            // 将 Task 转换成 IAsyncOperation            // AsAsyncAction(), AsAsyncOperation() 是扩展方法，其逻辑在 System.WindowsRuntimeSystemExtensions 类中            IAsyncOperation
       
         operation = task.AsAsyncOperation
        
         ();            int result = await operation;            lblMsg.Text = "结果：" + result.ToString();                   }    }}