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The Evolution of Async Programming (GZ TechParty C#)
- 1. .NET平台编程语言 异步特性演变 赵劼 - 2012.2
- 2. 关于我 • 赵劼 /老赵 / Jeffrey Zhao / 赵姐夫 • 日写代码三百行，不辞长作程序员 • 博客：http://blog.zhaojie.me/ • 微博：@老赵 • F#, JavaScript, Scala, C#, Python, .NET, Mono... • 痛恨Java语言
- 3. 内容 • C# 1.0 •C# 2.0 • F# • C# 5
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- 5. 两种简单模型 • Begin /End 模型 • 事件模型 • 两种模型都基于回调函数 • “异步”所在
- 6. Begin / End模型 delegate AsyncCallback(IAsyncResult); interface IAsyncResult { object AsyncState { get; } ... } void BeginXyz(arg1, arg2, ..., AsyncCallback, state); TResult EndXyz(IAsyncResult);
- 7. 事件模型 class XyzCompletedEventArgs :EventArgs { Exception Error { get; } TResult Result { get; } } class Target { event EventHandler<XyzCompletedArgs> XyzCompleted; void XyzAsync(arg1, arg2, ...); }
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- 11. 破坏了代码的局部性 • 线性代码表达更清晰，更符合习惯 • 异步会强迫拆分代码逻辑 • 不能使用 if / using / while / for ... • 难以 • 组合异步操作 • 异常处理 • 取消操作
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- 13. “yield” for Iterators IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2; }
- 14. “yield” for Iterators IEnumerable<int> Numbers() { MoveNext() yield return 0; yield return 1; yield return 2; }
- 15. “yield” for Iterators IEnumerable<int> Numbers() { MoveNext() yield return 0; MoveNext() yield return 1; yield return 2; }
- 16. “yield” for Iterators IEnumerable<int> Numbers() { MoveNext() yield return 0; MoveNext() yield return 1; MoveNext() yield return 2; }
- 17. “yield” for Iterators IEnumerable<int> Numbers() { MoveNext() yield return 0; MoveNext() yield return 1; MoveNext() yield return 2; MoveNext() }
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- 19. “yield” 之与异步编程 • 带来新的异步编程模式 •保持代码局部性 • 优势：支持 if / using / while / for ... • 不完美：不支持 try...catch • 可用来实现 Fibers：轻量的计算单元
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- 21. F# 编程语言 • 微软研究院DonSyme设计 • 强类型，静态类型 • 函数式编程语言，包含面向对象特性 • 面向业界及教育 • 开源（Apache 2.0） • 微软提供跨平台支持
- 22. 并发的挑战 • 状态共享 -不可变性 • 代码局部性 - async { ... } • I/O并行 - async { ... } • 扩展至集群 - 使用 async { ... } 的代理
- 23. 什么是 async {... } ... the principle we go by is, don't expect to see a particular concurrency model put into C# because there're many different concurrency model ... it's more about finding things are common to to all kinds of concurrency ... - Anders Hejlsberg
- 24. 异步工作流 async { let! res = <async work> ... }
- 25. 异步工作流 React! async { let! res = <async work> ... }
- 26. 异步工作流 React! async { let! res = <async work> ... } HTTP 响应 UI 事件 Timer 回调 查询结果 Web Servcie 答复 I/O 完成 代理消息
- 27. async { ...} 工作方式 async { let! img = AsyncRead "http://..." printfn "loaded!" do! AsyncWrite img @"c:..." printfn "saved!" }
- 28. async { ...} 工作方式 async { let! img = AsyncRead "http://..." printfn "loaded!" do! AsyncWrite img @"c:..." printfn "saved!" } = async.Delay(fun -> async.Bind(AsyncRead "http://...", (fun img -> printfn "loaded!" async.Bind(AsyncWrite img @"c:...", (fun () -> printfn "saved!" async.Return())))))
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- 31. 源代码 async Task<XElement> GetRssAsync(stringurl) { var client = new WebClient(); var task = client.DownloadStringTaskAsync(url); var text = await task; var xml = XElement.Parse(text); return xml; }
- 32. 编译结果 Task<XElement> GetRssAsync(string url){ var $builder = AsyncMethodBuilder<XElement>.Create(); var $state = 0; TaskAwaiter<string> $a1; Action $resume = delegate { try { if ($state == 1) goto L1; var client = new WebClient(); var task = client.DownloadStringTaskAsync(url); $state = 1; $a1 = task.GetAwaiter(); if ($a1.BeginAwait($resume)) return; L1: var text = $a1.EndAwait(); var xml = XElement.Parse(text); $builder.SetResult(xml); } catch (Exception $ex) { $builder.SetException($ex); } }; $resume(); return $builder.Task; }
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