The Evolution of Async Programming (GZ TechParty C#)

.NET平台编程语言
异步特性演变
赵劼 - 2012.2

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• 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

内容

• C# 1.0
• C# 2.0
• F#
• C# 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

Begin / End 模型
delegate AsyncCallback(IAsyncResult);

interface IAsyncResult {
object AsyncState { get; }
...
}

void BeginXyz(arg1, arg2, ..., AsyncCallback, state);

TResult EndXyz(IAsyncResult);

事件模型

class XyzCompletedEventArgs : EventArgs {
Exception Error { get; }
TResult Result { get; }
}

class Target {
event EventHandler<XyzCompletedArgs> XyzCompleted;
void XyzAsync(arg1, arg2, ...);
}

示例⼀一

C# 1.0原生异步编程

The Evolution of Async Programming (GZ TechParty C#)

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

“yield” for Iterators
IEnumerable<int> Numbers() {

yield return 0;

yield return 1;

yield return 2;

}

MoveNext()
yield return 0;

yield return 1;

yield return 2;

}

MoveNext()
yield return 0;

MoveNext()
yield return 1;

yield return 2;

}

MoveNext()
yield return 0;

MoveNext()
yield return 1;

MoveNext()
yield return 2;

}

MoveNext()
yield return 0;

MoveNext()
yield return 1;

MoveNext()
yield return 2;
MoveNext()
}

示例二

C# 2.0的yield异步编程

“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

F# 编程语言
• 微软研究院Don Syme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

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

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

异步工作流
async {
let! res = <async work>
...
}

异步工作流
React!
async {
...
}

异步工作流
React!
async {
...
}
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

async { ... } 工作方式
async {
let! img = AsyncRead "http://..."
printfn "loaded!"
do! AsyncWrite img @"c:..."
printfn "saved!" }

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())))))

源代码

async Task<XElement> GetRssAsync(string url) {
var client = new WebClient();
var task = client.DownloadStringTaskAsync(url);
var text = await task;
var xml = XElement.Parse(text);
return xml;
}

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;
}

示例四

C# 5 异步编程支持

示例五

Jscex：JS异步编程

The Evolution of Async Programming (GZ TechParty C#)

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