The Evolution of Async Programming on .NET Platform

ZhaoJie @ SNDANov, 2010

About Me

• 赵劼 / 老赵 / Jeffrey Zhao / 赵姐夫

• 日写代码三百行，不辞长做程序员• Blog: http://blog.zhaojie.me/

• Twitter: @jeffz_cn

• F#, Scala, JavaScript, Python, .NET, mono...

• Java (as the language) hater

Agenda

• Why & How

• .NET 1.0

• .NET 2.0 / C# 2.0

• .NET 3.0 / F#

• .NET 4.0 / Reactive Framework

• Future / C# vNext

Why?

Because the essence ofCloud, Web, Mobile

is asynchronous computations

How?

By providing powerful language features / programming model /

libraries

.NET 1.0

Two Raw Async Models

• Begin/End

• Event-based

• Both are callback-based• Which is just “asynchronous” means

Begin/End Async Modeldelegate AsyncCallback(IAsyncResult);

interface IAsyncResult { object AsyncState { get; } WaitHandle AsyncWaitHandle { get; } bool CompletedSynchronously { get; } bool IsCompleted { get; }}

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

TResult EndXxx(IAsyncResult);

Event-based Async Model

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

class Worker { event EventHandler<XxxCompletedArgs> XxxCompleted; void XxxAsync(arg1, arg2, ...);}

Let’s write a “Transfer” method in 4 different

ways

Demo 1

Sync & Async

Code Locality is Broken

• Used to expressing algorithms linearly

• Async requires logical division of algorithms• No if / using / while / for ...

• Very difficult to• Combine multiple asynchronous operations

• Deal with exceptions and cancellation

.NET 2.0 / C# 2.0

“yield” for Iterators

IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2;

}

“yield” for Iterators

IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2;

}

MoveNext()

“yield” for Iterators

IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2;

}

MoveNext()

MoveNext()

“yield” for Iterators

IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2;

}

MoveNext()

MoveNext()

MoveNext()

“yield” for Iterators

IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2;

}

MoveNext()

MoveNext()

MoveNext()

MoveNext()

Demo 2

Async with “yield”

“yield return” for Async

• Coming with new programming patterns

• Keep code locality• Good parts: support if / using / while / for ...

• But not perfect: cannot use try...catch

• The primitives for Fibers - lightweight computation units

.NET 3.0 / F#

F#

• Language by Don Syme, MS Research

• Strongly statically typed language

• Functional language with OO ability

• For industry and education• Open source (Apache 2.0)

• Cross-platform supported by Microsoft

Concurrency Challenges

• Shared State - Immutability

• Code Locality - async { ... }

• I/O Parallelism - async { ... }

• Scaling to Multi-Machine - Agents with async { ... }

What’s 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

Async Workflow

async {   let! res = <async work> ...}

Async Workflow

async {   let! res = <async work> ...}

React!

Async Workflow

async {   let! res = <async work> ...}

React!

an HTTP Responsean UI Event

a Timer Callbacka Query Response

a Web Servcie Responsea Disk I/O Completion

an Agent Message

How async { ... } Worksasync { let! img = AsyncRead "http://..." printfn "loaded!" do! AsyncWrite img @"c:\..." printfn "saved!" }

How async { ... } Worksasync { 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())))))

=

Demo 3

Async in F#

F# Async Workflow• Library, not a language feature• Based on Computation Expressions in F#

• Support all kinds of language constructions• Error handling: try...catch

• Loop: while / for (like “foreach” in C#)

• Others: if / use (like “using” in C#), etc.

• Easy to• Combine multiple asynchronous operations

• Deal with exceptions and cancellation

F# Resourceshttp://fsharp.net

Programming F# Expert F# 2.0 Real World FP

.NET 4.0 / Reactive Framework

Reactive Framework

Fundamentally change the way you think about coordinating and

orchestrating asynchronous and event-based programming

How

By showing that asynchronous and event-base computations are just

push-based collections

Environment

Program

Interactive Reactive

Enumerable Collections

interface IEnumerable<out T> { IEnumerator<T> GetEnumerator();}

interface IEnumerator<out T> { bool MoveNext(); T Current { get; }}

Dualize

Observable Collections

interface IObservable<out T> { IDisposable Subscribe(IObserver<T> o)}

interface IObserver<in T> { void OnCompleted(); void OnNext(T item); void OnError(Exception ex);}

IEnumerable & IEnumerator are prototypical interfaces for interactive collections and interactive programs.

IObservable & IObserver are prototypical interfaces for observable collections and reactive, asynchronous & event-based programs.

LINQ to Observable

If you are writingLINQ or declarative codein an interactive program...

LINQ to Observable

If you are writingLINQ or declarative codein an interactive program...

You already know how to use it!

Again

... 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

Again

... 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

Rx in JavaScript

• A full featured port for JavaScript• Easy-to-use conversions from existing DOM,

XmlHttpRequest, etc

• In a download size of less than 7kb (gzipped)

• Bindings for various libraries / frameworks• jQuery

• MooTools

• Dojo

• ...

Time Flies like an Arrowvar container = $("#container");var mouseMove = container.toObservable("mousemove");

for (var i = 0; i < text.length; i++) { (function(i) { var ele = $("<span/>").text(text.charAt(i)); ele.css({position: "absolute"}).appendTo(container);

mouseMove.Delay(i * 100).Subscribe(function (ev) { ele.css({ left: ev.clientX + i * 20 + 15 + "px", top: ev.clientY + "px" }); });

})(i);

Demo 4

Async with Reactive Fx

Benefits of Rx

• Easy to composite and coordinate async operations

• Express the algorithm in functional ways• Helper method: For / While / If / Try / Switch...

• Easy to be unit tested

• ...

Rx & Language Features

• Features in C# that Rx uses• Extension method

• Lambda expression & closure

• Type inference

• LINQ query expression

• Rx has been implemented in ...• C# & VB

• JavaScript

• F#

Portability

• Rx can be easily ported to various languages• Scala

• Ruby

• Python

• modern languages with basic functional features

• Almost impossible to implement Rx in Java• Cannot extend a type without breaking code

• Missing enough functional features

Rx Resources

• Matthew Podwysocki• http://codebetter.com/blogs/matthew.podwysocki/

• Reactive Framework on MSDN DevLabs• http://msdn.microsoft.com/en-us/devlabs/

ee794896.aspx

• Tomáš Petříček• http://tomasp.net/

Comparison

• F# Async Workflow• Elegant, simple, easy to use

• Can only be used at server-side (WebSharper come to rescure?)

• Reactive Framework• Can be used at both server-side and client-side.

• New async model brings learning cost.

Can we use“Async Workflow”

in JavaScript?

Demo 5

Jscex & Jscex.Async

C# vNext

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;}

Source

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;}

Compiled

Conclusion

• Async Programming is difficult

• New programming language / feature / library / model can help

• JavaScript is incredible.

Q & A

Thanks