How to meetsAsync and Task2016.11.08 MVP SUMMIT SPECIAL: A NIGHT OF LIGHTNING TALKS KOUJI MATSUI (@KEKYO2)

Kouji Matsui - kekyo• NAGOYA city, AICHI pref., JP

• Twitter – @kekyo2 / Facebook

• ux-spiral corporation

• Microsoft Most Valuable Professional VS and DevTech 2015-

• Certified Scrum master / Scrum product owner

• Center CLR organizer.

• .NET/C#/F#/IL/metaprogramming or like…

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Agenda

Continuation Passing Style

.NET Task / async-await / F# Async workflow

Continuation Linking

Continuation Passing Style

Continuation-passing style (CPS) is a style of programming in which control is passed explicitly in the form of a continuation.

“continuation-passing style” - Wikipedia

Continuation Passing Style

Continuation function passing to argument

Continuation implement withnested lambda expressions…

Standard direct style

Continuation Passing Style (Details)

Continuation-Passing style

Continuation implementationnearly equals “Callback”

Continuation Passing Style (Details)

The callback technics likely async continuation handler in JavaScript.

Continuation-Passing style

Don’t worry!!This technics naming “CPS!!”

Continuation Passing Style

Understand CPS?

Agenda

Continuation Passing Style

.NET Task / async-await / F# Async workflow

Continuation Linking

The keyword: .NET Task

The “Task” control interface in .NET 4.0.

In .NET 4.5 with C# 5.0, Task can handle in “async-await” style.

What relationship

between Task and CPS?

.NET Task (In .NET 4.0 / C# 4.0)

.NET 4.0 Task is using with ContinueWith function.

Continuation passing into Task.ContinueWith()--> likely CPS

.NET Task (In .NET 4.5/C# 5.0)

And in .NET 4.5/C# 5.0 with “async-await” style:

That means “Continuation” OK?

Using Task with async-await

.NET Task comparison

So, the continuation in async-await:

Means CPS for “async-await” syntax sugar.

In .NET 4.0 (C# 4.0 Task only) And .NET 4.5 (C# 5.0 async-await)

F# Async workflow

Async workflow supported from F# 2.0.

Integrated seamless async handling into F# syntax (In .NET 2.0)

What relationship

between Async and CPS?

F# Async workflow

Structure nearly equals “async-await.”That’s CPS?

Returned Async<‘T> type

※ let! (Let-Bang) is awaiting for Async<‘T>, and bound ‘T value.Means C#’s await keyword.

※ If continuation implement in F# Async workflow, use Async.FromContinuations<‘T>.

Overall Async implementations

.NET Task : using ContinueWith

.NET Task : using async-await

F# Async workflow : using let!

Both all patterns nearly with Continuation-Passing style?

Agenda

Continuation Passing Style

.NET Task / async-await / F# Async workflow

Continuation Linking

Connection both continuations

Can I connect by seamless between .NET Tasks and F# Asyncs?◦ Before thinking, very nearly structure and interfaces for Task<T> and Async<‘T>.

Then?◦ Can use await in C# for F#’s Async<‘T>?

◦ And/or can use let! in F# async workflow for Task<T>?◦ If can, use let!, use!, do!, return! handling directly with HttpClient.GetStreamAsync().

Senario for .NET Task / C# side:

Declare augumented function “AsTask” on Async<‘T> class.Can conversion from Async<‘T> to Task<T>.◦ Use Async.StartWithContinuations<T> function:

Manipulate “TaskCompletionSource<T> class” (Handled SetResult, SetException and SetCanceled functions) and returns Task<T>.

Implements Async<‘T>.GetAwaiter function (Augumented).◦ Can directly awaitable for Async<‘T> in C#.

Senario for .NET Task / C# side:

Can directly awaitable for Async<int>.C# compiler invoking GetAwaiter function.

Senario for F# Async workflow side:

Declare augumented function “AsAsync” on Task<T> class.Can conversion from Task<T> to Async<‘T>.◦ Use Async.FromContinuations<T> function:

Manipulate Async<‘T> functions from Task.ContinueWith function’s callbacks.

And declare augumented function “Source” on AsyncBuilder<‘T> class.◦ Source function argument is “Task<T>” type and convet to Async<‘T>,

then can use directly let!, use!, do! and return! for Task<T> in F# Async workflow.

Senario for F# Async workflow side:

Can directly awaiting for Task<int>.F# compiler translate calling “Source” function.

Other tips:Conversion both System.Void and FSharp.Unit in type-safer:◦ If awaiting for Async<unit> in C#, cannot receive result value (void).

◦ If using Task (Non-generic) in F# async workflow, can only do! expression.

Support the “CancellationToken”:◦ .NET Task is explicitly handling CancellationToken (ex: argument received).

F# Async workflow is implicitly handling CancellationToken (Async.DefaultCancellationToken).

◦ --> Add CancellationToken argument for AsTask/AsAsync functions.

Don’t use Async.RunSynchronous function:◦ If use RunSynchronous function, will be hard-blocked current thread nearly invoking Task.Wait.

Implements using for Async.FromContinuations<‘T> or Async.StartWithContinuations<‘T>.

Implement new type “AsyncCompletionSource<‘T>”:◦ Async.FromContinuations<T> function handle diffecults (by callback structure) for internal impls.

I want to delegation-based interface likely “TaskCompletionSource<T>” class.

Thanks join!The implementations --> GitHub: FusionTasks◦ https://github.com/kekyo/FSharp.Control.FusionTasks◦ https://www.nuget.org/packages/FSharp.Control.FusionTasks.FS40/

Progressing:◦ FusionTasks (for .NET Core waiting for F# RTM :) Adjusting PCL profiles :(◦ fscx (F# expandable compiler project) https://github.com/fscx-projects/◦ RelaxVersioner (Git based very easy versioner)

https://github.com/kekyo/RelaxVersioner/

My blog (Sorry default language in Japanese)◦ http://www.kekyo.net/