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How to meets​ Async and Task

How to meets​ Async and Task

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


Can use await in C# for F#’s Async?​
And/or can use let! in F# async workflow for Task?​


Microsoft MVP Summit Special: A Night of Lightning Talks in SEATTLE


Kouji Matsui

November 06, 2016


  1. How to meets Async and Task 2016.11.08 MVP SUMMIT SPECIAL:

  2. HELP PLEASE!! I’m hearing and speaking VERY HARD, So try

    to making for CODE AND TECH DRIVEN these slides. Thanks slow down speaking :)
  3. 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… • Bike rider
  4. Agenda Continuation Passing Style .NET Task / async-await / F#

    Async workflow Continuation Linking
  5. 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
  6. Continuation Passing Style Continuation function passing to argument Continuation implement

    with nested lambda expressions… Standard direct style
  7. Continuation Passing Style (Details) Continuation-Passing style Continuation implementation nearly equals

  8. Continuation Passing Style (Details) The callback technics likely async continuation

    handler in JavaScript. Continuation-Passing style Don’t worry!! This technics naming “CPS!!”
  9. Continuation Passing Style Understand CPS?

  10. Agenda Continuation Passing Style .NET Task / async-await / F#

    Async workflow Continuation Linking
  11. 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?
  12. .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
  13. .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
  14. .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)
  15. 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?
  16. 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# Asyncworkflow, use Async.FromContinuations<‘T>.
  17. 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?
  18. Agenda Continuation Passing Style .NET Task / async-await / F#

    Async workflow Continuation Linking
  19. 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().
  20. 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#.
  21. Senario for .NET Task / C# side: Can directly awaitable

    for Async<int>. C# compiler invoking GetAwaiter function.
  22. 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.
  23. Senario for F# Async workflow side: Can directly awaiting for

    Task<int>. F# compiler translate calling “Source” function.
  24. Other tips: Conversion both System.Voidand 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/AsAsyncfunctions. 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.
  25. Thanks join! The implementations --> GitHub: FusionTasks ◦ ◦ Progressing: ◦ FusionTasks (for .NET Core waiting for F# RTM :) Adjusting PCL profiles :( ◦ fscx (F# expandable compiler project) ◦ RelaxVersioner (Git based very easy versioner) My blog (Sorry default language in Japanese) ◦