How to meets Async and Task

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Information about How to meets Async and Task

Published on November 8, 2016

Author: kekyo



2. 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

3. Agenda Continuation Passing Style .NET Task / async-await / F# Async workflow Continuation Linking

4. 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

5. Continuation Passing Style Continuation function passing to argument Continuation implement with nested lambda expressions… Standard direct style

6. Continuation Passing Style (Details) Continuation-Passing style Continuation implementation nearly equals “Callback”

7. Continuation Passing Style (Details) The callback technics likely async continuation handler in JavaScript. Continuation-Passing style Don’t worry!! This technics naming “CPS!!”

8. Continuation Passing Style Understand CPS?

9. Agenda Continuation Passing Style .NET Task / async-await / F# Async workflow Continuation Linking

10. 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?

11. .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

12. .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

13. .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)

14. 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?

15. 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>.

16. 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?

17. Agenda Continuation Passing Style .NET Task / async-await / F# Async workflow Continuation Linking

18. 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().

19. 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#.

20. Senario for .NET Task / C# side: Can directly awaitable for Async<int>. C# compiler invoking GetAwaiter function.

21. 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.

22. Senario for F# Async workflow side: Can directly awaiting for Task<int>. F# compiler translate calling “Source” function.

23. 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.

24. 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) ◦

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