F# FusionTasks

Status

	main	devel
NuGet Package
Continuous integration

---

What is this?

• F# Async workflow <--> .NET Task/ValueTask easy seamless interoperability library.
• Sample code (F# side):

let asyncTest = async {
  use ms = new MemoryStream()

  // FusionTasks directly interpreted System.Threading.Tasks.Task class in F# async-workflow block.
  do! ms.WriteAsync(data, 0, data.Length)
  do ms.Position <- 0L

  // FusionTasks directly interpreted System.Threading.Tasks.Task<T> class in F# async-workflow block.
  let! length = ms.ReadAsync(data2, 0, data2.Length)
  do length |> should equal data2.Length
}

• Sample code (C# side):

using System.Threading.Tasks;
using Microsoft.FSharp.Control;

public async Task AsyncTest(FSharpAsync<int> asyncIntComp)
{
  // FusionTasks simple usage F#'s Async<unit> direct awaitable.
  await FSharpAsync.Sleep(500);
  Console.WriteLine("Awaited F# async function (unit).");

  // FusionTasks simple usage F#'s Async<int> direct awaitable.
  var result = await asyncIntComp;
  Console.WriteLine("Awaited F# async function: Result=" + result);
}

---

Features

• Easy interoperable .NET Task/ValueTask <--> F#'s Async.
• F# async workflow block now supports directly .NET Task/ValueTask handle with let!, do! and use!.
• .NET (C# async-await) now supports directly F#'s Async.
• SyncronizationContext capture operation support (F#: AsyncConfigure method / .NET (C#) AsAsyncConfigured method)
• .NET now supports standard asynchronous sequence called IAsyncEnumerable<T>, FusionTasks supports it with for expression.

Benefits

• Easy interoperability, combination and relation standard .NET OSS packages using Task/ValueTask and F#'s Async.
• F# 6.0/4.5 with .NET 6.0/5.0, .NET Core 3.0/2.0 (or higher), .NET Standard 1.6/2.0 and .NET Framework 4.5/4.6.1/4.8.
• Ready to LINQPad 5.

---

Environments

• F# 6.0 or higher/4.5
• .NET 6.0
• .NET 5.0
• .NET Core 3.0/2.0 or higher
• .NET Standard 1.6/2.0/2.1
• .NET Framework 4.5/4.6.1/4.8

Combination chart:

.NET BCL	F#	Details
.NET 6.0	F# 6.0 or higher
.NET 5.0	F# 6.0 or higher
.NET Core 3.1, 3.0	F# 6.0 or higher	(3.0 is deprecated)
.NET Core 2.,2 2.1, 2.0	F# 6.0 or higher	(2.0 is deprecated)
.NET Standard 2.1, 2.0	F# 6.0 or higher
.NET Standard 1.6	F# 4.5
.NET Framework 4.8, 4.6.1	F# 6.0 or higher
.NET Framework 4.5	F# 4.5

---

How to use

• Search NuGet package and install "FSharp.Control.FusionTasks".
• F# use, autoopen'd namespace "FSharp.Control". "System.Threading.Tasks" is optional.
• C# use, using namespace "System.Threading.Tasks". "Microsoft.FSharp.Control" is optional.

Samples

Basic async workflow:

let asyncTest = async {
  use ms = new MemoryStream()

  // FusionTasks directly interpreted System.Threading.Tasks.Task class in F# async-workflow block.
  // Sure, non-generic Task mapping to Async<unit>.
  do! ms.WriteAsync(data, 0, data.Length)
  do ms.Position <- 0L

  // FusionTasks directly interpreted System.Threading.Tasks.Task<T> class in F# async-workflow block.
  // Standard usage, same as manually used Async.AwaitTask.
  let! length = ms.ReadAsync(data2, 0, data2.Length)
  do length |> should equal data2.Length
}

Without async workflow:

use ms = new MemoryStream()

// Manually conversion by an operator "Async.AsAsync" : Task<T> --> Async<'T>
let asy = ms.ReadAsync(data, 0, data.Length) |> Async.AsAsync
let length = asy |> Async.RunSynchronosly

Without async workflow (CancellationToken):

use ms = new MemoryStream()
let cts = new CancellationTokenSource()

// Produce with CancellationToken:
// TIPS: FusionTasks cannot handle directly CancellationToken IN ASYNC WORKFLOW.
//   Because async workflow semantics implicitly handled CancellationToken with Async.DefaultCancellationToken, CancellationToken and CancelDefaultToken().
//   (CancellationToken derived from Async.StartWithContinuations() in async workflow.)
let asy = ms.ReadAsync(data, 0, data.Length).AsAsync(cts.Token)
let length = asy |> Async.RunSynchronosly

Handle Task.ConfigureAwait(...) (Capture/release SynchContext):

let asyncTest = async {
  use ms = new MemoryStream(...)

  // We can use ConfigureAwait() on let!/do!.
  let! length = ms.ReadAsync(data, 0, data.Length).ConfigureAwait(false)
}

NOTE: Older released contains AsyncConfigure(bool) method, but it was obsoleted. Because it existed for avoiding PCL strange linking errors.

Delegate async continuation - works like TaskCompletionSource<T>:

open System.Threading

let asyncCalculate() =
  // Create AsyncCompletionSource<'T>.
  let acs = new AsyncCompletionSource<int>()

  // Execution with completely independent another thread...
  let thread = new Thread(new ThreadStart(fun _ ->
    Thread.Sleep(5000)
    // If you captured thread context (normally continuation or callbacks),
    // can delegation async continuation using AsyncCompletionSource<'T>.
    acs.SetResult(123 * 456)))
  thread.Start()

  // Async<'T> instance
  acs.Async

Standard asynchronous sequence IAsyncEnumerable<T>:

let asyncTest = async {
  // FusionTasks directly interpreted System.Collection.Generic.IAsyncEnumerable<T> in
  // F# async-workflow for expression.
  for value in FooBarAccessor.EnumerableAsync() do
    // Totally asynchronous operation in each asynchronous iteration:
    let! result = value |> FooBarCollector.calculate
    do! output.WriteAsync(result)

  // ... (Continuation is asynchronously behind `for` loop)
}

And, we can use IAsyncEnumerable<T>.ConfigureAwait(bool) on it.

NOTE: IAsyncEnumerable<T> is supported only these environments:

• net461 or higher.
• netstandard2.0 or higher.
• netcoreapp2.1 or higher.

It limitation comes from NuGet Microsoft.Bcl.AsyncInterfaces 5.0.0.

Standard asynchronous disposer IAsyncDisposable:

let asyncTest = async {
  // FusionTasks directly interpreted System.IAsyncDisposable in
  // F# async-workflow use expression.
  // TIP: We can use `use` expression instead of `use!`,
  // Because the `use!` will be bound asynchronously BEFORE calling `DisposeAsync()`.
  use accessor = DatabaseAccessor.getAsyncDisposableAccessor()

  // (Use accessor...)

  // (Will be disposed asynchronously, calls `DisposeAsync()` at end of scope...)
}

TIPS: We have to add annotation for arguments if using it in async workflow:

let asyncInner arg0 = async {
  // Cause FS0041:
  //   A unique overload for method 'Source' could not be determined based on type information prior to this program point.
  //   A type annotation may be needed.
  //  --> Because F# compiler conflict arg0 type inferences: Async<int> or Task<int>.
  let! result = arg0
  let calculated = result + 1
  printfn "%d" calculated
}

// Fixed with type annotation Async<'T> or Task<'T>:
let asyncInner (arg0:Async<_>) = async {
  let! result = arg0
  let calculated = result + 1
  printfn "%d" calculated
}

In C# side:

• Really need sample codes? huh? :)

---

Easy LINQPad 5 driven:

• Before setup NuGet package (FSharp.Control.FusionTasks) the LINQPad NuGet Manager.

open System.IO

// Result is Async<byte[]>
let asyncSequenceData =
  let r = new Random()
  let data = [| for i = 1 to 100 do yield byte (r.Next()) |]
  async {
    use fs = new MemoryStream()
    do! fs.WriteAsync(data, 0, data.Length)
    do! fs.FlushAsync()
    return fs.ToArray()
  }

// Convert to Task<byte[]> and dump:
asyncSequenceData.AsTask().Dump()

---

"task-like" and ValueTask appendix

• .NET add new "task-like" type. "task-like" means applied a attribute "System.Runtime.CompilerServices.AsyncMethodBuilderAttribute" and declared the async method builder.
• ValueTask overview:
  • New standard "task-like" type named for "ValueTask<T>" for C#. FusionTasks supported ValueTask<T> on 1.0.20.
  • ValueTask<T> declared by struct (Value type) for goal is improvement performance. But this type has the Task<T> instance inside and finally continuation handle by Task<T>.
  • ValueTask<T> performance effective situation maybe chatty-call fragments using both caller C# and awaiter C# code...
  • ValueTask<T> a little bit or no effect improvement performance, because usage of senario for FusionTasks.
• "task-like" augumenting is difficult:
  • We have to apply to task-like type with the attribute "AsyncMethodBuilderAttribute".
  • Means if already declared type (Sure, we have FSharpAsync<'T>) cannot augument and cannot turn to task-like type.
  • Therefore cannot directly return for FSharpAsync<'T> from C#'s async-await method.
  • And cannot auto handle task-like type by FusionTasks, because no type safe declaration for task-like type...
    • For example, if force support task-like type, FusionTasks require augument "Source: taskLike: obj -> FSharpAsync<'T>" overload on FSharpAsync<'T>. This cannot type safe.
• Conclusion:
  • So FusionTasks support only "ValueTask<T>" type and cannot support any other "task-like" types.

Additional resources

• Source codes available only "FSharp.Control.FusionTasks" folder.
• The slides: "How to meets Async and Task" in Seattle F# Users group "MVP Summit Special: A Night of Lightning Talks" 2016.11.09 http://www.slideshare.net/kekyo/asyncs-vs-tasks

<iframe src="https://www.slideshare.net/slideshow/embed_code/68424602" width="800" height="500" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"></iframe>

TODO

Improvements more easier/effective interfaces.

---

License

• Copyright (c) 2016-2022 Kouji Matsui (@kozy_kekyo)
• Under Apache v2 http://www.apache.org/licenses/LICENSE-2.0

History

• 2.6.0:
  • Final version. Thank you using FusionTasks!
  • You are ready to use both FusionTasks and F# 7.0! See issue #14.
  • Added supporting .NET Core 2.2 environments.
  • Minimized package dependency.
• 2.5.0:
  • Supported .NET 6.0 and F# 6.0 environment.
• 2.4.0:
  • Supported varies for operator Async.AsAsync.
  • Completed supporting configured capturing context method ConfigureAwait(bool) on all Task based instances.
• 2.3.3:
  • Supported .NET asynchronous disposer (IAsyncDisposable).
  • Supported releasing synchronization context by IAsyncEnumerable<T>.ConfigureAwait(bool).
  • Fixed minor exception leaking at the continuation for asynchronous sequence.
• 2.3.0:
  • Supported .NET asynchronous sequence (IAsyncEnumerable and essential types).
• 2.2.0:
  • Suppressed Task/ValueTask allocation when they were already completed (#12, @danielmarbach)
• 2.1.1:
  • Downgraded FSharp.Core requirements from 5.0.1 to 5.0.0.
• 2.1.0:
  • Added .NET 5, .NET Core 3 and .NET Framework 4.8 assemblies.
  • Fixed capturing synchronization context at the asynchronous continuations.
• 2.0.2:
  • Fixed add xml comments into package.
• 2.0.1:
  • Add support ValueTask for non-generic version.
  • Fixed XML comments.
• 2.0.0:
  • Supported F# 4.5, .NET Standard 2.0 and .NET Core 2.0.
  • Sorry, archived all PCL's libraries. Now FusionTasks supports only .NET Framework 4.5, .NET Core 2.0 and .NET Standard 1.6/2.0.
  • Solution structure refablished. Changed to .NET Core modern-style.
• 1.1.1:
  • Add ValueTask<'T> bind source overload.
• 1.1.0:
  • Supported F# 4.1 and .NET Standard 1.6. (Unfortunately deprecated FS40.netcore (netstandard1.4) package, try to migrate to F# 4.1 :)
• 1.0.20:
  • Support ValueTask<T> (Exclude net40 and Profile 47 platform, added dependency for System.Threading.Tasks.Extensions).
  • Update version for .NET Core F# (1.0.0-alpha-161205).
• 1.0.13:
  • Reduce to only contains .NET Core's assembly in FS40.netcore package.
  • Refactor folder structures.
• 1.0.12:
  • Add .NET Core support (Separated package: FSharp.Control.FusionTasks.FS40.netcore with -Pre option required)
• 1.0.2:
  • Support 'for .. in' expressions. (Thx Armin!)
• 1.0.1:
  • Fixed cause undefined Async<'T> using combination Async<'T> and Task/Task<T> in async workflow. (Thx Honza!)
• 1.0.0:
  • RTM release 👏
  • Add FSharp.Core NuGet references.
  • Temporary disable support .NET Core. If reached F# RTM, continue development... (PR welcome!!)
  • Add sample codes.
• 0.9.6:
  • WIP release.
• 0.9.5:
  • WIP release.
• 0.9.4:
  • Fixed nuspec reference System, System.Core
• 0.9.3:
  • Fixed nuspec frameworkAssemblies.
• 0.9.2:
  • Add package targetFramework.
  • Updated RelaxVersioner.
• 0.9.1:
  • Remove strongly-signed (Unit test doesn't work...)
  • Omit synchronizers (AsyncLock, AsyncLazy). Thats moving to FSharp.Control.AsyncPrimitives project (https://github.com/kekyo/FSharp.Control.AsyncPrimitives).
  • Add target dnxcore50 into F# 4.0 (for .NET Core 1.0)
  • Source codes and documents bit changed.
• 0.5.8:
  • Add strongly-signed.
• 0.5.7:
  • Add PCL Profile 7.
• 0.5.6:
  • Add PCL Profile 78.
  • Fixed minor PCL moniker fragments.
• 0.5.5:
  • Fixed version number.
  • Fixed icon image url.
• 0.5.4:
  • Auto open FSharp.Control.
  • Manage AppVeyor CI.
• 0.5.3: Implement awaiter classes.
• 0.5.2: Add dependency assemblies.
• 0.5.1: NuGet package support.