代理/邮箱处理器在 C# 中使用新的 async/await [英] Agent/MailboxProcessor in C# using new async/await

问题描述

这个问题结合了我不完全理解的两个主题

通读paper 关于 F# 中的异步，我遇到了 Agents/MailboxProcessors 的话题，它可以用来实现反应式状态机.C#5 中新的 async/await 功能是否可以用于在 C# 中实现类似的东西，或者是否已经有类似的东西更适合?

Reading through a paper about async in F#, I came across the topic of Agents/MailboxProcessors, which can be used to implement reactive state machines. Could the new async/await functionality in C#5 be used to implement something similar in C#, or is there already something analogue that would be better suited?

推荐答案

通过一些非常可怕的黑客攻击，您可以使用 async 使用 C# 中的 MailboxProcessor 类型.一些困难是该类型使用了一些 F# 特定功能(可选参数是选项，函数是 FSharpFunc 类型等)

With a bit of pretty horrible hacking, you can use the MailboxProcessor type from C# using async. Some difficulties are that the type uses some F# specific features (optional arguments are options, functions are FSharpFunc type, etc.)

从技术上讲，最大的区别是 F# async 被处理，而 C# async 创建一个已经在运行的任务.这意味着要从 C# 构造 F# async，您需要编写一个接受 unt ->;任务 并创建Async.我写了一篇讨论差异的博客文章.

Technically, the biggest difference is that F# async is dealyed while C# async creates a task that is already running. This means that to construct F# async from C#, you need to write a method that takes unt -> Task<T> and creates Async<T>. I wrote a blog post that discusses the difference.

Anwyay，如果你想尝试，这里有一些代码你可以使用:

Anwyay, if you want to experiment, here is some code you can use:

static FSharpAsync<T> CreateAsync<T>(Func<Task<T>> f)
{ 
  return FSharpAsync.FromContinuations<T>(
    FuncConvert.ToFSharpFunc<
      Tuple< FSharpFunc<T, Unit>, 
             FSharpFunc<Exception, Unit>,
             FSharpFunc<OperationCanceledException, Unit> >>(conts => {
    f().ContinueWith(task => {
      try { conts.Item1.Invoke(task.Result); }
      catch (Exception e) { conts.Item2.Invoke(e); }
    });
  }));
}

static void MailboxProcessor() {
  var body = FuncConvert.ToFSharpFunc<
                FSharpMailboxProcessor<int>, 
                FSharpAsync<Unit>>(mbox =>
    CreateAsync<Unit>(async () => {
      while (true) {
        var msg = await FSharpAsync.StartAsTask
          ( mbox.Receive(FSharpOption<int>.None), 
            FSharpOption<TaskCreationOptions>.None, 
            FSharpOption<CancellationToken>.None );
        Console.WriteLine(msg);
      }
      return null;
    }));
  var agent = FSharpMailboxProcessor<int>.Start(body,
                FSharpOption<CancellationToken>.None);
  agent.Post(1);
  agent.Post(2);
  agent.Post(3);
  Console.ReadLine();
}

正如你所看到的，这看起来真的很可怕:-).

As you can see, this looks really horrible :-).

• 原则上，可以为 MailboxProcessor 类型编写一个 C# 友好的包装器(只需从这段代码中提取丑陋的部分)，但存在一些问题.

• In principle, it could be possible to write a C# friendly wrapper for the MailboxProcessor type (just extract the ugly bits from this code), but there are some problems.

在 F# 中，您经常使用尾递归异步来实现邮箱处理器中的状态机.如果你用 C# 写同样的东西，你最终会得到 StackOverflow，所以你需要编写具有可变状态的循环.

In F# you often use tail-recursive asyncs to implement the state machine in the mailbox processor. If you write the same thing in C#, you'll eventually get StackOverflow, so you'd need to write loops with mutable state.

完全可以用 F# 编写代理并从 C# 调用它.这只是从 F# 公开 C# 友好界面的问题(使用 Async.StartAsTask 方法).

It is perfectly possible to write the agent in F# and call it from C#. This is just a matter of exposing C#-friendly interface from F# (using the Async.StartAsTask method).

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