异步等待 n 件事发生

Question

我正在寻找类似 Semaphore 的东西，但在释放所有插槽后解决。

像这样：

use semaphore = new SemaphoreSlim(0,100)

anEvent.add(fun _ -> semaphore.Release(1) |> ignore);

async {
   do! thingThatCausesAnEventToFire100Times()
   //where 100 is the available slots instead of the timeout.
   let! thingsHappened = semaphore.WaitAsync(100) |> Async.AwaitTask
   thingsHappened |> should be True
}

Answer 1

听起来像是 MailboxProcessor 的工作。这个怎么样：

type SemaphoreCommand =
  |Release
  |Wait of AsyncReplyChannel<unit>

let semaphore slots =
    Agent.Start
    <| fun inbox ->
        let rec loop c (w:AsyncReplyChannel<unit> list) =
          async {
            let! command = inbox.Receive()
            match command with
            |Release -> if (c + 1) = slots then w |> List.iter(fun t -> t.Reply()) 
                        else return! loop (c + 1) w
            |Wait a -> return! loop c (a::w)
        }
        loop 0 []

let slotWaiter = semaphore 100

//Events will fill up slots
Release |> slotWaiter.Post
Release |> slotWaiter.Post

async{
  //Wait for all slots to be filled
  do! slotWaiter.PostAndAsyncReply(fun t -> Wait t)
  //All slots filled - continue
}

我不会处理这样的情况，即您可能在所有槽都填满时尚未注册 AsyncReplyChannel，或者在所有槽都填满后重置，但这是相当微不足道的，我将把它留作练习reader :)

异步等待 n 件事发生

Asynchronously wait for n things to happen

.net

f#

asynchronous

semaphore