async_seq_bench_opt.fs

let par (degree: int) (f: 'a -> Async<'b>) : 'a -> Async<'b> =
    let agent = MailboxProcessor.Start <| fun mailbox -> 
        async {        
            use semaphore = new SemaphoreSlim(degree)
            let rec loop () = 
                async {
                    let! (x: 'a, rep: AsyncReplyChannel<'b>) = mailbox.Receive()
                    do! semaphore.WaitAsync() |> Async.AwaitTask
                    async {
                        try
                            let! r = f x
                            rep.Reply r
                        finally
                            semaphore.Release() |> ignore
                    } |> Async.Start
                    return! loop () 
                }
            return! loop () 
        }
    fun x -> agent.PostAndAsyncReply(fun repCh -> x, repCh)

let searchWithAsyncSeq (file: string) =
    use reader = new StreamReader(file)
    AsyncSeq.unfoldAsync (fun _ -> 
        async {
            let! line = reader.ReadLineAsync() |> Async.AwaitTask
            return Some (line, ())
        }) ()
    |> AsyncSeq.take 1000000
    |> AsyncSeq.chooseAsync (par 4 (fun line ->
         async {
            match regex.Match line with
            | m when m.Success -> return Some m.Groups.["name"].Value
            | _ -> return None
         }))
    |> AsyncSeq.mapAsync (par 4 (fun (name: string) -> async { return normalizeName name }))
    |> AsyncSeq.length
    |> Async.RunSynchronously

// Real: 00:00:29.538, CPU: 00:01:35.843, GC gen0: 5265, gen1: 7, gen2: 0
// val it : int64 = 24540L