[英]No output in asynchronous functions using F#?
嘗試使用Blocking Queue和此處給出的代碼來實現讀寫器問題。 整個過程都已編譯並運行,但是reader()和writer()函數中async {...}中的部分均未產生任何輸出。 我敢肯定他們會被正確調用,因為即使我是F#的菜鳥,帶有此代碼的教程頁面似乎也是真實的。
這是整個代碼:
open System
open System.IO
open System.Collections.Generic
//open System.Runtime.Serialization.Formatters.Binary
///defining Agent
type Agent<'T> = MailboxProcessor<'T>
///defining Message
type internal BlockingAgentMessage<'T> =
| Get of AsyncReplyChannel<'T>
| Add of 'T * AsyncReplyChannel<unit>
/// Agent-based implementation of producer/consumer problem
type BlockingQueueAgent<'T>(maxLength) =
let agent = Agent.Start(fun agent ->
let queue = new Queue<_>()
//let queue = new Queue()
// State machine running inside the agent
let rec emptyQueue() =
agent.Scan(fun msg ->
match msg with
| Add(value, reply) -> Some(enqueueAndContinue(value, reply))
| _ -> None )
and fullQueue() =
agent.Scan(fun msg ->
match msg with
| Get(reply) -> Some(dequeueAndContinue(reply))
| _ -> None )
and runningQueue() = async {
let! msg = agent.Receive()
match msg with
| Add(value, reply) -> return! enqueueAndContinue(value, reply)
| Get(reply) -> return! dequeueAndContinue(reply) }
and enqueueAndContinue (value, reply) = async {
queue.Enqueue(value)
reply.Reply()
return! chooseState() }
and dequeueAndContinue (reply) = async {
reply.Reply(queue.Dequeue())
return! chooseState() }
and chooseState() =
if queue.Count = 0 then emptyQueue()
elif queue.Count = maxLength then fullQueue()
else runningQueue()
// Start with an empty queue
emptyQueue() )
/// Asynchronously adds item to the queue. If the queue
/// is full, it blocks until some items are removed.
member x.AsyncAdd(v:'T) =
agent.PostAndAsyncReply(fun ch -> Add(v, ch))
/// Asynchronously gets item from the queue. If the queue
/// is empty, it blocks until some items are added.
member x.AsyncGet() =
agent.PostAndAsyncReply(Get)
let ag = new BlockingQueueAgent<int>(3)
printfn "Blocking Queue Agent program"
let writer() = async {
for i in 0 .. 10 do
do! ag.AsyncAdd(i)
printfn "Added: %d" i }
let reader () = async {
while true do
let! v = ag.AsyncGet()
do! Async.Sleep(1000)
printfn "Got: %d" v }
reader () |> Async.Start
printfn "Started Reader ..."
writer () |> Async.Start
printfn "Started Writer ..."
代碼很好- async
執行之前,您的程序剛剛退出。 只需添加類似
System.Console.Read() |> ignore
到最后。 這對我有用
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