[英]Use a MailboxProcessor with reply-channel to create limited agents that return values in order
基本上,我想將以下內容更改為有限的線程解決方案,因為在我的情況下,計算列表太大,產生了太多的線程,並且我想用更少的線程進行實驗和衡量性能。
// the trivial approach (and largely my current situation)
let doWork() =
[1 .. 10]
|> List.map (fun i -> async {
do! Async.Sleep (100 * i) // longest thread will run 1 sec
return i * i // some complex calculation returning a certain type
})
|> Async.Parallel
|> Async.RunSynchronously // works, total wall time 1s
我的新方法是從Tomas Petricek的此在線代碼段借用/啟發該代碼 (經過測試,它可以工作,但我需要它返回一個值,而不是單位)。
type LimitAgentMessage =
| Start of Async<int> * AsyncReplyChannel<int>
| Finished
let threadingLimitAgent limit = MailboxProcessor.Start(fun inbox -> async {
let queue = System.Collections.Generic.Queue<_>()
let count = ref 0
while true do
let! msg = inbox.Receive()
match msg with
| Start (work, reply) -> queue.Enqueue((work, reply))
| Finished -> decr count
if count.Value < limit && queue.Count > 0 then
incr count
let work, reply = queue.Dequeue()
// Start it in a thread pool (on background)
Async.Start(async {
let! x = work
do! async {reply.Reply x }
inbox.Post(Finished)
})
})
// given a synchronous list of tasks, run each task asynchronously,
// return calculated values in original order
let worker lst =
// this doesn't work as expected, it waits for each reply
let agent = threadingLimitAgent 10
lst
|> List.map(fun x ->
agent.PostAndReply(
fun replyChannel -> Start(x, replyChannel)))
現在,有了這個,原始代碼將變為:
let doWork() =
[1 .. 10]
|> List.map (fun i -> async {
do! Async.Sleep (100 * i) // longest thread will run 1 sec
return i * i // some complex calculation returning a certain type
})
|> worker // worker is not working (correct output, runs 5.5s)
總而言之,輸出是正確的(它確實計算並傳播了答復),但在(有限組)線程中卻不是這樣。
我一直在玩耍,但是我想我沒有找到明顯的東西(此外,有人知道,有人可能喜歡有限線程郵箱處理器的想法,該處理器按順序返回其計算結果)。
問題是對agent.PostAndReply
的調用。 PostAndReply
將阻塞,直到工作完成。 在List.map
調用此List.map
將導致工作按順序執行。 一種解決方案是使用PostAndAsyncReply
,它不會阻塞並且還會返回一個異步句柄以獲取結果。
let worker lst =
let agent = threadingLimitAgent 10
lst
|> List.map(fun x ->
agent.PostAndAsyncReply(
fun replyChannel -> Start(x, replyChannel)))
|> Async.Parallel
let doWork() =
[1 .. 10]
|> List.map (fun i -> async {
do! Async.Sleep (100 * i)
return i * i
})
|> worker
|> Async.RunSynchronously
當然,那只是一種可能的解決方案(獲取所有異步句柄並並行等待它們)。
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