gistfile1.fs

type Message = 
    | Sleep of int*int
    | SyncPoint of AsyncReplyChannel<unit>

let agent =
    MailboxProcessor.Start(fun inbox ->
        let rec loop() =
            async { 
                    let! msg = inbox.Receive()
                    match msg with
                    | Sleep(i,time) ->
                        printfn "%d - sleeping %d" i time 
                        System.Threading.Thread.Sleep(time)
                    | SyncPoint(replyChannel) ->
                        replyChannel.Reply()
                    return! loop()}
        loop())

//Task generator
let rnd = new System.Random(100)
for x in 1..20 do
    agent.Post (Sleep(x,rnd.Next(1000)))

//Sync Point
let messageAsync = agent.PostAndAsyncReply(fun replyChannel -> SyncPoint(replyChannel))
Async.RunSynchronously(messageAsync)
printfn "FINISH"