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MailboxProcessor.PostAndTryAsyncReply<'Msg,'Reply> Method (F#)

Den Delimarsky|Last Updated: 8/18/2017
1 Contributor

Like MailboxProcessor.AsyncPostAndReply, but returns None if no reply within the timeout period.

Namespace/Module Path: Microsoft.FSharp.Control

Assembly: FSharp.Core (in FSharp.Core.dll)


// Signature:
member this.PostAndTryAsyncReply : (AsyncReplyChannel<'Reply> -> 'Msg) * ?int -> Async<'Reply option>

// Usage:
mailboxProcessor.PostAndTryAsyncReply (buildMessage)
mailboxProcessor.PostAndTryAsyncReply (buildMessage, timeout = timeout)


buildMessage Type: AsyncReplyChannel<'Reply> -> 'Msg

The function to incorporate the AsyncReplyChannel into the message to be sent.

timeout Type: int

An optional timeout parameter (in milliseconds) to wait for a reply message. The default is -1 which corresponds to System.Threading.Timeout.Infinite.

Return Value

An asynchronous computation (Async object) that will return the reply or None if the timeout expires.


open System

type Message = string * AsyncReplyChannel<string>

let formatString = "Message number {0} was received. Message contents: {1}"

let agent = MailboxProcessor<Message>.Start(fun inbox ->
    let rec loop n =
        async {          
            let! (message, replyChannel) = inbox.Receive();
            // The delay gets longer with each message, and eventually triggers a timeout.
            do! Async.Sleep(200 * n );
            if (message = "Stop") then
                replyChannel.Reply(String.Format(formatString, n, message))
            do! loop (n + 1)
    loop (0))

printfn "Mailbox Processor Test"
printfn "Type some text and press Enter to submit a message."
printfn "Type 'Stop' to close the program."

let mutable isCompleted = false
while (not isCompleted) do
    printf "> "
    let input = Console.ReadLine()
    let messageAsync = agent.PostAndTryAsyncReply((fun replyChannel -> input, replyChannel), 1000)
    // Set up a continuation function (the first argument below) that prints the reply.
    // The second argument is the exception continuation.
    // The third argument is the cancellation continuation (not used).
         (fun reply -> 
             match reply with
             | None -> printfn "Reply timeout exceeded."
             | Some reply -> if (reply = "Stop") then
                                 isCompleted <- true
                             else printfn "%s" reply),
         (fun exn ->
            printfn "Exception occurred: %s" exn.Message),
         (fun _ -> ()))

printfn "Press Enter to continue."
Console.ReadLine() |> ignore

A sample session follows.

Mailbox Processor Test
Type some text and press Enter to submit a message.
Type 'Stop' to close the program.
> test1
> Message number 0 was received. Message contents: test1
> Message number 1 was received. Message contents: test2
> Message number 2 was received. Message contents: test3
> Message number 3 was received. Message contents: test4
> Message number 4 was received. Message contents: test5
> Reply timeout exceeded.

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also

Control.MailboxProcessor<'Msg> Class (F#)

Microsoft.FSharp.Control Namespace (F#)

© 2020 Microsoft