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

Like MailboxProcessor.PostAndReply, but returns None if there is no reply within the timeout period.

Namespace/Module Path: Microsoft.FSharp.Control

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

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

// Usage:
mailboxProcessor.TryPostAndReply (buildMessage)
mailboxProcessor.TryPostAndReply (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. Defaults to -1 which corresponds to Infinite.

The reply from the agent or None if the timeout expires.

The following example shows how to use TryPostAndReply. In this example, the agent has a delay that eventually results in a timeout.

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 will trigger a timeout. 
                do! Async.Sleep(200 * n );
                if (message = "Stop") then
                    replyChannel.Reply("Stop")
                else
                    replyChannel.Reply(String.Format(formatString, n, message))
                do! loop (n + 1)
        }
    loop 0)

let asyncReadInput =
   async {
       printf "> " 
       let input = Console.ReadLine();
       return input
   }

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

let rec loop() =
    Async.StartWithContinuations(asyncReadInput, (fun input ->
        let reply = agent.TryPostAndReply((fun replyChannel -> input, replyChannel), 1000)
        match reply with
        | None -> printfn "Timeout exceeded."
        | Some(reply) ->
            if (reply <> "Stop") then
                printfn "Reply: %s" reply
                loop()
            else
                ()),
        (fun exn -> ()),
        (fun _ -> ()))
loop()

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
Reply: Message number 0 was received. Message contents: test1
> test2
Reply: Message number 1 was received. Message contents: test2
> test3
Reply: Message number 2 was received. Message contents: test3
> test4
Reply: Message number 3 was received. Message contents: test4
> test5
Reply: Message number 4 was received. Message contents: test5
> test6
Timeout exceeded.
Press Enter to continue.

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

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