MailboxProcessor.Start<'Msg> Method (F#)
Creates and starts an agent.
Namespace/Module Path: Microsoft.FSharp.Control
Assembly: FSharp.Core (in FSharp.Core.dll)
// Signature:
static member Start : (MailboxProcessor<'Msg> -> Async<unit>) * ?CancellationToken -> MailboxProcessor<'Msg>
// Usage:
MailboxProcessor.Start (body)
MailboxProcessor.Start (body, cancellationToken = cancellationToken)
Parameters
body
Type: MailboxProcessor<'Msg> -> Async<unit>The function to produce an asynchronous computation that will be executed as the read loop for the MailboxProcessor when Start is called.
cancellationToken
Type: CancellationTokenAn optional cancellation token for the body. The default is Async.DefaultCancellationToken.
Return Value
The created MailboxProcessor.
Remarks
The body function is used to generate the asynchronous computation executed by the agent.
Example
The following code example shows how to start a mailbox processor agent. In this example, each line of input from the console is posted to a message queue. The program reads each message and replies by using a reply channel. When the special message "Stop" is received, the Stop reply is sent and the program exits.
open System
type Message = string * AsyncReplyChannel<string>
let formatString = "Message number {0} was received. Message contents: {1}"
let printThreadId note =
// Append the thread ID.
printfn "%d : %s" System.Threading.Thread.CurrentThread.ManagedThreadId note
let agent = MailboxProcessor<Message>.Start(fun inbox ->
let rec loop n =
async {
let! (message, replyChannel) = inbox.Receive();
printThreadId "MailboxProcessor"
if (message = "Stop") then
replyChannel.Reply("Stopping.")
else
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 rec loop() =
printf "> "
let input = Console.ReadLine()
printThreadId("Console loop")
let reply = agent.PostAndReply(fun replyChannel -> input, replyChannel)
if (reply <> "Stopping.") then
printfn "Reply: %s" reply
loop()
else
()
loop()
printfn "Press Enter to continue."
Console.ReadLine() |> ignore
Following is an example session.
Mailbox Processor Test Type some text and press Enter to submit a message. Type 'Stop' to close the program. > hello 1 : Console loop 4 : mailboxProcessor Reply: Message number 0 was received. Message contents: hello > testing 1 : Console loop 3 : mailboxProcessor Reply: Message number 1 was received. Message contents: testing > hello? 1 : Console loop 4 : mailboxProcessor Reply: Message number 2 was received. Message contents: hello? > testing 1 2 3 1 : Console loop 3 : mailboxProcessor Reply: Message number 3 was received. Message contents: testing 1 2 3 > Stop 1 : Console loop 4 : mailboxProcessor Press Enter to continue.
Platforms
Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2
Version Information
F# Core Library Versions
Supported in: 2.0, 4.0, Portable