Async.StartWithContinuations<'T> Method (F#)

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Visual Studio 2010 - Visual F#

Updated: July 2010

Runs an asynchronous computation, starting immediately on the current operating system thread. Call one of the three continuations when the operation completes.

Namespace/Module Path: Microsoft.FSharp.Control

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

// Signature:
static member StartWithContinuations : Async<'T> * ('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) * ?CancellationToken -> unit

// Usage:
Async.StartWithContinuations (computation, continuation, exceptionContinuation, cancellationContinuation)
Async.StartWithContinuations (computation, continuation, exceptionContinuation, cancellationContinuation, cancellationToken = cancellationToken)

Parameters

computation

Type: Async<'T>

The asynchronous computation to execute.

continuation

Type: 'T -> unit

The function called on success.

exceptionContinuation

Type: exn -> unit

The function called on exception.

cancellationContinuation

Type: OperationCanceledException -> unit

The function called on cancellation.

cancellationToken

Type: CancellationToken

The optional cancellation token to associate with the computation. The default is used if this parameter is not provided.

Remarks

If no cancellation token is provided, the default cancellation token is used.

Example

The following code example illustrates the use of Async.StartWithContinuations.


open System.Windows.Forms

let bufferData = Array.zeroCreate<byte> 100000000

let async1 (label:System.Windows.Forms.Label) filename =
     Async.StartWithContinuations(
         async {
            label.Text <- "Operation started."
            use outputFile = System.IO.File.Create(filename)
            do! outputFile.AsyncWrite(bufferData)
            },
         (fun _ -> label.Text <- "Operation completed."),
         (fun _ -> label.Text <- "Operation failed."),
         (fun _ -> label.Text <- "Operation canceled."))



let form = new Form(Text = "Test Form")
let button1 = new Button(Text = "Start")
let button2 = new Button(Text = "Start Invalid", Top = button1.Height + 10)
let button3 = new Button(Text = "Cancel", Top = 2 * button1.Height + 20)
let label1 = new Label(Text = "", Width = 200, Top = 3 * button1.Height + 30)
form.Controls.AddRange [| button1; button2; button3; label1 |]
button1.Click.Add(fun args -> async1 label1 "longoutput.dat")
// Try an invalid filename to test the error case.
button2.Click.Add(fun args -> async1 label1 "|invalid.dat")
button3.Click.Add(fun args -> Async.CancelDefaultToken())
Application.Run(form)

Platforms

Windows 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2

Version Information

F# Runtime

Supported in: 2.0, 4.0

Silverlight

Supported in: 3

Reference

Control.Async Class (F#)

Microsoft.FSharp.Control Namespace (F#)

Change History

Date	History	Reason
July 2010	Added code example.	Information enhancement.

Date

History

Reason

July 2010

Added code example.

Information enhancement.