Async.Start Method (F#)

Starts the asynchronous computation in the thread pool. Do not await its result.

Namespace/Module Path: Microsoft.FSharp.Control

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

// Signature:
static member Start : Async<unit> * ?CancellationToken -> unit

// Usage:
Async.Start (computation)
Async.Start (computation, cancellationToken = cancellationToken)


  • computation
    Type: Async<unit>

    The computation to run asynchronously.

  • cancellationToken
    Type: CancellationToken

    The cancellation token to be associated with the computation. If one is not supplied, the default cancellation token is used.


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


The following code example shows how to start an asynchronous computation on the thread pool.

open System.Windows.Forms

let bufferData = Array.zeroCreate<byte> 100000000

let async1 =
     async {
       use outputFile = System.IO.File.Create("longoutput.dat")
       do! outputFile.AsyncWrite(bufferData) 

let form = new Form(Text = "Test Form")
let button = new Button(Text = "Start")
button.Click.Add(fun args -> Async.Start(async1))


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

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also


Control.Async Class (F#)

Microsoft.FSharp.Control Namespace (F#)