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

Creates an asynchronous computation in terms of a Begin/End pair of actions in the style used in CLI APIs.

Namespace/Module Path: Microsoft.FSharp.Control

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

// Signature:
static member FromBeginEnd : (AsyncCallback * obj -> IAsyncResult) * (IAsyncResult -> 'T) * ?(unit -> unit) -> Async<'T>

// Usage:
Async.FromBeginEnd (beginAction, endAction)
Async.FromBeginEnd (beginAction, endAction, cancelAction = cancelAction)

Parameters

  • beginAction
    Type: AsyncCallback * obj -> IAsyncResult

    The function initiating a traditional CLI asynchronous operation.

  • endAction
    Type: IAsyncResult -> 'T

    The function completing a traditional CLI asynchronous operation.

  • cancelAction
    Type: (unit -> unit)

    An optional function to be executed when a cancellation is requested.

Return Value

An asynchronous computation wrapping the given Begin/End functions.

Remarks

For example, the following code creates an asynchronous computation that wraps a web service call.

Async.FromBeginEnd(ws.BeginGetWeather,ws.EndGetWeather)

When the computation is run, beginFunc is executed, with a callback which represents the continuation of the computation. When the callback is invoked, the overall result is fetched using endFunc.

The computation will respond to cancellation while waiting for the completion of the operation. If a cancellation occurs, and cancelAction is specified, then it is executed, and the computation continues to wait for the completion of the operation. If cancelAction is not specified, cancellation causes the computation to stop immediately, and subsequent invocations of the callback are ignored.

Example

The following code example shows how to create an F# asynchronous computation from a .NET asynchronous API that uses the Begin/End pattern. The example uses the .NET socket API in System.Net.Sockets. It is an implementation of a simple server application that accepts a connection, receives data from a client, and sends a response.

module SocketServer =

    open System.Net
    open System.Net.Sockets
    open System.Collections.Generic

    let toIList<'T> (data : 'T array) =
        let segment = new System.ArraySegment<'T>(data)
        let data = new List<System.ArraySegment<'T>>() :> IList<System.ArraySegment<'T>>
        data.Add(segment)
        data

    type Socket with 
        member this.MyAcceptAsync() =
            Async.FromBeginEnd((fun (callback, state) -> this.BeginAccept(callback, state)),
                               this.EndAccept)
        member this.MyConnectAsync(ipAddress : IPAddress, port : int) =
            Async.FromBeginEnd(ipAddress, port,
                               (fun (ipAddress:IPAddress, port, callback, state) ->
                                   this.BeginConnect(ipAddress, port, callback, state)),
                               this.EndConnect)
        member this.MySendAsync(data : byte array, flags : SocketFlags) =
            Async.FromBeginEnd(toIList data, flags, 
                               (fun (data : IList<System.ArraySegment<byte>>,
                                     flags : SocketFlags, callback, state) ->
                                         this.BeginSend(data, flags, callback, state)),
                               this.EndSend)
        member this.MyReceiveAsync(data : byte array, flags : SocketFlags) =
            Async.FromBeginEnd(toIList data, flags, 
                               (fun (data : IList<System.ArraySegment<byte>>,
                                     flags : SocketFlags, callback, state) ->
                                         this.BeginReceive(data, flags, callback, state)),
                               this.EndReceive)

    let port = 11000

    let socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
    let ipHostInfo = Dns.Resolve(Dns.GetHostName())
    let localIPAddress = ipHostInfo.AddressList.[0]
    let localEndPoint = new IPEndPoint(localIPAddress, port)
    socket.Bind(localEndPoint)


    let connectSendReceive (socket : Socket) =
        async {
            do! socket.MyConnectAsync(ipHostInfo.AddressList.[0], 11000)
            let buffer1 = [| 0uy .. 255uy |]
            let buffer2 = Array.zeroCreate<byte> 255
            let flags = new SocketFlags()
            let! flag = socket.MySendAsync(buffer1, flags)
            let! result = socket.MyReceiveAsync(buffer2, flags)
            return buffer2
        }

    let acceptReceiveSend (socket : Socket) =
        async {
            printfn "Listening..."
            socket.Listen(10)
            printfn "Accepting..." 
            let! socket = socket.MyAcceptAsync()

            let buffer1 = Array.zeroCreate<byte> 256
            let flags = new SocketFlags()
            printfn "Receiving..." 
            let! nBytes = socket.MyReceiveAsync(buffer1, flags)
            printfn "Received %d bytes from client computer." nBytes
            let buffer2 = Array.rev buffer1
            printfn "Sending..." 
            let! flag = socket.MySendAsync(buffer2, flags)
            printfn "Completed." 
            return buffer2
        }

    let taskServer = Async.StartAsTask(acceptReceiveSend(socket))    
    taskServer.Wait()
    socket.Close()

Output

Listening...

Accepting...

Receiving...

Received 256 bytes from client computer.

Sending...

Completed.

The following code example shows the client code that can be used together with the server code in the previous example.

module SocketClient =

    open System.Net
    open System.Net.Sockets
    open System.Collections.Generic

    let toIList<'T> (data : 'T array) =
        let segment = new System.ArraySegment<'T>(data)
        let data = new List<System.ArraySegment<'T>>() :> IList<System.ArraySegment<'T>>
        data.Add(segment)
        data

    type Socket with 
        member this.MyAcceptAsync(receiveSize) =
            Async.FromBeginEnd(receiveSize,
                               (fun (receiveSize, callback, state) ->
                                   this.BeginAccept(receiveSize, callback, state)),
                               this.EndConnect)
        member this.MyConnectAsync(ipAddress : IPAddress, port : int) =
            Async.FromBeginEnd(ipAddress, port,
                               (fun (ipAddress:IPAddress, port, callback, state) ->
                                   this.BeginConnect(ipAddress, port, callback, state)),
                               this.EndConnect)
        member this.MySendAsync(data, flags : SocketFlags) =
            Async.FromBeginEnd(toIList data, flags, 
                               (fun (data : IList<System.ArraySegment<byte>>,
                                     flags : SocketFlags, callback, state) ->
                                         this.BeginSend(data, flags, callback, state)),
                               this.EndSend)
        member this.MyReceiveAsync(data, flags : SocketFlags) =
            Async.FromBeginEnd(toIList data, flags, 
                               (fun (data : IList<System.ArraySegment<byte>>,
                                     flags : SocketFlags, callback, state) ->
                                         this.BeginReceive(data, flags, callback, state)),
                               this.EndReceive)

    let port = 11000

    let socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
    let ipHostEntry = Dns.Resolve("hostname.contoso.com")
    printfn "Server address: %s" (ipHostEntry.AddressList.[0].ToString())

    let connectSendReceive (socket : Socket) =
        async {
            do! socket.MyConnectAsync(ipHostEntry.AddressList.[0], 11000)
            printfn "Connected to remote host." 
            let buffer1 = [| 0uy .. 255uy |]
            let buffer2 = Array.zeroCreate<byte> 255
            let flags = new SocketFlags()
            printfn "Sending data..." 
            let! flag = socket.MySendAsync(buffer1, flags)
            printfn "Receiving data..." 
            let! result = socket.MyReceiveAsync(buffer2, flags)
            printfn "Received data from remote host." 
            return buffer2
        }

    let acceptReceiveSend (socket : Socket) =
        async {
            socket.Listen(1)
            do! socket.MyAcceptAsync(256)
            let buffer1 = Array.zeroCreate<byte> 255
            let flags = new SocketFlags()
            let! flag = socket.MyReceiveAsync(buffer1, flags)
            let buffer2 = Array.rev buffer1
            let! flag = socket.MySendAsync(buffer2, flags)
            return buffer2
        }

    let taskClient = Async.StartAsTask(connectSendReceive(socket))

    taskClient.Wait()
    taskClient.Result |> Array.iter (fun elem -> printf "%d " elem)

Sample Output

Server address: 10.80.57.8

Connected to remote host.

Sending data...

Receiving data...

Received data from remote host.

255 254 253 252 251 250 249 248 247 246 ...

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

See Also

Reference

Control.Async Class (F#)

Microsoft.FSharp.Control Namespace (F#)