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Creating observable using Async.StartDisposable

Implements a simple Async.StartDisposable extension that can be used to easily create IObservable values from F# asynchronous workflows. The method starts an asynchronous workflow and returns IDisposable that cancels the workflow when disposed.

StartDisposable extension

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open System

type Microsoft.FSharp.Control.Async with
  /// Starts the specified operation using a new CancellationToken and returns
  /// IDisposable object that cancels the computation. This method can be used
  /// when implementing the Subscribe method of IObservable interface.
  static member StartDisposable(op:Async<unit>) =
    let ct = new System.Threading.CancellationTokenSource()
    Async.Start(op, ct.Token)
    { new IDisposable with 
        member x.Dispose() = ct.Cancel() }

Creating counter observable

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/// Creates IObservable that fires numbers with specified delay
let createCounterEvent (delay) =

  /// Recursive async computation that triggers observer
  let rec counter (observer:IObserver<_>) count = async {
    do! Async.Sleep(delay)
    observer.OnNext(count)
    return! counter observer (count + 1) }

  // Return new IObservable that starts 'counter' using
  // 'StartDisposable' when a new client subscribes.
  { new IObservable<_> with
      member x.Subscribe(observer) =
        counter observer 0
        |> Async.StartDisposable }

// Start the counter with 1 second delay and print numbers
let disp = 
  createCounterEvent 1000
  |> Observable.map (sprintf "Count: %d")
  |> Observable.subscribe (printfn "%s")

// Dispose of the observer (and underlying async)
disp.Dispose()
namespace System
namespace Microsoft
namespace Microsoft.FSharp
namespace Microsoft.FSharp.Control
Multiple items
type Async<'T>

Full name: Microsoft.FSharp.Control.Async<_>

--------------------
type Async
static member AsBeginEnd : computation:('Arg -> Async<'T>) -> ('Arg * AsyncCallback * obj -> IAsyncResult) * (IAsyncResult -> 'T) * (IAsyncResult -> unit)
static member AwaitEvent : event:IEvent<'Del,'T> * ?cancelAction:(unit -> unit) -> Async<'T> (requires delegate and 'Del :> Delegate)
static member AwaitIAsyncResult : iar:IAsyncResult * ?millisecondsTimeout:int -> Async<bool>
static member AwaitTask : task:Task<'T> -> Async<'T>
static member AwaitWaitHandle : waitHandle:WaitHandle * ?millisecondsTimeout:int -> Async<bool>
static member CancelDefaultToken : unit -> unit
static member Catch : computation:Async<'T> -> Async<Choice<'T,exn>>
static member FromBeginEnd : beginAction:(AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg:'Arg1 * beginAction:('Arg1 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * beginAction:('Arg1 * 'Arg2 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * arg3:'Arg3 * beginAction:('Arg1 * 'Arg2 * 'Arg3 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromContinuations : callback:(('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) -> unit) -> Async<'T>
static member Ignore : computation:Async<'T> -> Async<unit>
static member OnCancel : interruption:(unit -> unit) -> Async<IDisposable>
static member Parallel : computations:seq<Async<'T>> -> Async<'T []>
static member RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:CancellationToken -> 'T
static member Sleep : millisecondsDueTime:int -> Async<unit>
static member Start : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions * ?cancellationToken:CancellationToken -> Task<'T>
static member StartChild : computation:Async<'T> * ?millisecondsTimeout:int -> Async<Async<'T>>
static member StartChildAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions -> Async<Task<'T>>
static member StartImmediate : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartWithContinuations : computation:Async<'T> * continuation:('T -> unit) * exceptionContinuation:(exn -> unit) * cancellationContinuation:(OperationCanceledException -> unit) * ?cancellationToken:CancellationToken -> unit
static member SwitchToContext : syncContext:SynchronizationContext -> Async<unit>
static member SwitchToNewThread : unit -> Async<unit>
static member SwitchToThreadPool : unit -> Async<unit>
static member TryCancelled : computation:Async<'T> * compensation:(OperationCanceledException -> unit) -> Async<'T>
static member CancellationToken : Async<CancellationToken>
static member DefaultCancellationToken : CancellationToken

Full name: Microsoft.FSharp.Control.Async
static member Async.StartDisposable : op:Async<unit> -> IDisposable

Full name: Script.StartDisposable


 Starts the specified operation using a new CancellationToken and returns
 IDisposable object that cancels the computation. This method can be used
 when implementing the Subscribe method of IObservable interface.
val op : Async<unit>
Multiple items
type Async
static member AsBeginEnd : computation:('Arg -> Async<'T>) -> ('Arg * AsyncCallback * obj -> IAsyncResult) * (IAsyncResult -> 'T) * (IAsyncResult -> unit)
static member AwaitEvent : event:IEvent<'Del,'T> * ?cancelAction:(unit -> unit) -> Async<'T> (requires delegate and 'Del :> Delegate)
static member AwaitIAsyncResult : iar:IAsyncResult * ?millisecondsTimeout:int -> Async<bool>
static member AwaitTask : task:Task<'T> -> Async<'T>
static member AwaitWaitHandle : waitHandle:WaitHandle * ?millisecondsTimeout:int -> Async<bool>
static member CancelDefaultToken : unit -> unit
static member Catch : computation:Async<'T> -> Async<Choice<'T,exn>>
static member FromBeginEnd : beginAction:(AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg:'Arg1 * beginAction:('Arg1 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * beginAction:('Arg1 * 'Arg2 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * arg3:'Arg3 * beginAction:('Arg1 * 'Arg2 * 'Arg3 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromContinuations : callback:(('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) -> unit) -> Async<'T>
static member Ignore : computation:Async<'T> -> Async<unit>
static member OnCancel : interruption:(unit -> unit) -> Async<IDisposable>
static member Parallel : computations:seq<Async<'T>> -> Async<'T []>
static member RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:CancellationToken -> 'T
static member Sleep : millisecondsDueTime:int -> Async<unit>
static member Start : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions * ?cancellationToken:CancellationToken -> Task<'T>
static member StartChild : computation:Async<'T> * ?millisecondsTimeout:int -> Async<Async<'T>>
static member StartChildAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions -> Async<Task<'T>>
static member StartImmediate : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartWithContinuations : computation:Async<'T> * continuation:('T -> unit) * exceptionContinuation:(exn -> unit) * cancellationContinuation:(OperationCanceledException -> unit) * ?cancellationToken:CancellationToken -> unit
static member SwitchToContext : syncContext:SynchronizationContext -> Async<unit>
static member SwitchToNewThread : unit -> Async<unit>
static member SwitchToThreadPool : unit -> Async<unit>
static member TryCancelled : computation:Async<'T> * compensation:(OperationCanceledException -> unit) -> Async<'T>
static member CancellationToken : Async<CancellationToken>
static member DefaultCancellationToken : CancellationToken

Full name: Microsoft.FSharp.Control.Async

--------------------
type Async<'T>

Full name: Microsoft.FSharp.Control.Async<_>
type unit = Unit

Full name: Microsoft.FSharp.Core.unit
val ct : Threading.CancellationTokenSource
namespace System.Threading
Multiple items
type CancellationTokenSource =
  new : unit -> CancellationTokenSource
  member Cancel : unit -> unit + 1 overload
  member Dispose : unit -> unit
  member IsCancellationRequested : bool
  member Token : CancellationToken
  static member CreateLinkedTokenSource : [<ParamArray>] tokens:CancellationToken[] -> CancellationTokenSource + 1 overload

Full name: System.Threading.CancellationTokenSource

--------------------
Threading.CancellationTokenSource() : unit
static member Async.Start : computation:Async<unit> * ?cancellationToken:Threading.CancellationToken -> unit
property Threading.CancellationTokenSource.Token: Threading.CancellationToken
type IDisposable =
  member Dispose : unit -> unit

Full name: System.IDisposable
val x : IDisposable
IDisposable.Dispose() : unit
Threading.CancellationTokenSource.Cancel() : unit
Threading.CancellationTokenSource.Cancel(throwOnFirstException: bool) : unit
val createCounterEvent : delay:int -> IObservable<int>

Full name: Script.createCounterEvent


 Creates IObservable that fires numbers with specified delay
val delay : int
val counter : (IObserver<int> -> int -> Async<'a>)


 Recursive async computation that triggers observer
val observer : IObserver<int>
type IObserver<'T> =
  member OnCompleted : unit -> unit
  member OnError : error:Exception -> unit
  member OnNext : value:'T -> unit

Full name: System.IObserver<_>
val count : int
val async : AsyncBuilder

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.async
static member Async.Sleep : millisecondsDueTime:int -> Async<unit>
IObserver.OnNext(value: int) : unit
type IObservable<'T> =
  member Subscribe : observer:IObserver<'T> -> IDisposable

Full name: System.IObservable<_>
val x : IObservable<int>
member IObservable.Subscribe : callback:('T -> unit) -> IDisposable
IObservable.Subscribe(observer: IObserver<int>) : IDisposable
static member Async.StartDisposable : op:Async<unit> -> IDisposable


 Starts the specified operation using a new CancellationToken and returns
 IDisposable object that cancels the computation. This method can be used
 when implementing the Subscribe method of IObservable interface.
val disp : IDisposable

Full name: Script.disp
module Observable

from Microsoft.FSharp.Control
val map : mapping:('T -> 'U) -> source:IObservable<'T> -> IObservable<'U>

Full name: Microsoft.FSharp.Control.Observable.map
val sprintf : format:Printf.StringFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.sprintf
val subscribe : callback:('T -> unit) -> source:IObservable<'T> -> IDisposable

Full name: Microsoft.FSharp.Control.Observable.subscribe
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

More information

Link:http://fssnip.net/7Y
Posted:13 years ago
Author:Tomas Petricek
Tags: async , asynchronous workflows , observable , event , dispose

This web site is created using F# and Suave web server. It is hosted on Azure and the source code is on GitHub. Contributions are welcome!

The first version of fssnip.net has been created by @tomaspetricek back in 2010. This web site is a new, open-source and contribution-friendly version.