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F# Future using lazy and a threading event

F# Future using lazy and a threading event. Supports creating futures from functions or asyncs. Eager evaluation of can be specified.

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open System.Threading;

let lazyFuture (f : unit -> 'a) =
    let sub = new ReplaySubject<'a option * Exception>()
    async {
        try
            let r = f()
            sub.OnNext(Some r,null); ()
            ()
        with
        | ex -> sub.OnNext(None,ex); ()
        
    } |> Async.Start
    lazy
    (
        match sub.ToEnumerable().First() with
        | (Some r,_) -> r
        | (_,e) -> raise e
    )

let v = lazyFuture (fun () -> Thread.Sleep(3000); 10)

v.Force() |> printfn "%A"
namespace System
namespace System.Threading
val lazyFuture : f:(unit -> 'a) -> Lazy<'a0>

Full name: Script.lazyFuture
val f : (unit -> 'a)
type unit = Unit

Full name: Microsoft.FSharp.Core.unit
val sub : obj
type 'T option = Option<'T>

Full name: Microsoft.FSharp.Core.option<_>
val async : AsyncBuilder

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.async
val r : 'a
union case Option.Some: Value: 'T -> Option<'T>
val ex : exn
union case Option.None: Option<'T>
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<_>
static member Async.Start : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
val e : System.Exception
val raise : exn:System.Exception -> 'T

Full name: Microsoft.FSharp.Core.Operators.raise
val v : Lazy<obj>

Full name: Script.v
Multiple items
type Thread =
  inherit CriticalFinalizerObject
  new : start:ThreadStart -> Thread + 3 overloads
  member Abort : unit -> unit + 1 overload
  member ApartmentState : ApartmentState with get, set
  member CurrentCulture : CultureInfo with get, set
  member CurrentUICulture : CultureInfo with get, set
  member DisableComObjectEagerCleanup : unit -> unit
  member ExecutionContext : ExecutionContext
  member GetApartmentState : unit -> ApartmentState
  member GetCompressedStack : unit -> CompressedStack
  member GetHashCode : unit -> int
  ...

Full name: System.Threading.Thread

--------------------
Thread(start: ThreadStart) : unit
Thread(start: ParameterizedThreadStart) : unit
Thread(start: ThreadStart, maxStackSize: int) : unit
Thread(start: ParameterizedThreadStart, maxStackSize: int) : unit
Thread.Sleep(timeout: System.TimeSpan) : unit
Thread.Sleep(millisecondsTimeout: int) : unit
member System.Lazy.Force : unit -> 'T
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

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

More information

Link:http://fssnip.net/5V
Posted:8 years ago
Author:Ankur Dhama
Tags: lazy , threading , synchronization