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GuardedAwaitObservable.fs
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GuardedAwaitObservable.fs
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module internal Fake.Core.GuardedAwaitObservable
// from https://github.com/fsprojects/fsharpx/blob/f99a8f669ab49166c854c479d17c3add2b39f8d7/src/FSharpx.Core/Observable.fs
// TODO: reference FSharpx.Async once it supports netstandard...
open System
open System.Threading
/// <summary>
/// Helper that can be used for writing CPS-style code that resumes
/// on the same thread where the operation was started.
/// </summary>
let private synchronize f =
let ctx = SynchronizationContext.Current
f (fun g ->
let nctx = SynchronizationContext.Current
if not (isNull ctx) && ctx <> nctx then
ctx.Post((fun _ -> g ()), null)
else
g ())
type Microsoft.FSharp.Control.Async with
/// Behaves like AwaitObservable, but calls the specified guarding function
/// after a subscriber is registered with the observable.
static member GuardedAwaitObservable (ev1: IObservable<'T1>) guardFunction =
let removeObj: IDisposable option ref = ref None
let removeLock = obj ()
let setRemover r =
lock removeLock (fun () -> removeObj.Value <- Some r)
let remove () =
lock removeLock (fun () ->
match removeObj.Value with
| Some d ->
removeObj.Value <- None
d.Dispose()
| None -> ())
synchronize (fun f ->
let workflow =
Async.FromContinuations(fun (cont, econt, ccont) ->
let rec finish cont value =
remove ()
f (fun () -> cont value)
setRemover
<| ev1.Subscribe(
{ new IObserver<_> with
member _.OnNext(v) = finish cont v
member _.OnError(e) = finish econt e
member _.OnCompleted() =
let msg =
"Cancelling the workflow, because the Observable awaited using AwaitObservable has completed."
finish ccont (OperationCanceledException(msg)) }
)
guardFunction ())
async {
let! cToken = Async.CancellationToken
let token: CancellationToken = cToken
use registration = token.Register(fun () -> remove ())
return! workflow
})