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Await completed Tasks on the same thread. #11142

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Merged
cartermp merged 4 commits into from
Feb 25, 2021
Merged

Await completed Tasks on the same thread. #11142

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9becffa
Run the continations synchronously in AsyncPrimitives.taskContinueWith.
teo-tsirpanis Nov 17, 2020
a64258e
Use Thread.IsThreadPoolThread in AsyncPrimitives.RunSynchronously.
teo-tsirpanis Feb 25, 2021
02c7f04
Do not preserve the synchronization context when awaiting a completed…
teo-tsirpanis Feb 24, 2021
f753263
Add a unit test that awaits a completed task.
teo-tsirpanis Feb 24, 2021
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30 changes: 21 additions & 9 deletions src/fsharp/FSharp.Core/async.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -871,11 +871,9 @@ namespace Microsoft.FSharp.Control

[<DebuggerHidden>]
let RunSynchronously cancellationToken (computation: Async<'T>) timeout =
// Reuse the current ThreadPool thread if possible. Unfortunately
// Thread.IsThreadPoolThread isn't available on all profiles so
// we approximate it by testing synchronization context for null.
match SynchronizationContext.Current, timeout with
| null, None -> RunSynchronouslyInCurrentThread (cancellationToken, computation)
// Reuse the current ThreadPool thread if possible.
match Thread.CurrentThread.IsThreadPoolThread, timeout with
| true, None -> RunSynchronouslyInCurrentThread (cancellationToken, computation)
// When the timeout is given we need a dedicated thread
// which cancels the computation.
// Performing the cancellation in the ThreadPool eg. by using
Expand Down Expand Up @@ -941,7 +939,11 @@ namespace Microsoft.FSharp.Control
else
ctxt.cont completedTask.Result) |> unfake

task.ContinueWith(Action<Task<'T>>(continuation)) |> ignore |> fake
if task.IsCompleted then
continuation task |> fake
else
task.ContinueWith(Action<Task<'T>>(continuation), TaskContinuationOptions.ExecuteSynchronously)
|> ignore |> fake

[<DebuggerHidden>]
let taskContinueWithUnit (task: Task) (ctxt: AsyncActivation<unit>) useCcontForTaskCancellation =
Expand All @@ -960,7 +962,11 @@ namespace Microsoft.FSharp.Control
else
ctxt.cont ()) |> unfake

task.ContinueWith(Action<Task>(continuation)) |> ignore |> fake
if task.IsCompleted then
continuation task |> fake
else
task.ContinueWith(Action<Task>(continuation), TaskContinuationOptions.ExecuteSynchronously)
|> ignore |> fake

[<Sealed; AutoSerializable(false)>]
type AsyncIAsyncResult<'T>(callback: System.AsyncCallback, state:obj) =
Expand Down Expand Up @@ -1692,10 +1698,16 @@ namespace Microsoft.FSharp.Control
CreateWhenCancelledAsync compensation computation

static member AwaitTask (task:Task<'T>) : Async<'T> =
CreateDelimitedUserCodeAsync (fun ctxt -> taskContinueWith task ctxt false)
if task.IsCompleted then
CreateProtectedAsync (fun ctxt -> taskContinueWith task ctxt false)
else
CreateDelimitedUserCodeAsync (fun ctxt -> taskContinueWith task ctxt false)

static member AwaitTask (task:Task) : Async<unit> =
CreateDelimitedUserCodeAsync (fun ctxt -> taskContinueWithUnit task ctxt false)
if task.IsCompleted then
CreateProtectedAsync (fun ctxt -> taskContinueWithUnit task ctxt false)
else
CreateDelimitedUserCodeAsync (fun ctxt -> taskContinueWithUnit task ctxt false)

module CommonExtensions =

Expand Down
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