BufferByCountAndTime impact to Async.StartWithContinuations

[vaspas]

Description

Async.StartWithContinuations call is blocked when using AsyncSeq.BufferByCountAndTime in async operation.

Repro steps

let op =
asyncSeq{
while true do
do! Async.Sleep 1000
yield 0
}
|> AsyncSeq.bufferByCountAndTime 10 1000
|> AsyncSeq.iter (printf "%A ")

let cts = new System.Threading.CancellationTokenSource()
Async.StartWithContinuations(op, ignore, ignore, ignore, cts.Token)

Expected behavior

Async.StartWithContinuations call is returned

Actual behavior

Async.StartWithContinuations call blocks thread.

Known workarounds

Related information

• Windows 10
• FSharp.Control.AsyncSeq (2.0.11)

[eulerfx]

Hi thanks for reporting, I'll take a look. I think it's the blocking call to Task.Wait that causes this.

…

On Thu, Apr 20, 2017 at 8:36 AM vaspas ***@***.***> wrote: Description Async.StartWithContinuations call is blocked when using AsyncSeq.BufferByCountAndTime in async operation. Repro steps let op = asyncSeq{ while true do yield 0 } |> AsyncSeq.bufferByCountAndTime 10 1000 |> AsyncSeq.iter (printf "%A ") let cts = new System.Threading.CancellationTokenSource() Async.StartWithContinuations(op, ignore, ignore, ignore, cts.Token) Expected behavior Async.StartWithContinuations call is returned Actual behavior Async.StartWithContinuations call blocks thread. Known workarounds Related information - Windows 10 - FSharp.Control.AsyncSeq (2.0.11) — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#65>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAlOdpq6zOYa0OmppUhxQYijT3oLSXeIks5rx1FQgaJpZM4NC97o> .

[eulerfx]

Hey, following up on this. It looks like the issue is the printf inside iter. This causes blocking even without bufferByTimeAndCount. If you instead call printfn then it works. If printfn is expanded it looks like this:

Printf.kfprintf (fun _ -> Console.Out.WriteLine()) Console.Out "%A" x

and printf is the same except the call to Console.Out.WriteLine(). So somehow, that calls unblocks the thread. If you instead call iterAsync and prepend with a call to do! Async.SwitchToThreadPool () then the thread is unblocked, however the still no printing.

Odd.

[vaspas]

Hello.

I have added waiting in example above.
Async.StartWithContinuations is returned then AsyncSeq.bufferByCountAndTime is excluded from pipeline.

[eulerfx]

To clarify my comment, things work as expected if you use printfn rather than printf..

[vaspas]

Only iterAsync with do! Async.SwitchToThreadPool () works for me.
printfn has the same blocking effect