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Fix cancelation leak in fromFuture, fromFutureCancelable #3892

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merged 12 commits into from
Nov 23, 2023
Merged

Fix cancelation leak in fromFuture, fromFutureCancelable #3892

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e9bf16d
Fix leak in fromFutureCancelable
TimWSpence Nov 9, 2023
4d0a3c9
Attempt to fix leak in fromFuture as well
TimWSpence Nov 9, 2023
76b8026
Avoid leaking future in fromFutureCancelable and reduce opportunity for
TimWSpence Nov 17, 2023
6b25b6d
Fix leaks in Async#fromFuture plus tests
TimWSpence Nov 22, 2023
22effa2
Rewrite fromFuture test using TestControl ala existing
TimWSpence Nov 22, 2023
361ca8f
Fix Async#fromFutureCancelable
TimWSpence Nov 23, 2023
a9fb7b3
scalafixAll
TimWSpence Nov 23, 2023
73eb17b
Make async node cancelable in Async#fromFutureCancelable
TimWSpence Nov 23, 2023
38a2919
Fix new cancelation leak
TimWSpence Nov 23, 2023
36f1d8d
scalafixAll
TimWSpence Nov 23, 2023
7229547
Turns out bug is reproducible with TestControl
TimWSpence Nov 23, 2023
77c404a
One day I will remember to run scalafix
TimWSpence Nov 23, 2023
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18 changes: 10 additions & 8 deletions kernel/shared/src/main/scala/cats/effect/kernel/Async.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -212,21 +212,23 @@ trait Async[F[_]] extends AsyncPlatform[F] with Sync[F] with Temporal[F] {
* [[fromFutureCancelable]] for a cancelable version
*/
def fromFuture[A](fut: F[Future[A]]): F[A] =
flatMap(fut) { f =>
flatMap(executionContext) { implicit ec =>
async_[A](cb => f.onComplete(t => cb(t.toEither)))
async_[A] { cb =>
flatMap(fut) { f =>
map(executionContext) { implicit ec => f.onComplete(t => cb(t.toEither)) }
}
}

/**
* Like [[fromFuture]], but is cancelable via the provided finalizer.
*/
def fromFutureCancelable[A](futCancel: F[(Future[A], F[Unit])]): F[A] =
flatMap(futCancel) {
case (fut, fin) =>
flatMap(executionContext) { implicit ec =>
async[A](cb => as(delay(fut.onComplete(t => cb(t.toEither))), Some(fin)))
}
async[A] { cb =>
flatMap(futCancel) {
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I think we have to use uncancelable+poll. Otherwise starting the Future with futCancel is not cancelable, and it can be. It's only after we've started it, that we need guarantee the async is setup appropriately.

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I hope that is sufficient anyway, otherwise we'd have to drop down to cont 😬

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Well I did only say that I'd fix the leak 😛

Yeah I was wondering about that as I wrote it. I'll give it a go with uncancelable/poll. Although I did notice that in AsyncPlatform#fromCompletableFuture we changed it to use cont. I don't suppose you remember why?

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I don't suppose you remember why?

That's because the cancelation protocol for CompletableFuture is more complex: even if you request cancelation, it may indicate to you that it hasn't canceled in which case you need to fallback to waiting for the result. The best way to express this is with cont.

(Aside, but CE doesn't really handle this well, we still have leaks even in the cont-based implementation #3474).

case (fut, fin) =>
flatMap(executionContext) { implicit ec =>
as(delay(fut.onComplete(t => cb(t.toEither))), Some(fin))
}
}
}

/**
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