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Update MacOS and Fix Async Cont get cancellation race #4713

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Update MacOS and Fix Async Cont get cancellation race #4713

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a2b8776
Fix Async Cont get cancellation race
reardonj Nov 6, 2026
9f5a48c
run build on macos-15
reardonj Nov 7, 2026
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24 changes: 12 additions & 12 deletions .github/workflows/ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ jobs:
- ubuntu-latest
- ubuntu-22.04-arm
- windows-2022
- macos-14
- macos-15
scala: [3.3.4, 2.12.20, 2.13.18]
java:
- temurin@8
Expand Down Expand Up @@ -64,18 +64,18 @@ jobs:
- os: windows-2022
scala: 3.3.4
ci: ciJVM
- os: macos-14
- os: macos-15
scala: 3.3.4
ci: ciJVM
- os: windows-2022
scala: 2.12.20
ci: ciJVM
- os: macos-14
- os: macos-15
scala: 2.12.20
ci: ciJVM
- os: macos-14
- os: macos-15
java: temurin@8
- os: macos-14
- os: macos-15
java: temurin@11
- ci: ciFirefox
scala: 3.3.4
Expand All @@ -97,7 +97,7 @@ jobs:
ci: ciJS
- os: windows-2022
ci: ciJS
- os: macos-14
- os: macos-15
ci: ciJS
- ci: ciFirefox
java: temurin@11
Expand All @@ -111,7 +111,7 @@ jobs:
ci: ciFirefox
- os: windows-2022
ci: ciFirefox
- os: macos-14
- os: macos-15
ci: ciFirefox
- ci: ciChrome
java: temurin@11
Expand All @@ -125,7 +125,7 @@ jobs:
ci: ciChrome
- os: windows-2022
ci: ciChrome
- os: macos-14
- os: macos-15
ci: ciChrome
- ci: ciNative
java: temurin@11
Expand All @@ -138,7 +138,7 @@ jobs:
os: windows-2022
- ci: ciNative
java: temurin@11
os: macos-14
os: macos-15
- ci: ciNative
java: temurin@17
os: ubuntu-latest
Expand All @@ -156,7 +156,7 @@ jobs:
os: windows-2022
- ci: ciNative
java: temurin@21
os: macos-14
os: macos-15
- ci: ciNative
java: graalvm@21
os: ubuntu-latest
Expand All @@ -168,13 +168,13 @@ jobs:
os: windows-2022
- ci: ciNative
java: graalvm@21
os: macos-14
os: macos-15
- os: ubuntu-22.04-arm
ci: ciNative
scala: 2.12.20
- os: windows-2022
ci: ciNative
- os: macos-14
- os: macos-15
ci: ciNative
scala: 2.12.20
runs-on: ${{ matrix.os }}
Expand Down
2 changes: 1 addition & 1 deletion build.sbt
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ ThisBuild / developers := List(
val PrimaryOS = "ubuntu-latest"
val ArmOS = "ubuntu-22.04-arm"
val Windows = "windows-2022"
val MacOS = "macos-14"
val MacOS = "macos-15"

val Scala212 = "2.12.20"
val Scala213 = "2.13.18"
Expand Down
18 changes: 11 additions & 7 deletions core/shared/src/main/scala/cats/effect/IOFiber.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -785,20 +785,24 @@ private final class IOFiber[A](
finalizers.push(fin)
conts = ByteStack.push(conts, OnCancelK)

/*
* We set the finalizing check to the *suspension* point, which may
* be in a different finalizer scope than the cont itself. This must be
* written before publishing "waiting", or a racing `cb` could see a
* stale value from an earlier `get` and drop the wakeup.
* `wasFinalizing` is published by a volatile store on `suspended`, below.
*/
if (state.get() eq null) {
state.wasFinalizing = finalizing
}

if (state.compareAndSet(null, state.waiting)) {
/*
* `state` was "initial" (null), so `get` has arrived before the callback,
* it needs to set the state to "waiting" and suspend: `cb` will
* resume with the result once that's ready
*/

/*
* we set the finalizing check to the *suspension* point, which may
* be in a different finalizer scope than the cont itself.
* `wasFinalizing` is published by a volatile store on `suspended`.
*/
state.wasFinalizing = finalizing

if (isStackTracing) {
state.handle = monitor()
finalizers.push(IO {
Expand Down
20 changes: 20 additions & 0 deletions tests/shared/src/test/scala/cats/effect/IOSuite.scala
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Expand Up @@ -1106,6 +1106,26 @@ class IOSuite extends BaseScalaCheckSuite with DisciplineSuite with IOPlatformSu
} yield result
}

// a second `get` in a finalizer must not miss a callback that races with cancelation
real("cont - second get in onCancel finalizer does not hang") {
val cont = IO.cont[Unit, Unit](new Cont[IO, Unit, Unit] {
def apply[G[_]](implicit G: MonadCancel[G, Throwable]) = { (resume, get, lift) =>
G.uncancelable { poll =>
lift(IO.cede.productR(IO(resume(Right(())))).start) *>
poll(get).onCancel(get)
}
}
})

val one = for {
fiber <- cont.start
_ <- IO.cede
_ <- fiber.cancel
} yield ()

one.parReplicateA_(if (!isJS) 8 else 1).replicateA_(50000)

@reardonj reardonj Nov 7, 2026

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This does take a significant number of tries to fail locally.

}

ticked("async - allow for misordered nesting") { implicit ticker =>
var outerR = 0
var innerR = 0
Expand Down
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