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Fix #4627 resource early cancelation #4630

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Fix #4627 resource early cancelation #4630

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8da0407
Fix #4627 resource early cancelation
reardonj Jul 5, 2026
81c246d
narrow usages of poll in Resource
reardonj Jul 6, 2026
461008f
Resource orElse is not like combineK
reardonj Jul 19, 2026
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128 changes: 65 additions & 63 deletions kernel/shared/src/main/scala/cats/effect/kernel/Resource.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -161,38 +161,41 @@ sealed abstract class Resource[F[_], +A] extends Serializable {
case object Nil extends Stack[A]
final case class Frame[AA, BB](head: AA => Resource[F, BB], tail: Stack[BB])
extends Stack[AA]
F.uncancelable { poll =>
// Indirection for calling `loop` needed because `loop` must be @tailrec
def continue[C](current: Resource[F, C], stack: Stack[C]): F[B] =
loop(current, stack)

// Interpreter that knows how to evaluate a Resource data structure;
// Maintains its own stack for dealing with Bind chains
@tailrec def loop[C](current: Resource[F, C], stack: Stack[C]): F[B] =
current match {
case Allocate(resource) =>
F.bracketFull(p => p(resource(poll))) {
case (a, _) =>
stack match {
case Nil => poll(onOutput(a))
case Frame(head, tail) => continue(head(a), tail)
}
} {
case ((_, release), outcome) =>
onRelease(release, ExitCase.fromOutcome(outcome))
}
case Bind(source, fs) =>
loop(source, Frame(fs, stack))
case Pure(v) =>
stack match {
case Nil => poll(onOutput(v))
case Frame(head, tail) =>
loop(head(v), tail)
}
case Eval(fa) =>
poll(fa).flatMap(a => continue(Resource.pure(a), stack))
}

// Indirection for calling `loop` needed because `loop` must be @tailrec
def continue[C](current: Resource[F, C], stack: Stack[C]): F[B] =
loop(current, stack)

// Interpreter that knows how to evaluate a Resource data structure;
// Maintains its own stack for dealing with Bind chains
@tailrec def loop[C](current: Resource[F, C], stack: Stack[C]): F[B] =
current match {
case Allocate(resource) =>
F.bracketFull(resource) {
case (a, _) =>
stack match {
case Nil => onOutput(a)
case Frame(head, tail) => continue(head(a), tail)
}
} {
case ((_, release), outcome) =>
onRelease(release, ExitCase.fromOutcome(outcome))
}
case Bind(source, fs) =>
loop(source, Frame(fs, stack))
case Pure(v) =>
stack match {
case Nil => onOutput(v)
case Frame(head, tail) =>
loop(head(v), tail)
}
case Eval(fa) =>
fa.flatMap(a => continue(Resource.pure(a), stack))
}
loop(this, Nil)
loop(this, Nil)

}
}

/**
Expand Down Expand Up @@ -467,23 +470,22 @@ sealed abstract class Resource[F[_], +A] extends Serializable {
case object Nil extends Stack[B]
final case class Frame[AA, BB](head: AA => Resource[F, BB], tail: Stack[BB])
extends Stack[AA]

// Indirection for calling `loop` needed because `loop` must be @tailrec
def continue[C](
current: Resource[F, C],
stack: Stack[C],
release: ExitCase => F[Unit]): F[(B, ExitCase => F[Unit])] =
loop(current, stack, release)

// Interpreter that knows how to evaluate a Resource data structure;
// Maintains its own stack for dealing with Bind chains
@tailrec def loop[C](
current: Resource[F, C],
stack: Stack[C],
release: ExitCase => F[Unit]): F[(B, ExitCase => F[Unit])] =
current match {
case Allocate(resource) =>
F uncancelable { poll =>
F uncancelable { poll =>
// Indirection for calling `loop` needed because `loop` must be @tailrec
def continue[C](
current: Resource[F, C],
stack: Stack[C],
release: ExitCase => F[Unit]): F[(B, ExitCase => F[Unit])] =
loop(current, stack, release)

// Interpreter that knows how to evaluate a Resource data structure;
// Maintains its own stack for dealing with Bind chains
@tailrec def loop[C](
current: Resource[F, C],
stack: Stack[C],
release: ExitCase => F[Unit]): F[(B, ExitCase => F[Unit])] =
current match {
case Allocate(resource) =>
resource(poll) flatMap {
case (b, rel) =>
// Insert F.unit to emulate defer for stack-safety
Expand All @@ -505,29 +507,29 @@ sealed abstract class Resource[F[_], +A] extends Serializable {
F.pure((b, rel2))

case Frame(head, tail) =>
poll(continue(head(b), tail, rel2))
(poll(F.unit) >> continue(head(b), tail, rel2))
.onCancel(rel(ExitCase.Canceled))
.onError { case e => rel(ExitCase.Errored(e)).handleError(_ => ()) }
}
}
}

case Bind(source, fs) =>
loop(source, Frame(fs, stack), release)
case Bind(source, fs) =>
loop(source, Frame(fs, stack), release)

case Pure(v) =>
stack match {
case Nil =>
(v: B, release).pure[F]
case Frame(head, tail) =>
loop(head(v), tail, release)
}
case Pure(v) =>
stack match {
case Nil =>
(v: B, release).pure[F]
case Frame(head, tail) =>
loop(head(v), tail, release)
}

case Eval(fa) =>
fa.flatMap(a => continue(Resource.pure(a), stack, release))
}
case Eval(fa) =>
poll(fa).flatMap(a => continue(Resource.pure(a), stack, release))
}

loop(this, Nil, _ => F.unit)
loop(this, Nil, _ => F.unit)
}
}

/**
Expand Down
30 changes: 20 additions & 10 deletions tests/shared/src/test/scala/cats/effect/ResourceSuite.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,26 @@ class ResourceSuite extends BaseScalaCheckSuite with DisciplineSuite {
forAll { (fa: IO[String]) => assertEqv(Resource.eval(fa).use(IO.pure), fa) }
}

real("eval - uncancelable timeout is not canceled") {
Resource.eval(IO.uncancelable(_ => IO.sleep(100.millis))).timeout(10.millis).use_
}

real("eval - uncancelable continuation") {
val res = Resource
.make(IO.pure(42))(_ => IO.unit)
.flatMap(_ => Resource.eval(IO.uncancelable { _ => IO.canceled }))

for {
ctr <- IO.ref(0)
fib <- IO.uncancelable { poll =>
poll(res.allocatedCase).flatMap { _ => ctr.update(_ + 1) }
}.start
_ <- fib.join
c <- ctr.get
_ <- IO { assertEquals(c, 1) }
} yield ()
}

ticked("eval - interruption") { implicit ticker =>
def resource(d: Deferred[IO, Int]): Resource[IO, Unit] =
for {
Expand Down Expand Up @@ -722,16 +742,6 @@ class ResourceSuite extends BaseScalaCheckSuite with DisciplineSuite {
assertEquals(released, acquired)
}

tickedProperty("combineK - behave like orElse when underlying effect does") {
implicit ticker =>
forAll { (r1: Resource[IO, Int], r2: Resource[IO, Int]) =>
val lhs = r1.orElse(r2)
val rhs = r1 <+> r2

assertEqv(lhs, rhs)
}
}

tickedProperty("combineK - behave like underlying effect") { implicit ticker =>
forAll { (ot1: OptionT[IO, Int], ot2: OptionT[IO, Int]) =>
val lhs = Resource.eval(ot1 <+> ot2).use(OptionT.pure[IO](_)).value
Expand Down
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