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Preserve ExitCase in resources + fix memory leak #535

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Preserve ExitCase in resources + fix memory leak #535

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7a92ede
Preserve ExitCase in resources
kubukoz Mar 15, 2024
bb4c544
Fix compilation on 2.x
kubukoz Mar 15, 2024
d702cd2
Silence mima
kubukoz Mar 15, 2024
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1 change: 1 addition & 0 deletions build.sbt
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ lazy val core = crossProject(JVMPlatform, JSPlatform, NativePlatform)
ProblemFilters.exclude[DirectMissingMethodProblem]("org.typelevel.keypool.KeyPool.destroy"),
ProblemFilters.exclude[DirectMissingMethodProblem]("org.typelevel.keypool.KeyPool.reap"),
ProblemFilters.exclude[DirectMissingMethodProblem]("org.typelevel.keypool.KeyPool.put"),
ProblemFilters.exclude[IncompatibleMethTypeProblem]("org.typelevel.keypool.KeyPool.put"),
ProblemFilters
.exclude[DirectMissingMethodProblem]("org.typelevel.keypool.KeyPool#KeyPoolConcrete.this"),
ProblemFilters.exclude[DirectMissingMethodProblem](
Expand Down
114 changes: 65 additions & 49 deletions core/src/main/scala/org/typelevel/keypool/KeyPool.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ import cats.effect.std.Semaphore
import cats.syntax.all._
import scala.concurrent.duration._
import org.typelevel.keypool.internal._
import cats.effect.kernel.Resource.ExitCase

/**
* This pools internal guarantees are that the max number of values are in the pool at any time, not
Expand Down Expand Up @@ -68,7 +69,7 @@ object KeyPool {
private[keypool] val kpMaxIdle: Int,
private[keypool] val kpMaxTotal: Int,
private[keypool] val kpMaxTotalSem: Semaphore[F],
private[keypool] val kpVar: Ref[F, PoolMap[A, (B, F[Unit])]]
private[keypool] val kpVar: Ref[F, PoolMap[A, (B, ExitCase => F[Unit])]]
) extends KeyPool[F, A, B] {

def take(k: A): Resource[F, Managed[F, B]] =
Expand Down Expand Up @@ -115,37 +116,39 @@ object KeyPool {
* Make a 'KeyPool' inactive and destroy all idle resources.
*/
private[keypool] def destroy[F[_]: MonadThrow, A, B](
kpVar: Ref[F, PoolMap[A, (B, F[Unit])]]
): F[Unit] = for {
m <- kpVar.getAndSet(PoolMap.closed[A, (B, F[Unit])])
_ <- m match {
case PoolClosed() => Applicative[F].unit
case PoolOpen(_, m2) =>
m2.toList.traverse_ { case (_, pl) =>
pl.toList
.traverse_ { case (_, r) =>
r._2.attempt.void
}
}
}
} yield ()
kpVar: Ref[F, PoolMap[A, (B, ExitCase => F[Unit])]],
exit: ExitCase
): F[Unit] =
for {
m <- kpVar.getAndSet(PoolMap.closed[A, (B, ExitCase => F[Unit])])
_ <- m match {
case PoolClosed() => Applicative[F].unit
case PoolOpen(_, m2) =>
m2.toList.traverse_ { case (_, pl) =>
pl.toList
.traverse_ { case (_, r) =>
r._2(exit).attempt.void
}
}
}
} yield ()

/**
* Run a reaper thread, which will destroy old resources. It will stop running once our pool
* switches to PoolClosed.
*/
private[keypool] def reap[F[_], A, B](
idleTimeAllowedInPoolNanos: FiniteDuration,
kpVar: Ref[F, PoolMap[A, (B, F[Unit])]],
kpVar: Ref[F, PoolMap[A, (B, ExitCase => F[Unit])]],
onReaperException: Throwable => F[Unit]
)(implicit F: Temporal[F]): F[Unit] = {
// We are going to do non-referentially transparent things as we may be waiting for our modification to go through
// which may change the state depending on when the modification block is running atomically at the moment
def findStale(
now: FiniteDuration,
idleCount: Int,
m: Map[A, PoolList[(B, F[Unit])]]
): (PoolMap[A, (B, F[Unit])], List[(A, (B, F[Unit]))]) = {
m: Map[A, PoolList[(B, ExitCase => F[Unit])]]
): (PoolMap[A, (B, ExitCase => F[Unit])], List[(A, (B, ExitCase => F[Unit]))]) = {
val isNotStale: FiniteDuration => Boolean =
time =>
time + idleTimeAllowedInPoolNanos >= now // Time value is alright inside the KeyPool in nanos.
Expand All @@ -157,19 +160,24 @@ object KeyPool {
// (Map key (PoolList resource), [resource])
@annotation.tailrec
def findStale_(
toKeep: List[(A, PoolList[(B, F[Unit])])] => List[(A, PoolList[(B, F[Unit])])],
toDestroy: List[(A, (B, F[Unit]))] => List[(A, (B, F[Unit]))],
l: List[(A, PoolList[(B, F[Unit])])]
): (Map[A, PoolList[(B, F[Unit])]], List[(A, (B, F[Unit]))]) = {
toKeep: List[(A, PoolList[(B, ExitCase => F[Unit])])] => List[
(A, PoolList[(B, ExitCase => F[Unit])])
],
toDestroy: List[(A, (B, ExitCase => F[Unit]))] => List[(A, (B, ExitCase => F[Unit]))],
l: List[(A, PoolList[(B, ExitCase => F[Unit])])]
): (Map[A, PoolList[(B, ExitCase => F[Unit])]], List[(A, (B, ExitCase => F[Unit]))]) = {
l match {
case Nil => (toKeep(List.empty).toMap, toDestroy(List.empty))
case (key, pList) :: rest =>
// Can use span since we know everything will be ordered as the time is
// when it is placed back into the pool.
val (notStale, stale) = pList.toList.span(r => isNotStale(r._1))
val toDestroy_ : List[(A, (B, F[Unit]))] => List[(A, (B, F[Unit]))] = l =>
toDestroy(stale.map(t => key -> t._2) ++ l)
val toKeep_ : List[(A, PoolList[(B, F[Unit])])] => List[(A, PoolList[(B, F[Unit])])] =
val toDestroy_ : List[(A, (B, ExitCase => F[Unit]))] => List[
(A, (B, ExitCase => F[Unit]))
] = l => toDestroy(stale.map(t => key -> t._2) ++ l)
val toKeep_ : List[(A, PoolList[(B, ExitCase => F[Unit])])] => List[
(A, PoolList[(B, ExitCase => F[Unit])])
] =
l =>
PoolList.fromList(notStale) match {
case None => toKeep(l)
Expand All @@ -187,9 +195,8 @@ object KeyPool {
val sleep = Temporal[F].sleep(5.seconds).void

// Wait 5 Seconds
def loop: F[Unit] = for {
now <- Temporal[F].monotonic
_ <- {
def loop: F[Unit] = Temporal[F].monotonic
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@kubukoz kubukoz Mar 15, 2024 •
edited
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thought: this change also avoids a memory leak on Scala 3 (due to better-monadic-for not eliminating the final map).

tl;dr previously it was

def loop = for {
  x <- fx
  _ <- (somethingSomething >> loop)
} yield ()

which desugars to

fx.flatMap { x => (somethingSomething >> loop).map(_ => ()) }

which allocates a Map node on every run and never cleans it up (the same goes for the top-level flatMap, and apparently the lambdas too).

Proof: run this for a minute or so.

//> using dep "org.typelevel::cats-effect:3.5.3"
import cats.effect.*

def loop: IO[Unit] = for {
  _ <- IO.unit
  _ <- IO.unit >> loop
} yield ()

object CatsDemo extends IOApp.Simple {
  def run = loop
}
image

.flatMap { now =>
kpVar.tryModify {
case p @ PoolClosed() => (p, F.unit)
case p @ PoolOpen(idleCount, m) =>
Expand All @@ -199,25 +206,26 @@ object KeyPool {
val (m_, toDestroy) = findStale(now, idleCount, m)
(
m_,
toDestroy.traverse_(_._2._2).attempt.flatMap {
// In this context, we're closing the resource due to it not being used for a while - hence a Succeeded exit case.
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thought: special case here: everywhere else we have an ExitCase to propagate, but the reaper deliberately closes resources out of thin air: I figured Succeeded makes the most sense for a resource that's no longer necessary. Canceled didn't sound right, but happy to discuss if anyone disagrees

toDestroy.traverse_(_._2._2(ExitCase.Succeeded)).attempt.flatMap {
case Left(t) => onReaperException(t)
// .handleErrorWith(t => F.delay(t.printStackTrace())) // CHEATING?
case Right(()) => F.unit
}
)
}
}
}.flatMap {
}
.flatMap {
case Some(act) => act >> sleep >> loop
case None => loop
}
} yield ()

loop
}

private[keypool] def state[F[_]: Functor, A, B](
kpVar: Ref[F, PoolMap[A, (B, F[Unit])]]
kpVar: Ref[F, PoolMap[A, (B, ExitCase => F[Unit])]]
): F[(Int, Map[A, Int])] =
kpVar.get.map {
case PoolClosed() =>
Expand All @@ -237,8 +245,8 @@ object KeyPool {
kp: KeyPoolConcrete[F, A, B],
k: A,
r: B,
destroy: F[Unit]
): F[Unit] = {
destroy: ExitCase => F[Unit]
): ExitCase => F[Unit] = {
def addToList[Z](
now: FiniteDuration,
maxCount: Int,
Expand All @@ -254,7 +262,10 @@ object KeyPool {
else (l, Some(x))
}
}
def go(now: FiniteDuration, pc: PoolMap[A, (B, F[Unit])]): (PoolMap[A, (B, F[Unit])], F[Unit]) =
def go(
now: FiniteDuration,
pc: PoolMap[A, (B, ExitCase => F[Unit])]
): (PoolMap[A, (B, ExitCase => F[Unit])], ExitCase => F[Unit]) =
pc match {
case p @ PoolClosed() => (p, destroy)
case p @ PoolOpen(idleCount, m) =>
Expand All @@ -264,25 +275,28 @@ object KeyPool {
case None =>
val cnt_ = idleCount + 1
val m_ = PoolMap.open(cnt_, m + (k -> One((r, destroy), now)))
(m_, Applicative[F].pure(()))
(m_, Function.const[F[Unit], ExitCase](Applicative[F].unit))
case Some(l) =>
val (l_, mx) = addToList(now, kp.kpMaxPerKey(k), (r, destroy), l)
val cnt_ = idleCount + mx.fold(1)(_ => 0)
val m_ = PoolMap.open(cnt_, m + (k -> l_))
(m_, mx.fold(Applicative[F].unit)(_ => destroy))
(m_, mx.fold((_: ExitCase) => Applicative[F].unit)(_ => destroy))
}
}

Clock[F].monotonic.flatMap { now =>
kp.kpVar.modify(pm => go(now, pm)).flatten
}
(exit: ExitCase) =>
Clock[F].monotonic.flatMap { now =>
kp.kpVar.modify(pm => go(now, pm)).flatMap(_(exit))
}
}

private[keypool] def take[F[_]: Temporal, A, B](
kp: KeyPoolConcrete[F, A, B],
k: A
): Resource[F, Managed[F, B]] = {
def go(pm: PoolMap[A, (B, F[Unit])]): (PoolMap[A, (B, F[Unit])], Option[(B, F[Unit])]) =
def go(
pm: PoolMap[A, (B, ExitCase => F[Unit])]
): (PoolMap[A, (B, ExitCase => F[Unit])], Option[(B, ExitCase => F[Unit])]) =
pm match {
case p @ PoolClosed() => (p, None)
case pOrig @ PoolOpen(idleCount, m) =>
Expand All @@ -299,14 +313,14 @@ object KeyPool {
_ <- kp.kpMaxTotalSem.permit
optR <- Resource.eval(kp.kpVar.modify(go))
releasedState <- Resource.eval(Ref[F].of[Reusable](kp.kpDefaultReuseState))
resource <- Resource.makeFull[F, (B, F[Unit])] { poll =>
optR.fold(poll(kp.kpRes(k).allocated))(r => Applicative[F].pure(r))
} { resource =>
resource <- Resource.makeCaseFull[F, (B, ExitCase => F[Unit])] { poll =>
optR.fold(poll(kp.kpRes(k).allocatedCase))(r => Applicative[F].pure(r))
} { (resource, exitCase) =>
for {
reusable <- releasedState.get
out <- reusable match {
case Reusable.Reuse => put(kp, k, resource._1, resource._2).attempt.void
case Reusable.DontReuse => resource._2.attempt.void
case Reusable.Reuse => put(kp, k, resource._1, resource._2).apply(exitCase).attempt.void
case Reusable.DontReuse => resource._2(exitCase).attempt.void
}
} yield out
}
Expand Down Expand Up @@ -370,9 +384,11 @@ object KeyPool {
def keepRunning[Z](fa: F[Z]): F[Z] =
fa.onError { case e => onReaperException(e) }.attempt >> keepRunning(fa)
for {
kpVar <- Resource.make(
Ref[F].of[PoolMap[A, (B, F[Unit])]](PoolMap.open(0, Map.empty[A, PoolList[(B, F[Unit])]]))
)(kpVar => KeyPool.destroy(kpVar))
kpVar <- Resource.makeCase(
Ref[F].of[PoolMap[A, (B, ExitCase => F[Unit])]](
PoolMap.open(0, Map.empty[A, PoolList[(B, ExitCase => F[Unit])]])
)
)(KeyPool.destroy)
kpMaxTotalSem <- Resource.eval(Semaphore[F](kpMaxTotal.toLong))
_ <- idleTimeAllowedInPool match {
case fd: FiniteDuration =>
Expand Down
9 changes: 6 additions & 3 deletions core/src/main/scala/org/typelevel/keypool/KeyPoolBuilder.scala
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Expand Up @@ -28,6 +28,7 @@ import cats.effect.kernel._
import cats.effect.kernel.syntax.spawn._
import cats.effect.std.Semaphore
import scala.concurrent.duration._
import cats.effect.kernel.Resource.ExitCase

@deprecated("use KeyPool.Builder", "0.4.7")
final class KeyPoolBuilder[F[_]: Temporal, A, B] private (
Expand Down Expand Up @@ -88,9 +89,11 @@ final class KeyPoolBuilder[F[_]: Temporal, A, B] private (
def keepRunning[Z](fa: F[Z]): F[Z] =
fa.onError { case e => onReaperException(e) }.attempt >> keepRunning(fa)
for {
kpVar <- Resource.make(
Ref[F].of[PoolMap[A, (B, F[Unit])]](PoolMap.open(0, Map.empty[A, PoolList[(B, F[Unit])]]))
)(kpVar => KeyPool.destroy(kpVar))
kpVar <- Resource.makeCase(
Ref[F].of[PoolMap[A, (B, ExitCase => F[Unit])]](
PoolMap.open(0, Map.empty[A, PoolList[(B, ExitCase => F[Unit])]])
)
)(KeyPool.destroy)
kpMaxTotalSem <- Resource.eval(Semaphore[F](kpMaxTotal.toLong))
_ <- idleTimeAllowedInPool match {
case fd: FiniteDuration =>
Expand Down