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KeyPool.scala
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KeyPool.scala
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/*
* Copyright (c) 2019 Typelevel
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package org.typelevel.keypool
import cats._
import cats.effect.kernel._
import cats.effect.kernel.syntax.spawn._
import cats.effect.std.Semaphore
import cats.syntax.all._
import scala.concurrent.duration._
import org.typelevel.keypool.internal._
/**
* This pools internal guarantees are that the max number of values are in the pool at any time, not
* maximum number of operations. To do the latter application level bounds should be used.
*
* A background reaper thread is kept alive for the length of the key pools life.
*
* When resources are taken from the pool they are received as a [[Managed]]. This [[Managed]] has a
* Ref to a [[Reusable]] which indicates whether or not the pool can reuse the resource.
*/
trait KeyPool[F[_], A, B] {
/**
* Take a [[Managed]] from the Pool. For the lifetime of this resource this is exclusively
* available to this key.
*
* At the end of the resource lifetime the state of the resource controls whether it is submitted
* back to the pool or removed.
*/
def take(k: A): Resource[F, Managed[F, B]]
/**
* The current state of the pool.
*
* The left value is the total number of resources currently in the pool, and the right is a map
* of how many resources exist for each key.
*/
def state: F[(Int, Map[A, Int])]
}
object KeyPool {
private[keypool] final class KeyPoolConcrete[F[_]: Temporal, A, B] private[keypool] (
private[keypool] val kpRes: A => Resource[F, B],
private[keypool] val kpDefaultReuseState: Reusable,
private[keypool] val kpMaxPerKey: A => Int,
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])]]
) extends KeyPool[F, A, B] {
def take(k: A): Resource[F, Managed[F, B]] =
KeyPool.take(this, k)
def state: F[(Int, Map[A, Int])] =
KeyPool.state(kpVar)
}
//
// Instances
//
implicit def keypoolFunctor[F[_], Z]: Functor[KeyPool[F, Z, *]] =
new KPFunctor[F, Z]
private class KPFunctor[F[_], Z] extends Functor[KeyPool[F, Z, *]] {
override def map[A, B](fa: KeyPool[F, Z, A])(f: A => B): KeyPool[F, Z, B] =
new KeyPool[F, Z, B] {
def take(k: Z): Resource[F, Managed[F, B]] =
fa.take(k).map(_.map(f))
def state: F[(Int, Map[Z, Int])] = fa.state
}
}
// Instance Is an AlleyCat Due to Map Functor instance
// Must Explicitly Import
def keypoolInvariant[F[_]: Functor, Z]: Invariant[KeyPool[F, *, Z]] =
new KPInvariant[F, Z]
private class KPInvariant[F[_]: Functor, Z] extends Invariant[KeyPool[F, *, Z]] {
override def imap[A, B](fa: KeyPool[F, A, Z])(f: A => B)(g: B => A): KeyPool[F, B, Z] =
new KeyPool[F, B, Z] {
def take(k: B): Resource[F, Managed[F, Z]] =
fa.take(g(k))
def state: F[(Int, Map[B, Int])] = fa.state.map { case (total, m) =>
(total, m.map { case (a, i) => (f(a), i) })
}
}
}
// Internal Helpers
/**
* 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 ()
/**
* 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])]],
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]))]) = {
val isNotStale: FiniteDuration => Boolean =
time =>
time + idleTimeAllowedInPoolNanos >= now // Time value is alright inside the KeyPool in nanos.
// Probably a more idiomatic way to do this in scala
// ([(key, PoolList resource)] -> [(key, PoolList resource)]) ->
// ([resource] -> [resource]) ->
// [(key, PoolList resource)] ->
// (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]))]) = {
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])])] =
l =>
PoolList.fromList(notStale) match {
case None => toKeep(l)
case Some(x) => toKeep((key, x) :: l)
}
findStale_(toKeep_, toDestroy_, rest)
}
}
// May be able to use Span eventually
val (toKeep, toDestroy) = findStale_(identity, identity, m.toList)
val idleCount_ = idleCount - toDestroy.length
(PoolMap.open(idleCount_, toKeep), toDestroy)
}
val sleep = Temporal[F].sleep(5.seconds).void
// Wait 5 Seconds
def loop: F[Unit] = for {
now <- Temporal[F].monotonic
_ <- {
kpVar.tryModify {
case p @ PoolClosed() => (p, F.unit)
case p @ PoolOpen(idleCount, m) =>
if (m.isEmpty)
(p, F.unit) // Not worth it to introduce deadlock concerns when hot loop is 5 seconds
else {
val (m_, toDestroy) = findStale(now, idleCount, m)
(
m_,
toDestroy.traverse_(_._2._2).attempt.flatMap {
case Left(t) => onReaperException(t)
// .handleErrorWith(t => F.delay(t.printStackTrace())) // CHEATING?
case Right(()) => F.unit
}
)
}
}
}.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])]]
): F[(Int, Map[A, Int])] =
kpVar.get.map {
case PoolClosed() =>
(0, Map.empty)
case PoolOpen(idleCount, m) =>
val modified = m.map { case (k, pl) =>
pl match {
case One(_, _) => (k, 1)
case Cons(_, length, _, _) => (k, length)
}
}
(idleCount, modified)
}
private[keypool] def put[F[_]: Temporal, A, B](
kp: KeyPoolConcrete[F, A, B],
k: A,
r: B,
destroy: F[Unit]
): F[Unit] = {
def addToList[Z](
now: FiniteDuration,
maxCount: Int,
x: Z,
l: PoolList[Z]
): (PoolList[Z], Option[Z]) =
if (maxCount <= 1) (l, Some(x))
else {
l match {
case l @ One(_, _) => (Cons(x, 2, now, l), None)
case l @ Cons(_, currCount, _, _) =>
if (maxCount > currCount) (Cons(x, currCount + 1, now, l), None)
else (l, Some(x))
}
}
def go(now: FiniteDuration, pc: PoolMap[A, (B, F[Unit])]): (PoolMap[A, (B, F[Unit])], F[Unit]) =
pc match {
case p @ PoolClosed() => (p, destroy)
case p @ PoolOpen(idleCount, m) =>
if (idleCount > kp.kpMaxIdle) (p, destroy)
else
m.get(k) match {
case None =>
val cnt_ = idleCount + 1
val m_ = PoolMap.open(cnt_, m + (k -> One((r, destroy), now)))
(m_, Applicative[F].pure(()))
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))
}
}
Clock[F].monotonic.flatMap { now =>
kp.kpVar.modify(pm => go(now, pm)).flatten
}
}
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])]) =
pm match {
case p @ PoolClosed() => (p, None)
case pOrig @ PoolOpen(idleCount, m) =>
m.get(k) match {
case None => (pOrig, None)
case Some(One(a, _)) =>
(PoolMap.open(idleCount - 1, m - k), Some(a))
case Some(Cons(a, _, _, rest)) =>
(PoolMap.open(idleCount - 1, m + (k -> rest)), Some(a))
}
}
for {
_ <- kp.kpMaxTotalSem.permit
optR <- Resource.eval(kp.kpVar.modify(go))
releasedState <- Resource.eval(Ref[F].of[Reusable](kp.kpDefaultReuseState))
resource <- Resource.make(optR.fold(kp.kpRes(k).allocated)(r => Applicative[F].pure(r))) {
resource =>
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
}
} yield out
}
} yield new Managed(resource._1, optR.isDefined, releasedState)
}
final class Builder[F[_]: Temporal, A, B] private[keypool] (
val kpRes: A => Resource[F, B],
val kpDefaultReuseState: Reusable,
val idleTimeAllowedInPool: Duration,
val kpMaxPerKey: A => Int,
val kpMaxIdle: Int,
val kpMaxTotal: Int,
val onReaperException: Throwable => F[Unit]
) {
private def copy(
kpRes: A => Resource[F, B] = this.kpRes,
kpDefaultReuseState: Reusable = this.kpDefaultReuseState,
idleTimeAllowedInPool: Duration = this.idleTimeAllowedInPool,
kpMaxPerKey: A => Int = this.kpMaxPerKey,
kpMaxIdle: Int = this.kpMaxIdle,
kpMaxTotal: Int = this.kpMaxTotal,
onReaperException: Throwable => F[Unit] = this.onReaperException
): Builder[F, A, B] = new Builder[F, A, B](
kpRes,
kpDefaultReuseState,
idleTimeAllowedInPool,
kpMaxPerKey,
kpMaxIdle,
kpMaxTotal,
onReaperException
)
def doOnCreate(f: B => F[Unit]): Builder[F, A, B] =
copy(kpRes = { (k: A) => this.kpRes(k).flatMap(v => Resource.eval(f(v).attempt.void.as(v))) })
def doOnDestroy(f: B => F[Unit]): Builder[F, A, B] =
copy(kpRes = { (k: A) =>
this.kpRes(k).flatMap(v => Resource.make(Applicative[F].unit)(_ => f(v).attempt.void).as(v))
})
def withDefaultReuseState(defaultReuseState: Reusable): Builder[F, A, B] =
copy(kpDefaultReuseState = defaultReuseState)
def withIdleTimeAllowedInPool(duration: Duration): Builder[F, A, B] =
copy(idleTimeAllowedInPool = duration)
def withMaxPerKey(f: A => Int): Builder[F, A, B] =
copy(kpMaxPerKey = f)
def withMaxIdle(maxIdle: Int): Builder[F, A, B] =
copy(kpMaxIdle = maxIdle)
def withMaxTotal(total: Int): Builder[F, A, B] =
copy(kpMaxTotal = total)
def withOnReaperException(f: Throwable => F[Unit]): Builder[F, A, B] =
copy(onReaperException = f)
def build: Resource[F, KeyPool[F, A, B]] = {
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))
kpMaxTotalSem <- Resource.eval(Semaphore[F](kpMaxTotal.toLong))
_ <- idleTimeAllowedInPool match {
case fd: FiniteDuration =>
val nanos = 0.seconds.max(fd)
keepRunning(KeyPool.reap(nanos, kpVar, onReaperException)).background.void
case _ =>
Applicative[Resource[F, *]].unit
}
} yield new KeyPool.KeyPoolConcrete(
kpRes,
kpDefaultReuseState,
kpMaxPerKey,
kpMaxIdle,
kpMaxTotal,
kpMaxTotalSem,
kpVar
)
}
}
object Builder {
def apply[F[_]: Temporal, A, B](
res: A => Resource[F, B]
): Builder[F, A, B] = new Builder[F, A, B](
res,
Defaults.defaultReuseState,
Defaults.idleTimeAllowedInPool,
Defaults.maxPerKey,
Defaults.maxIdle,
Defaults.maxTotal,
Defaults.onReaperException[F]
)
def apply[F[_]: Temporal, A, B](
create: A => F[B],
destroy: B => F[Unit]
): Builder[F, A, B] =
apply(a => Resource.make(create(a))(destroy))
private object Defaults {
val defaultReuseState = Reusable.Reuse
val idleTimeAllowedInPool = 30.seconds
def maxPerKey[K](k: K): Int = Function.const(100)(k)
val maxIdle = 100
val maxTotal = 100
def onReaperException[F[_]: Applicative] = { (t: Throwable) =>
Function.const(Applicative[F].unit)(t)
}
}
}
}