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Make PubSubState a trait #972

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a5ad07c
Make `PubSubState` a trait to allow multiple implementations
peterneyens Feb 26, 2025
b57410f
Add sharded `PubSubState` as example of different implementation
peterneyens Feb 26, 2025
a26b978
Keep subscription cleanup in lock
peterneyens Feb 26, 2025
d6ac9ed
Add draft version of Ref based SubscriptionMap
peterneyens Feb 27, 2025
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4 changes: 2 additions & 2 deletions modules/streams/src/main/scala/dev/profunktor/redis4cats/pubsub/PubSub.scala
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Expand Up @@ -56,7 +56,7 @@ object PubSub {
val (acquire, release) = acquireAndRelease[F, K, V](client, codec)
// One exclusive connection for subscriptions and another connection for publishing / stats
for {
state <- Resource.eval(PubSubState.make[F, K, V])
state <- Resource.eval(PubSubState.make[F, K, V](shards = None))
sConn <- Resource.make(acquire)(release)
pConn <- Resource.make(acquire)(release)
} yield new LivePubSubCommands[F, K, V](state, sConn, pConn)
Expand Down Expand Up @@ -84,7 +84,7 @@ object PubSub {
): Resource[F, SubscribeCommands[F, Stream[F, *], K, V]] = {
val (acquire, release) = acquireAndRelease[F, K, V](client, codec)
for {
state <- Resource.eval(PubSubState.make[F, K, V])
state <- Resource.eval(PubSubState.make[F, K, V](shards = None))
conn <- Resource.make(acquire)(release)
} yield new Subscriber(state, conn)
}
Expand Down
215 changes: 204 additions & 11 deletions modules/streams/src/main/scala/dev/profunktor/redis4cats/pubsub/internals/PubSubState.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -16,21 +16,214 @@

package dev.profunktor.redis4cats.pubsub.internals

import cats.{ Applicative, Monad }
import cats.syntax.all._
import cats.effect.kernel.Concurrent
import cats.effect.std.AtomicCell
import cats.effect.kernel.{ Concurrent, Deferred, MonadCancelThrow, Ref, Resource }
import cats.effect.std.{ AtomicCell, MapRef }
import dev.profunktor.redis4cats.data.{ RedisChannel, RedisPattern, RedisPatternEvent }
import fs2.Stream
import fs2.concurrent.Topic

/** We use `AtomicCell` instead of `Ref` because we need locking while side-effecting. */
case class PubSubState[F[_], K, V](
channelSubs: AtomicCell[F, Map[RedisChannel[K], Redis4CatsSubscription[F, V]]],
patternSubs: AtomicCell[F, Map[RedisPattern[K], Redis4CatsSubscription[F, RedisPatternEvent[K, V]]]]
)
object PubSubState {
def make[F[_]: Concurrent, K, V]: F[PubSubState[F, K, V]] =
private[pubsub] trait PubSubState[F[_], K, V] {
def channelSubs: PubSubState.SubscriptionMap[F, RedisChannel[K], V]
def patternSubs: PubSubState.SubscriptionMap[F, RedisPattern[K], RedisPatternEvent[K, V]]
}

private[pubsub] object PubSubState {

trait SubscriptionMap[F[_], K, V] {
def counts: F[Map[K, Long]]

def subscribe(key: K)(create: Resource[F, Topic[F, Option[V]]]): Stream[F, V]

def unsubscribe(key: K): F[Unit]
}

private object SubscriptionMap {
def makeCell[F[_]: Concurrent, K, V]: F[SubscriptionMap[F, K, V]] =
AtomicCell[F].of(Map.empty[K, Redis4CatsSubscription[F, V]]).map(fromCell[F, K, V])

def fromCell[F[_]: MonadCancelThrow, K, V](
cell: AtomicCell[F, Map[K, Redis4CatsSubscription[F, V]]]
): SubscriptionMap[F, K, V] =
new SubscriptionMap[F, K, V] {
override def counts: F[Map[K, Long]] =
cell.get.map(_.iterator.map { case (k, v) => k -> v.subscribers }.toMap)

override def subscribe(key: K)(create: Resource[F, Topic[F, Option[V]]]): Stream[F, V] =
Stream.eval(addSubscription(key)(create)).flatMap(_.stream(remove(key)))

private def addSubscription(key: K)(create: Resource[F, Topic[F, Option[V]]]): F[Redis4CatsSubscription[F, V]] =
cell.evalModify { subscribers =>
val getSubscription = subscribers.get(key) match {
case Some(subscription) =>
// We have an existing subscription, mark that it has one more subscriber.
subscription.addSubscriber.pure[F]
case None =>
// No existing subscription, create a new one.
create.allocated.map { case (topic, cleanup) =>
Redis4CatsSubscription(topic, subscribers = 1, cleanup)
}
}
getSubscription.map(s => (subscribers.updated(key, s), s))
}

private def remove(key: K): F[Unit] =
cell.evalUpdate { subscribers =>
subscribers.get(key) match {
case Some(sub) =>
if (sub.isLastSubscriber) sub.cleanup.as(subscribers - key)
else subscribers.updated(key, sub.removeSubscriber).pure
case None =>
// We were notified about stream termination but we don't have a subscription, this would be a bug
subscribers.pure
}
}

override def unsubscribe(key: K): F[Unit] =
cell.get.map(_.get(key)).flatMap {
// No subscription = nothing to do
case None => Applicative[F].unit
// Publish `None` which will terminate all streams, which will perform cleanup once the last stream
// terminates.
case Some(sub) => sub.topic.publish1(None).void
}
}

def fromShards[F[_]: Monad, K, V](shards: Vector[SubscriptionMap[F, K, V]]): SubscriptionMap[F, K, V] =
new SubscriptionMap[F, K, V] {
override def counts: F[Map[K, Long]] = shards.foldMapM(_.counts)

override def subscribe(key: K)(create: Resource[F, Topic[F, Option[V]]]): Stream[F, V] =
getKeyShard(key).subscribe(key)(create)

override def unsubscribe(key: K): F[Unit] =
getKeyShard(key).unsubscribe(key)

private def getKeyShard(key: K): SubscriptionMap[F, K, V] = {
val location = Math.abs(key.## % shards.size)
shards(location)
}
}

sealed trait SubscriptionState[F[_], V]
object SubscriptionState {
final case class Active[F[_], V](subscription: Redis4CatsSubscription[F, V]) extends SubscriptionState[F, V]
final case class Starting[F[_], V](done: F[Unit]) extends SubscriptionState[F, V]
final case class ShuttingDown[F[_], V](done: F[Unit]) extends SubscriptionState[F, V]
}

def makeRef[F[_]: Concurrent, K, V]: F[SubscriptionMap[F, K, V]] =
Ref[F].of(Map.empty[K, SubscriptionState[F, V]]).map(fromRef[F, K, V])

def fromRef[F[_]: Concurrent, K, V](
ref: Ref[F, Map[K, SubscriptionState[F, V]]]
): SubscriptionMap[F, K, V] =
new SubscriptionMap[F, K, V] {
import SubscriptionState._

private val mapRef = MapRef.fromSingleImmutableMapRef(ref)

override def counts: F[Map[K, Long]] =
ref.get.map(_.iterator.collect { case (k, Active(v)) => k -> v.subscribers }.toMap)

override def subscribe(key: K)(create: Resource[F, Topic[F, Option[V]]]): Stream[F, V] =
Stream.eval(addSubscription(key)(create)).flatMap(_.stream(remove(key)))

private def addSubscription(key: K)(create: Resource[F, Topic[F, Option[V]]]): F[Redis4CatsSubscription[F, V]] =
Deferred[F, Unit].flatMap { d =>
ref.flatModify[Redis4CatsSubscription[F, V]] { subscribers =>
subscribers.get(key) match {
case Some(Active(subscription)) =>
// We have an existing subscription, mark that it has one more subscriber.
val newSubscription = subscription.addSubscriber
(subscribers.updated(key, Active(newSubscription)), newSubscription.pure[F])
case Some(ShuttingDown(wait)) =>
// an existing subscription is getting shut down, wait and try again
(subscribers, wait >> addSubscription(key)(create))
case Some(Starting(wait)) =>
// an existing subscription is getting created, wait and try again
(subscribers, wait >> addSubscription(key)(create))
case None =>
// No existing subscription, create a new one.
val start = create.allocated.flatMap { case (topic, cleanup) =>
val subscription = Redis4CatsSubscription(topic, subscribers = 1, cleanup)
mapRef(key).flatModify {
case Some(Starting(_)) => (Some(Active(subscription)), d.complete(()).as(subscription))
case _ =>
// this would be a bug, we only expect a starting subscription
// TODO should we error?
(None, cleanup >> d.complete(()) >> addSubscription(key)(create))
}
}
(subscribers.updated(key, Starting(d.get)), start)
}
}
}

private def remove(key: K): F[Unit] =
Deferred[F, Unit].flatMap { d =>
mapRef(key).flatModify {
case Some(Active(sub)) =>
if (sub.isLastSubscriber) {
val cleanup = sub.cleanup >> mapRef(key).flatModify {
case Some(ShuttingDown(_)) => (None, d.complete(()).void)
case _ => (None, Applicative[F].unit) // TODO bug
}
(Some(ShuttingDown(d.get)), cleanup)
} else (Some(Active(sub.removeSubscriber)), Applicative[F].unit)
case other => // bug
(other, Applicative[F].unit)
}
}

override def unsubscribe(key: K): F[Unit] =
ref.get.map(_.get(key)).flatMap {
// No subscription = nothing to do
case None => Applicative[F].unit
// Subscription already shutting down = nothing to do
case Some(ShuttingDown(_)) => Applicative[F].unit
// Publish `None` which will terminate all streams, which will perform cleanup once the last stream
// terminates.
case Some(Active(sub)) => sub.topic.publish1(None).void
// wait until the subscription has started and unsubscribe
case Some(Starting(wait)) => wait >> unsubscribe(key)
}
}
}

def make[F[_]: Concurrent, K, V](shards: Option[Int]): F[PubSubState[F, K, V]] =
shards.filter(_ > 1) match {
case None => singleRef[F, K, V]
case Some(n) => sharded[F, K, V](n)
}

def single[F[_]: Concurrent, K, V]: F[PubSubState[F, K, V]] =
for {
channelSubs0 <- SubscriptionMap.makeCell[F, RedisChannel[K], V]
patternSubs0 <- SubscriptionMap.makeCell[F, RedisPattern[K], RedisPatternEvent[K, V]]
} yield new PubSubStateImpl[F, K, V](channelSubs0, patternSubs0)

private def sharded[F[_]: Concurrent, K, V](number: Int): F[PubSubState[F, K, V]] = {
assert(number > 1)
for {
channelShards <- SubscriptionMap.makeCell[F, RedisChannel[K], V].replicateA(number)
patternShards <- SubscriptionMap.makeCell[F, RedisPattern[K], RedisPatternEvent[K, V]].replicateA(number)
} yield new PubSubStateImpl[F, K, V](
SubscriptionMap.fromShards(channelShards.toVector),
SubscriptionMap.fromShards(patternShards.toVector)
)
}

private def singleRef[F[_]: Concurrent, K, V]: F[PubSubState[F, K, V]] =
for {
channelSubs <- AtomicCell[F].of(Map.empty[RedisChannel[K], Redis4CatsSubscription[F, V]])
patternSubs <- AtomicCell[F].of(Map.empty[RedisPattern[K], Redis4CatsSubscription[F, RedisPatternEvent[K, V]]])
} yield apply(channelSubs, patternSubs)
channelSubs0 <- SubscriptionMap.makeRef[F, RedisChannel[K], V]
patternSubs0 <- SubscriptionMap.makeRef[F, RedisPattern[K], RedisPatternEvent[K, V]]
} yield new PubSubStateImpl[F, K, V](channelSubs0, patternSubs0)

private class PubSubStateImpl[F[_], K, V](
override val channelSubs: PubSubState.SubscriptionMap[F, RedisChannel[K], V],
override val patternSubs: PubSubState.SubscriptionMap[F, RedisPattern[K], RedisPatternEvent[K, V]]
) extends PubSubState[F, K, V]
}
109 changes: 21 additions & 88 deletions modules/streams/src/main/scala/dev/profunktor/redis4cats/pubsub/internals/Subscriber.scala
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Expand Up @@ -18,10 +18,8 @@ package dev.profunktor.redis4cats
package pubsub
package internals

import cats.Applicative
import cats.effect.kernel._
import cats.effect.kernel.implicits._
import cats.effect.std.{ AtomicCell, Dispatcher }
import cats.effect.std.Dispatcher
import cats.syntax.all._
import dev.profunktor.redis4cats.data.{ RedisChannel, RedisPattern, RedisPatternEvent }
import dev.profunktor.redis4cats.effect.{ FutureLift, Log }
Expand Down Expand Up @@ -66,103 +64,38 @@ private[pubsub] class Subscriber[F[_]: Async: FutureLift: Log, K, V](
Subscriber.unsubscribeFrom(pattern, state.patternSubs)

override def internalChannelSubscriptions: F[Map[RedisChannel[K], Long]] =
state.channelSubs.get.map(_.iterator.map { case (k, v) => k -> v.subscribers }.toMap)
state.channelSubs.counts

override def internalPatternSubscriptions: F[Map[RedisPattern[K], Long]] =
state.patternSubs.get.map(_.iterator.map { case (k, v) => k -> v.subscribers }.toMap)
state.patternSubs.counts
}
object Subscriber {

/** Check if we have a subscriber for this channel and remove it if we do.
*
* If it is the last subscriber, perform the subscription cleanup.
*/
private def onStreamTermination[F[_]: Applicative: Log, K, V](
subs: AtomicCell[F, Map[K, Redis4CatsSubscription[F, V]]],
key: K
): F[Unit] = subs.evalUpdate { subscribers =>
subscribers.get(key) match {
case None =>
Log[F]
.error(
s"We were notified about stream termination for $key but we don't have a subscription, " +
s"this is a bug in redis4cats!"
)
.as(subscribers)
case Some(sub) =>
if (!sub.isLastSubscriber) subscribers.updated(key, sub.removeSubscriber).pure
else sub.cleanup.as(subscribers - key)
}
}

private def unsubscribeFrom[F[_]: MonadCancelThrow: Log, K, V](
private def unsubscribeFrom[F[_], K, V](
key: K,
subs: AtomicCell[F, Map[K, Redis4CatsSubscription[F, V]]]
state: PubSubState.SubscriptionMap[F, K, V]
): F[Unit] =
subs.evalUpdate { subscribers =>
subscribers.get(key) match {
case None =>
// No subscription = nothing to do
Log[F]
.debug(s"Not unsubscribing from $key because we don't have a subscription")
.as(subscribers)
case Some(sub) =>
// Publish `None` which will terminate all streams, which will perform cleanup once the last stream
// terminates.
(Log[F].info(
s"Unsubscribing from $key with ${sub.subscribers} subscribers"
) *> sub.topic.publish1(None)).uncancelable.as(subscribers)
}
}
state.unsubscribe(key)

private def subscribe[F[_]: Async: Log, TypedKey, SubValue, K, V](
key: TypedKey,
subs: AtomicCell[F, Map[TypedKey, Redis4CatsSubscription[F, SubValue]]],
state: PubSubState.SubscriptionMap[F, TypedKey, SubValue],
subConnection: StatefulRedisPubSubConnection[K, V],
subscribeToRedis: F[Unit],
unsubscribeFromRedis: F[Unit]
)(makeListener: (Dispatcher[F], Topic[F, Option[SubValue]]) => RedisPubSubListener[K, V]): Stream[F, SubValue] =
Stream
.eval(subs.evalModify { subscribers =>
def stream(sub: Redis4CatsSubscription[F, SubValue]) =
sub.stream(onStreamTermination(subs, key))

subscribers.get(key) match {
case Some(subscription) =>
// We have an existing subscription, mark that it has one more subscriber.
val newSubscription = subscription.addSubscriber
val newSubscribers = subscribers.updated(key, newSubscription)
Log[F]
.debug(
s"Returning existing subscription for $key, " +
s"subscribers: ${subscription.subscribers} -> ${newSubscription.subscribers}"
)
.as((newSubscribers, stream(newSubscription)))

case None =>
// No existing subscription, create a new one.
val makeSubscription = for {
_ <- Log[F].info(s"Creating subscription for $key")
// We use parallel dispatcher because multiple subscribers can be interested in the same key
dispatcherTpl <- Dispatcher.parallel[F].allocated
(dispatcher, cleanupDispatcher) = dispatcherTpl
topic <- Topic[F, Option[SubValue]]
listener = makeListener(dispatcher, topic)
cleanupListener = Sync[F].delay(subConnection.removeListener(listener))
cleanup = (
Log[F].debug(s"Cleaning up resources for $key subscription") *>
unsubscribeFromRedis *> cleanupListener *> cleanupDispatcher *>
Log[F].debug(s"Cleaned up resources for $key subscription")
).uncancelable
_ <- Sync[F].delay(subConnection.addListener(listener))
_ <- subscribeToRedis
sub = Redis4CatsSubscription(topic, subscribers = 1, cleanup)
newSubscribers = subscribers.updated(key, sub)
_ <- Log[F].debug(s"Created subscription for $key")
} yield (newSubscribers, stream(sub))

makeSubscription.uncancelable
}
})
.flatten
state.subscribe(key) {
for {
_ <- Resource.eval(Log[F].info(s"Creating subscription for $key"))
// We use parallel dispatcher because multiple subscribers can be interested in the same key
dispatcher <- Dispatcher.parallel[F]
topic <- Resource.eval(Topic[F, Option[SubValue]])
_ <- Resource.make {
val listener = makeListener(dispatcher, topic)
Sync[F].delay(subConnection.addListener(listener)).as(listener)
}(listener => Sync[F].delay(subConnection.removeListener(listener)))
_ <- Resource.make(subscribeToRedis)(_ => unsubscribeFromRedis)
_ <- Resource.eval(Log[F].debug(s"Created subscription for $key"))
} yield topic
}
}