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StreamSupervisor.scala
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StreamSupervisor.scala
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/*
* Copyright 2023 Valdemar Grange
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package gql.interpreter
import cats.data._
import cats.effect._
import cats.implicits._
import cats.effect.std._
import fs2.{Chunk, Stream}
trait StreamSupervisor[F[_]] {
def acquireAwait[A](stream: Stream[F, A]): F[(StreamToken, Either[Throwable, A])]
def release(token: Set[StreamToken]): F[Unit]
def freeUnused(token: StreamToken, resource: ResourceToken): F[Unit]
def changes: Stream[F, NonEmptyList[(StreamToken, ResourceToken, Either[Throwable, ?])]]
}
object StreamSupervisor {
final case class State[F[_]](
unsubscribe: F[Unit],
allocatedResources: Vector[(ResourceToken, F[Unit])]
)
def apply[F[_]](openTail: Boolean)(implicit F: Async[F]): Stream[F, StreamSupervisor[F]] = {
def removeStates(xs: List[State[F]]) = {
xs.traverse_(_.unsubscribe) >>
xs.traverse_(_.allocatedResources.toList.traverse_ { case (_, fa) => fa })
}
type StateMap = Map[StreamToken, State[F]]
fs2.Stream.resource(Supervisor[F]).flatMap { sup =>
fs2.Stream
.bracket(F.ref(Map.empty[StreamToken, State[F]]))(_.get.flatMap(xs => removeStates(xs.values.toList)))
.flatMap { (state: Ref[F, StateMap]) =>
fs2.Stream.eval(Queue.bounded[F, Chunk[(StreamToken, ResourceToken, Either[Throwable, ?])]](1024)).map { q =>
new StreamSupervisor[F] {
override def acquireAwait[A](stream: Stream[F, A]): F[(Unique.Token, Either[Throwable, A])] =
F.uncancelable { _ =>
for {
token <- F.unique
head <- F.deferred[Either[Throwable, A]]
start <- F.deferred[Unit]
// close <- {
// def go(stream: fs2.Stream[F, (Either[Throwable, A], Long)]): fs2.Pull[F, Nothing, Unit] =
// stream.pull.uncons1
// .flatMap {
// case None => fs2.Pull.done
// case Some(((hd, i), tl)) =>
// fs2.Pull.eval(F.deferred[Either[Throwable, Unit]]).flatMap { die =>
// fs2.Pull
// .extendScopeTo(fs2.Stream.never[F].interruptWhen(die))
// .evalMap(back => sup.supervise(back.compile.drain))
// .flatMap { resourceFiber =>
// fs2.Pull.eval(F.unique).flatMap { resourceToken =>
// val updateStateF = state.modify { m =>
// m.get(token) match {
// // We are closed for business
// case None => (m, resourceFiber.cancel)
// case Some(state) =>
// val resourceEntry = (resourceToken, resourceFiber.cancel)
// val newEntry = state.copy(
// allocatedResources = state.allocatedResources :+ resourceEntry
// )
// val publish =
// if (i == 0) head.complete(hd).void
// else if (openTail) q.offer(Chunk((token, resourceToken, hd)))
// else F.unit
// (m + (token -> newEntry), publish)
// }
// }.flatten
// fs2.Pull.eval(updateStateF) >> go(tl)
// }
// }
// }
// }
// sup.supervise {
// start.get >> go(stream.attempt.zipWithIndex).stream.as(()).compile.drain
// }
// }.map(_.cancel)
// TODO find a more elegant way of holding fs2 Leases
// start <- F.deferred[Unit]
// Hold fs2 leases by:
// 1. allocate a token for the resource and a killSignal / releaseSignal
// 2. do data publishing
// 3. await one killSignal for every stream element/resource scope
close <- sup
.supervise {
{
fs2.Stream.eval(start.get) >> {
stream.attempt.zipWithIndex
.evalMap { case (a, i) =>
F.deferred[Unit].flatMap { killSignal =>
F.unique.flatMap { resourceToken =>
state.update { m =>
m.get(token) match {
// We are closed for business
case None => m
case Some(state) =>
val resourceEntry = (resourceToken, killSignal.complete(()).void)
val newEntry = state.copy(
allocatedResources = state.allocatedResources :+ resourceEntry
)
(m + (token -> newEntry))
}
} >> {
if (i == 0) head.complete(a).void
else if (openTail) q.offer(Chunk((token, resourceToken, a)))
else F.unit
} as killSignal.get
}
}
}
.map(fs2.Stream.eval(_))
.parJoinUnbounded
}
}.compile.drain
}
.map(_.cancel)
_ <- state.update(_ + (token -> State(close, Vector.empty)))
_ <- start.complete(())
} yield head.get tupleLeft token
}.flatten
override def release(tokens: Set[StreamToken]): F[Unit] =
F.uncancelable { _ =>
state
.modify(m => (m -- tokens, tokens.toList.flatMap(m.get(_).toList)))
.flatMap(removeStates)
}
override def freeUnused(token: StreamToken, resource: ResourceToken): F[Unit] =
F.uncancelable { _ =>
state.modify { s =>
s.get(token) match {
case None => (s, F.unit)
case Some(state) =>
val (release, keep) = state.allocatedResources.span { case (k, _) => k != resource }
val newState = state.copy(allocatedResources = keep)
(s + (token -> newState), release.traverse_ { case (_, fa) => fa })
}
}.flatten
}
override def changes: Stream[F, NonEmptyList[(StreamToken, ResourceToken, Either[Throwable, ?])]] =
Stream
.fromQueueUnterminatedChunk(q)
.chunks
.map(_.toNel)
.unNone
}
}
}
}
}
}