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package fs2 | |
import cats.implicits._ | |
import cats.effect.{Resource, Sync} | |
import cats.effect.concurrent.Ref | |
import cats.effect.Bracket | |
final class ResourceProxy[F[_], R](state: Ref[F, Option[(R, F[Unit])]])( | |
implicit F: Bracket[F, Throwable] | |
) { | |
def get: F[R] = state.get.flatMap { | |
case None => F.raiseError(new RuntimeException("Cannot get after proxy has been finalized")) | |
case Some((r, _)) => F.pure(r) | |
} | |
// Runs the finalizer for the current proxy target and delays finalizer of newValue until this proxy is finalized | |
def swap(newValue: Resource[F, R]): F[R] = | |
F.uncancelable(newValue.allocated.flatMap { | |
case nv => | |
def doSwap: F[R] = | |
state.access.flatMap { | |
case (current, setter) => | |
current match { | |
case None => | |
nv._2 *> F.raiseError( | |
new RuntimeException("Cannot swap after proxy has been finalized") | |
) | |
case Some((_, oldFinalizer)) => | |
setter(Some(nv)).ifM(oldFinalizer.as(nv._1), doSwap) | |
} | |
} | |
doSwap | |
}) | |
private def runFinalizer: F[Unit] = | |
state.access.flatMap { | |
case (current, setter) => | |
current match { | |
case None => F.raiseError(new RuntimeException("Finalizer already run")) | |
case Some((_, finalizer)) => setter(None).ifM(finalizer, runFinalizer) | |
} | |
} | |
} | |
object ResourceProxy { | |
def apply[F[_]: Sync, R](initialValue: Resource[F, R]): Resource[F, ResourceProxy[F, R]] = { | |
val acquire = for { | |
v <- initialValue.allocated | |
state <- Ref.of[F, Option[(R, F[Unit])]](Some(v)) | |
} yield new ResourceProxy(state) | |
Resource.make(acquire)(_.runFinalizer) | |
} | |
} |
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