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Split out channel resource management into a generic Coldswap (close #20
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107
...es/core/src/main/scala/com.snowplowanalytics.snowplow.snowflake/processing/Coldswap.scala
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| /* | ||
| * Copyright (c) 2014-present Snowplow Analytics Ltd. All rights reserved. | ||
| * | ||
| * This software is made available by Snowplow Analytics, Ltd., | ||
| * under the terms of the Snowplow Limited Use License Agreement, Version 1.0 | ||
| * located at https://docs.snowplow.io/limited-use-license-1.0 | ||
| * BY INSTALLING, DOWNLOADING, ACCESSING, USING OR DISTRIBUTING ANY PORTION | ||
| * OF THE SOFTWARE, YOU AGREE TO THE TERMS OF SUCH LICENSE AGREEMENT. | ||
| */ | ||
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| package com.snowplowanalytics.snowplow.snowflake.processing | ||
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| import cats.effect.{Async, Ref, Resource, Sync} | ||
| import cats.effect.std.Semaphore | ||
| import cats.Functor | ||
| import cats.implicits._ | ||
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| /** | ||
| * Manages swapping of Resources | ||
| * | ||
| * Inspired by `cats.effect.std.Hotswap` but with differences. A Hotswap is "hot" because a `swap` | ||
| * acquires the next resource before closing the previous one. Whereas this Coldswap is "cold" | ||
| * because it always closes any previous Resources before acquiring the next one. | ||
| * | ||
| * * '''Note''': The resource cannot be simultaneously open and closed, and so | ||
| * `coldswap.opened.surround(coldswap.closed.use_)` will deadlock. | ||
| */ | ||
| final class Coldswap[F[_]: Sync, A] private ( | ||
| sem: Semaphore[F], | ||
| ref: Ref[F, Coldswap.State[F, A]], | ||
| resource: Resource[F, A] | ||
| ) { | ||
| import Coldswap._ | ||
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| /** | ||
| * Gets the current resource, or opens a new one if required. The returned `A` is guaranteed to be | ||
| * available for the duration of the `Resource.use` block. | ||
| */ | ||
| def opened: Resource[F, A] = | ||
| (sem.permit *> Resource.eval[F, State[F, A]](ref.get)).flatMap { | ||
| case Opened(a, _) => Resource.pure(a) | ||
| case Closed => | ||
| for { | ||
| _ <- releaseHeldPermit(sem) | ||
| _ <- acquireAllPermits(sem) | ||
| a <- Resource.eval(doOpen(ref, resource)) | ||
| } yield a | ||
| } | ||
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| /** | ||
| * Closes the resource if it was open. The resource is guaranteed to remain closed for the | ||
| * duration of the `Resource.use` block. | ||
| */ | ||
| def closed: Resource[F, Unit] = | ||
| (sem.permit *> Resource.eval(ref.get)).flatMap { | ||
| case Closed => Resource.unit | ||
| case Opened(_, _) => | ||
| for { | ||
| _ <- releaseHeldPermit(sem) | ||
| _ <- acquireAllPermits(sem) | ||
| _ <- Resource.eval(doClose(ref)) | ||
| } yield () | ||
| } | ||
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| } | ||
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| object Coldswap { | ||
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| private sealed trait State[+F[_], +A] | ||
| private case object Closed extends State[Nothing, Nothing] | ||
| private case class Opened[F[_], A](value: A, close: F[Unit]) extends State[F, A] | ||
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| def make[F[_]: Async, A](resource: Resource[F, A]): Resource[F, Coldswap[F, A]] = | ||
| for { | ||
| sem <- Resource.eval(Semaphore[F](Long.MaxValue)) | ||
| ref <- Resource.eval(Ref.of[F, State[F, A]](Closed)) | ||
| _ <- Resource.onFinalize(acquireAllPermits(sem).use(_ => doClose(ref))) | ||
| } yield new Coldswap(sem, ref, resource) | ||
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| private def releaseHeldPermit[F[_]: Functor](sem: Semaphore[F]): Resource[F, Unit] = | ||
| Resource.makeFull[F, Unit](poll => poll(sem.release))(_ => sem.acquire) | ||
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| private def acquireAllPermits[F[_]: Functor](sem: Semaphore[F]): Resource[F, Unit] = | ||
| Resource.makeFull[F, Unit](poll => poll(sem.acquireN(Long.MaxValue)))(_ => sem.releaseN(Long.MaxValue)) | ||
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| private def doClose[F[_]: Sync, A](ref: Ref[F, State[F, A]]): F[Unit] = | ||
| ref.get.flatMap { | ||
| case Closed => Sync[F].unit | ||
| case Opened(_, close) => | ||
| Sync[F].uncancelable { _ => | ||
| close *> ref.set(Closed) | ||
| } | ||
| } | ||
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| private def doOpen[F[_]: Sync, A](ref: Ref[F, State[F, A]], resource: Resource[F, A]): F[A] = | ||
| ref.get.flatMap { | ||
| case Opened(a, _) => Sync[F].pure(a) | ||
| case Closed => | ||
| Sync[F].uncancelable { _ => | ||
| for { | ||
| (a, close) <- resource.allocated | ||
| _ <- ref.set(Opened(a, close)) | ||
| } yield a | ||
| } | ||
| } | ||
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| } |
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