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GenTemporal.scala
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GenTemporal.scala
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/*
* Copyright 2020-2023 Typelevel
*
* 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 cats.effect.kernel
import cats.{Applicative, MonadError, Monoid, Semigroup}
import cats.data._
import cats.effect.kernel.GenTemporal.handleDuration
import cats.syntax.all._
import scala.concurrent.TimeoutException
import scala.concurrent.duration.{Duration, FiniteDuration}
/**
* A typeclass that encodes the notion of suspending fibers for a given duration. Analogous to
* `Thread.sleep` but is only fiber blocking rather than blocking an underlying OS pthread.
*/
trait GenTemporal[F[_], E] extends GenConcurrent[F, E] with Clock[F] {
override def applicative: Applicative[F] = this
/**
* Semantically block the fiber for the specified duration.
*
* @param time
* The duration to semantically block for
*/
def sleep(time: Duration): F[Unit] =
handleDuration[F[Unit]](time, never)(sleep(_))
protected def sleep(time: FiniteDuration): F[Unit]
/**
* Delay the execution of `fa` by a given duration.
*
* @param fa
* The effect to execute
*
* @param time
* The duration to wait before executing fa
*/
def delayBy[A](fa: F[A], time: Duration): F[A] =
handleDuration[F[A]](time, never)(delayBy(fa, _))
protected def delayBy[A](fa: F[A], time: FiniteDuration): F[A] =
productR(sleep(time))(fa)
/**
* Wait for the specified duration after the execution of `fa` before returning the result.
*
* @param fa
* The effect to execute
* @param time
* The duration to wait after executing fa
*/
def andWait[A](fa: F[A], time: Duration): F[A] =
handleDuration(time, productL(fa)(never))(andWait(fa, _))
protected def andWait[A](fa: F[A], time: FiniteDuration): F[A] =
productL(fa)(sleep(time))
/**
* Returns an effect that either completes with the result of the source within the specified
* time `duration` or otherwise evaluates the `fallback`.
*
* The source is canceled in the event that it takes longer than the specified time duration
* to complete. Once the source has been successfully canceled (and has completed its
* finalizers), the fallback will be sequenced. If the source is uncancelable, the resulting
* effect will wait for it to complete before evaluating the fallback.
*
* @param duration
* The time span for which we wait for the source to complete; in the event that the
* specified time has passed without the source completing, the `fallback` gets evaluated
*
* @param fallback
* The task evaluated after the duration has passed and the source canceled
*/
def timeoutTo[A](fa: F[A], duration: Duration, fallback: F[A]): F[A] =
handleDuration(duration, fa)(timeoutTo(fa, _, fallback))
protected def timeoutTo[A](fa: F[A], duration: FiniteDuration, fallback: F[A]): F[A] =
flatMap(race(fa, sleep(duration))) {
case Left(a) => pure(a)
case Right(_) => fallback
}
/**
* Returns an effect that either completes with the result of the source within the specified
* time `duration` or otherwise raises a `TimeoutException`.
*
* The source is canceled in the event that it takes longer than the specified time duration
* to complete. Once the source has been successfully canceled (and has completed its
* finalizers), the `TimeoutException` will be raised. If the source is uncancelable, the
* resulting effect will wait for it to complete before raising the exception.
*
* @param duration
* The time span for which we wait for the source to complete; in the event that the
* specified time has passed without the source completing, a `TimeoutException` is raised
*/
def timeout[A](fa: F[A], duration: Duration)(implicit ev: TimeoutException <:< E): F[A] = {
handleDuration(duration, fa)(timeout(fa, _))
}
protected def timeout[A](fa: F[A], duration: FiniteDuration)(
implicit ev: TimeoutException <:< E): F[A] = {
flatMap(race(fa, sleep(duration))) {
case Left(a) => pure(a)
case Right(_) => raiseError[A](ev(new TimeoutException(duration.toString())))
}
}
/**
* Returns an effect that either completes with the result of the source within the specified
* time `duration` or otherwise raises a `TimeoutException`.
*
* The source is canceled in the event that it takes longer than the specified time duration
* to complete. Unlike
* [[timeout[A](fa:F[A],duration:scala\.concurrent\.duration\.Duration)* timeout]], the
* cancelation of the source will be ''requested'' but not awaited, and the exception will be
* raised immediately upon the completion of the timer. This may more closely match intuitions
* about timeouts, but it also violates backpressure guarantees and intentionally leaks
* fibers.
*
* This combinator should be applied very carefully.
*
* @param duration
* The time span for which we wait for the source to complete; in the event that the
* specified time has passed without the source completing, a `TimeoutException` is raised
* @see
* [[timeout[A](fa:F[A],duration:scala\.concurrent\.duration\.Duration)* timeout]] for a
* variant which respects backpressure and does not leak fibers
*/
def timeoutAndForget[A](fa: F[A], duration: Duration)(
implicit ev: TimeoutException <:< E): F[A] = {
handleDuration(duration, fa)(timeoutAndForget(fa, _))
}
protected def timeoutAndForget[A](fa: F[A], duration: FiniteDuration)(
implicit ev: TimeoutException <:< E): F[A] =
uncancelable { poll =>
implicit val F: GenTemporal[F, E] = this
poll(racePair(fa, sleep(duration))) flatMap {
case Left((oc, f)) =>
poll(f.cancel *> oc.embed(poll(F.canceled) *> F.never))
case Right((f, _)) =>
start(f.cancel) *> raiseError[A](ev(new TimeoutException(duration.toString)))
}
}
/**
* Returns a nested effect which returns the time in a much faster way than
* `Clock[F]#realTime`. This is achieved by caching the real time when the outer effect is run
* and, when the inner effect is run, the offset is used in combination with
* `Clock[F]#monotonic` to give an approximation of the real time. The practical benefit of
* this is a reduction in the number of syscalls, since `realTime` will only be sequenced once
* per `ttl` window, and it tends to be (on most platforms) multiple orders of magnitude
* slower than `monotonic`.
*
* This should generally be used in situations where precise "to the millisecond" alignment to
* the system real clock is not needed. In particular, if the system clock is updated (e.g.
* via an NTP sync), the inner effect will not observe that update until up to `ttl`. This is
* an acceptable tradeoff in most practical scenarios, particularly with frequent sequencing
* of the inner effect.
*
* @param ttl
* The period of time after which the cached real time will be refreshed. Note that it will
* only be refreshed upon execution of the nested effect
*/
def cachedRealTime(ttl: Duration): F[F[FiniteDuration]] = {
implicit val self = this
val cacheValuesF = (realTime, monotonic) mapN {
case (realTimeNow, cacheRefreshTime) => (cacheRefreshTime, realTimeNow - cacheRefreshTime)
}
// Take two measurements and keep the one with the minimum offset. This will no longer be
// required when `IO.unyielding` is merged (see #2633)
val minCacheValuesF = (cacheValuesF, cacheValuesF) mapN {
case (cacheValues1 @ (_, offset1), cacheValues2 @ (_, offset2)) =>
if (offset1 < offset2) cacheValues1 else cacheValues2
}
minCacheValuesF.flatMap(ref).map { cacheValuesRef =>
monotonic.flatMap { timeNow =>
cacheValuesRef.get.flatMap {
case (cacheRefreshTime, offset) =>
if (timeNow >= cacheRefreshTime + ttl)
minCacheValuesF.flatMap {
case cacheValues @ (cacheRefreshTime, offset) =>
cacheValuesRef.set(cacheValues).map(_ => cacheRefreshTime + offset)
}
else
pure(timeNow + offset)
}
}
}
}
}
object GenTemporal {
def apply[F[_], E](implicit F: GenTemporal[F, E]): F.type = F
def apply[F[_]](implicit F: GenTemporal[F, _], d: DummyImplicit): F.type = F
implicit def genTemporalForOptionT[F[_], E](
implicit F0: GenTemporal[F, E]): GenTemporal[OptionT[F, *], E] =
F0 match {
case async: Async[F @unchecked] =>
Async.asyncForOptionT[F](async)
case temporal =>
instantiateGenTemporalForOptionT(temporal)
}
private[kernel] def instantiateGenTemporalForOptionT[F[_], E](
F0: GenTemporal[F, E]): OptionTTemporal[F, E] =
new OptionTTemporal[F, E] {
override implicit protected def F: GenTemporal[F, E] = F0
}
implicit def genTemporalForEitherT[F[_], E0, E](
implicit F0: GenTemporal[F, E]): GenTemporal[EitherT[F, E0, *], E] =
F0 match {
case async: Async[F @unchecked] =>
Async.asyncForEitherT[F, E0](async)
case temporal =>
instantiateGenTemporalForEitherT(temporal)
}
private[kernel] def instantiateGenTemporalForEitherT[F[_], E0, E](
F0: GenTemporal[F, E]): EitherTTemporal[F, E0, E] =
new EitherTTemporal[F, E0, E] {
override implicit protected def F: GenTemporal[F, E] = F0
}
implicit def genTemporalForKleisli[F[_], R, E](
implicit F0: GenTemporal[F, E]): GenTemporal[Kleisli[F, R, *], E] =
F0 match {
case async: Async[F @unchecked] =>
Async.asyncForKleisli[F, R](async)
case temporal =>
instantiateGenTemporalForKleisli(temporal)
}
private[kernel] def instantiateGenTemporalForKleisli[F[_], R, E](
F0: GenTemporal[F, E]): KleisliTemporal[F, R, E] =
new KleisliTemporal[F, R, E] {
override implicit protected def F: GenTemporal[F, E] = F0
}
implicit def genTemporalForIorT[F[_], L, E](
implicit F0: GenTemporal[F, E],
L0: Semigroup[L]): GenTemporal[IorT[F, L, *], E] =
F0 match {
case async: Async[F @unchecked] =>
Async.asyncForIorT[F, L](async, L0)
case temporal =>
instantiateGenTemporalForIorT(temporal)
}
private[kernel] def instantiateGenTemporalForIorT[F[_], L, E](F0: GenTemporal[F, E])(
implicit L0: Semigroup[L]): IorTTemporal[F, L, E] =
new IorTTemporal[F, L, E] {
override implicit protected def F: GenTemporal[F, E] = F0
override implicit protected def L: Semigroup[L] = L0
}
implicit def genTemporalForWriterT[F[_], L, E](
implicit F0: GenTemporal[F, E],
L0: Monoid[L]): GenTemporal[WriterT[F, L, *], E] =
F0 match {
case async: Async[F @unchecked] =>
Async.asyncForWriterT[F, L](async, L0)
case temporal =>
instantiateGenTemporalForWriterT(temporal)
}
private[effect] def handleDuration[A](duration: Duration, ifInf: => A)(
ifFinite: FiniteDuration => A): A =
duration match {
case fd: FiniteDuration => ifFinite(fd)
case Duration.Inf => ifInf
case d =>
throw new IllegalArgumentException(
s"Duration must be either a `FiniteDuration` or `Duration.Inf`, but got: $d")
}
private[kernel] def instantiateGenTemporalForWriterT[F[_], L, E](F0: GenTemporal[F, E])(
implicit L0: Monoid[L]): WriterTTemporal[F, L, E] =
new WriterTTemporal[F, L, E] {
override implicit protected def F: GenTemporal[F, E] = F0
override implicit protected def L: Monoid[L] = L0
}
private[kernel] trait OptionTTemporal[F[_], E]
extends GenTemporal[OptionT[F, *], E]
with GenConcurrent.OptionTGenConcurrent[F, E]
with Clock.OptionTClock[F] {
implicit protected def F: GenTemporal[F, E]
protected def C = F
override protected def delegate: MonadError[OptionT[F, *], E] =
OptionT.catsDataMonadErrorForOptionT[F, E]
def sleep(time: FiniteDuration): OptionT[F, Unit] = OptionT.liftF(F.sleep(time))
}
private[kernel] trait EitherTTemporal[F[_], E0, E]
extends GenTemporal[EitherT[F, E0, *], E]
with GenConcurrent.EitherTGenConcurrent[F, E0, E]
with Clock.EitherTClock[F, E0] {
implicit protected def F: GenTemporal[F, E]
protected def C = F
override protected def delegate: MonadError[EitherT[F, E0, *], E] =
EitherT.catsDataMonadErrorFForEitherT[F, E, E0]
def sleep(time: FiniteDuration): EitherT[F, E0, Unit] = EitherT.liftF(F.sleep(time))
}
private[kernel] trait IorTTemporal[F[_], L, E]
extends GenTemporal[IorT[F, L, *], E]
with GenConcurrent.IorTGenConcurrent[F, L, E]
with Clock.IorTClock[F, L] {
implicit protected def F: GenTemporal[F, E]
protected def C = F
override protected def delegate: MonadError[IorT[F, L, *], E] =
IorT.catsDataMonadErrorFForIorT[F, L, E]
def sleep(time: FiniteDuration): IorT[F, L, Unit] = IorT.liftF(F.sleep(time))
}
private[kernel] trait WriterTTemporal[F[_], L, E]
extends GenTemporal[WriterT[F, L, *], E]
with GenConcurrent.WriterTGenConcurrent[F, L, E]
with Clock.WriterTClock[F, L] {
implicit protected def F: GenTemporal[F, E]
protected def C = F
implicit protected def L: Monoid[L]
override protected def delegate: MonadError[WriterT[F, L, *], E] =
WriterT.catsDataMonadErrorForWriterT[F, L, E]
def sleep(time: FiniteDuration): WriterT[F, L, Unit] = WriterT.liftF(F.sleep(time))
}
private[kernel] trait KleisliTemporal[F[_], R, E]
extends GenTemporal[Kleisli[F, R, *], E]
with GenConcurrent.KleisliGenConcurrent[F, R, E]
with Clock.KleisliClock[F, R] {
implicit protected def F: GenTemporal[F, E]
protected def C = F
override protected def delegate: MonadError[Kleisli[F, R, *], E] =
Kleisli.catsDataMonadErrorForKleisli[F, R, E]
def sleep(time: FiniteDuration): Kleisli[F, R, Unit] = Kleisli.liftF(F.sleep(time))
}
}