Sleep

You can configure how the delays between retries are implemented.

This is done using the Sleep type class:

trait Sleep[M[_]] {

  def sleep(delay: FiniteDuration): M[Unit]

}

Out of the box, the core module provides instances for any type with an implicit cats-effect Temporal in scope.

For example using cats.effect.IO:

import retry.Sleep
import cats.effect.IO
import scala.concurrent.duration._
import cats.effect.unsafe.implicits.global

Sleep[IO].sleep(10.milliseconds)

Or if you’re using an abstract F[_]:

import retry.Sleep
import cats.effect.Temporal
import scala.concurrent.duration._

def sleepWell[F[_]: Temporal] =
  Sleep[F].sleep(10.milliseconds)

Being able to inject your own Sleep instance can be handy in tests, as you can mock it out to avoid slowing down your unit tests.

alleycats-retry

The alleycats-retry module provides instances for cats.Id, cats.Eval and Future that simply do a Thread.sleep(...).

You can add it to your build.sbt as follows:

libraryDependencies += "com.github.cb372" %% "alleycats-retry" % "3.1.0"

To use them, simply import retry.alleycats.instances._:

import retry.Sleep
import retry.alleycats.instances._
import scala.concurrent.Future
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits.global

Sleep[Future].sleep(10.milliseconds)

import retry.Sleep
import retry.alleycats.instances._
import cats.Id
import scala.concurrent.duration._

Sleep[Id].sleep(10.milliseconds)

Note: these instances are not provided if you are using Scala.js, as Thread.sleep doesn’t make any sense in JavaScript.