Convert guava ListenableFuture to cats-effect

[Daenyth]

Pulled this from discord after needing it for a second time
Edit: I made it into a jar!
https://daenyth.github.io/cats-effect-guava/

[armanbilge]

Seems like it should be possible to add cancellation, like this?

cats-effect/kernel/jvm/src/main/scala/cats/effect/kernel/AsyncPlatform.scala

Line 45 in 60cc217

Some(void(delay(cf.cancel(false))))

[Daenyth]

Would that be back.as(Some(..)) ?

[armanbilge]

I think you may need to restructure your snippet to get the EC/future outside of the async. There's some trickyness, see #2665.

[Daenyth]

Got it -

def fromListenableFuture[F[_]: Async, A](lfF: F[ListenableFuture[A]]): F[A] =
  Async[F].async { cb =>
    Async[F].executionContext.flatMap { ec =>
      lfF.flatMap { lf =>
        Sync[F].delay {
          lf.addListener(
            () =>
              cb(
                try Right(lf.get)
                catch {
                  case ee: ExecutionException if ee.getCause != null =>
                    Left(ee.getCause)
                  case NonFatal(e) => Left(e)
                }
              ),
            (command: Runnable) => ec.execute(command)
          )

          Some(Sync[F].delay(lf.cancel(false)).void)
        }
      }
    }
  }

And unit tests:

import cats.effect.IO
import com.google.common.util.concurrent.MoreExecutors

import java.util.concurrent.{CancellationException, Executors}
import scala.concurrent.duration._
import scala.util.control.NoStackTrace

class GuavaSpec extends munit.CatsEffectSuite {

  private val lfService =
    MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(1))

  test("fromListenableFuture signals success") {

    def lf() = lfService.submit(() => true)

    println(lf())
    fromListenableFuture(IO(lf())).assert
  }

  test("fromListenableFuture signals thrown failures") {
    case object TestException extends Exception with NoStackTrace
    def lf() = lfService.submit[Unit](() => throw TestException)
    fromListenableFuture(IO(lf())).intercept[TestException.type]
  }

  // Styled after https://github.com/typelevel/cats-effect/pull/2665/files#diff-d68e0c39ae977e5c8643174d66c7659ebfb6bc5f3f6e19a581b7aefbfc6024bd
  test("fromListenableFuture signals cancellation") {

    val smallDelay: IO[Unit] = IO.sleep(100.millis)

    lazy val lf = lfService.submit[Unit](() => Thread.sleep(200))

    val test = for {

      fiber <- fromListenableFuture(IO(lf)).start
      _ <- smallDelay // time for the callback to be set up
      _ <- fiber.cancel
      _ <- IO(lf.get()).intercept[CancellationException]
    } yield true

    test.assert
  }

}

[armanbilge]

Nice! This definitely deserves more than a gist 😝