Fiber cancellation

UncancelableApp.scala

import cats.effect.{ExitCase, ExitCode, IO, IOApp}
import cats.syntax.flatMap._
import cats.syntax.functor._

import scala.concurrent.duration._

object UncancelableApp extends IOApp {

  override def run(args: List[String]): IO[ExitCode] = {
    val job: IO[String] = for {
      sessionId <- allocateSession.uncancelable
      _ <- verifySession(sessionId).guaranteeCase {
        case ExitCase.Completed => IO.unit
        case ExitCase.Canceled  => terminateSession(sessionId)
        case ExitCase.Error(_)  => terminateSession(sessionId)
      }
    } yield sessionId

    for {
      fiber <- job.start
      _     <- log("Started")
      _     <- fiber.cancel
      _     <- log("Cancelled")
      _     <- IO.sleep(5.seconds)
    } yield ExitCode.Success
  }

  def allocateSession: IO[String] =
    log("Allocating session") >> IO.sleep(3.seconds).as("session_1")

  def verifySession(sessionId: String): IO[Unit] =
    log(s"Verifying session [$sessionId]")

  def terminateSession(sessionId: String): IO[Unit] =
    log(s"Terminating session [$sessionId]")

  def log(message: String): IO[Unit] =
    IO.delay(println(s"${System.currentTimeMillis()} ${Thread.currentThread().getName}: $message"))

}