bracket and cancel

cancel-after-a-works.txt

starting A
^Cstarting B
stopping B
stopping A

cancel-after-c-doesnt-work.txt

starting A
starting B
starting C
^Cstarting D
doing main work
doing main work
doing main work
doing main work
doing main work
doing main work
stopping D
stopping C
stopping B
stopping A

cancelTask.scala

import cats.implicits._, cats.effect._

object Main extends IOApp {
  def run(args: List[String]): IO[ExitCode] = 
    startAllCancelable(mainWork, List(testStarter("A"), testStarter("B"), testStarter("C"), testStarter("D"))).as(ExitCode.Success)

  def startAllCancelable[A](mainWork: IO[A], taskStarters: List[IO[Fiber[IO, Unit]]]): IO[A] =
    taskStarters.foldRight(mainWork)((t, w) => t.bracket(_ => w)(_.cancel))

  def mainWork: IO[Unit] = 
    IO { println("doing main work"); } *> IO { Thread.sleep(1000) } *> IO { println("doing main work"); } *> IO { Thread.sleep(1000) } *> IO { println("doing main work"); } *> IO { Thread.sleep(1000) } *>
    IO { println("doing main work"); } *> IO { Thread.sleep(1000) } *> IO { println("doing main work"); } *> IO { Thread.sleep(1000) } *> IO { println("doing main work"); } *> IO { Thread.sleep(1000) }

  def testStarter(s: String): IO[Fiber[IO, Unit]] = 
    IO { Thread.sleep(1000) } *> (IO { println("starting " + s) } *> IO.never).void.guarantee(IO { println("stopping " + s) }).start
}