parallel-fs2.scala

import java.util.concurrent.atomic.AtomicInteger
import cats._
import cats.effect._
import cats.effect.implicits._

object foo extends IOApp {
  import fs2._

  val ai = new AtomicInteger()
  override def run(args: List[String]): IO[ExitCode] =
    Stream(1, 2, 3, 4, 5, 6)
      .broadcast[IO]
      .parEvalMap(4) { s =>
        val index = ai.getAndIncrement()
        s.evalMap(x => IO(Console.println(s"$index $x"))).compile.drain
      }
      .compile
      .drain
      .redeem(_ => ExitCode.Error, _ => ExitCode.Success)

}