ProducerConsumerWithStdQueue.scala

//> using scala "2.13.11"
//> using lib "org.typelevel::cats-effect::3.5.1"

import cats.effect._
import cats.effect.std.{Console, Queue}
import cats.instances.list._
import cats.syntax.all._

object ProducerConsumerWithStdQueue extends IOApp {

  def producer(id: Int, q: Queue[IO, Int], counterR: Ref[IO, Int]): IO[Unit] =
    for {
      i <- counterR.getAndUpdate(_ + 1)
      _ <- q.offer(i)
      _ <- if (i % 10000 == 0) IO.println(s"Producer $id has reached $i items") else IO.unit
      _ <- producer(id, q, counterR)
    } yield ()

  def consumer(id: Int, q: Queue[IO, Int]): IO[Unit] =
    for {
      i <- q.take
      _ <- if (i % 10000 == 0) IO.println(s"Consumer $id has reached $i items") else IO.unit
      _ <- consumer(id, q)
    } yield ()

  override def run(args: List[String]): IO[ExitCode] =
    for {
      counterR <- Ref.of[IO, Int](0)
      q <- Queue.unbounded[IO, Int]
      producers = List.range(1, 11).map(producer(_, q, counterR)) // 10 producers
      consumers = List.range(1, 11).map(consumer(_, q)) // 10 consumers
      res <- (producers ++ consumers)
        .parSequence.as(ExitCode.Success)
        .handleErrorWith { t =>
          Console[IO].errorln(s"Error caught: ${t.getMessage}").as(ExitCode.Error)
        }
    } yield res
}