Zio example of Semaphore usage

output,txt

start 3
start 1
end 1
end 3
start 2
end 2
List(101, 102, 103)

// note, 1st 2 tasks start together because there are 2 permits

Sem1.scala

import zio._
import zio.clock._
import zio.console._
import zio.duration._
import java.util.concurrent.TimeUnit

object Sem1 extends scala.App{

  val runtime = Runtime.default

  val task: Int=> ZIO[Console with Clock, Nothing, Int] = i=> for {
    _ <- putStrLn(s"start $i")
    _ <- ZIO.sleep(Duration(2, TimeUnit.SECONDS))
    _ <- putStrLn(s"end $i")
  } yield i+100

  val semTask: Int=> Semaphore => ZIO[Console with Clock, Nothing, Int] = i=> (sem: Semaphore) => for {
    iplus100 <- sem.withPermit(task(i))
  } yield iplus100

  val semTaskSeq: Semaphore => IndexedSeq[ZIO[Console with Clock, Nothing, Int]] = (sem: Semaphore) => (1 to 3).map(semTask(_)(sem))

  val program = for {

    sem<- Semaphore.make(permits = 2)

    seq <- ZIO.effectTotal(semTaskSeq(sem))

    ipluses: Seq[Int] <- ZIO.collectAllPar(seq)

  } yield ipluses

  val ipluses: Seq[Int] =runtime.unsafeRunTask(program)

  println(ipluses)

}