CatsCountDownLatch.scala

import cats.effect.Concurrent
import cats.syntax.flatMap._
import cats.syntax.functor._
import cats.effect.concurrent.Semaphore

trait CountDownLatch[F[_]] {
  def countDown: F[Unit]
  def await: F[Unit]
}

object CountDownLatch {

  def apply[F[_]: Concurrent](count: Int): F[CountDownLatch[F]] =
    for {
      sem <- Semaphore[F](0)
      get <- Concurrent.memoize(sem.acquireN(count.toLong))
    } yield new CountDownLatch[F] {
      override val countDown: F[Unit] = sem.release
      override val await: F[Unit] = get
    }
}