Semaphore Fun

Example.scala

import zio.*
import zio.Executor
import zio.Console.printLine

object CustomizedRuntimeZIOApp extends ZIOAppDefault:
  val blockingTask = (n: Int) =>
    for {
      _ <- printLine(s"start potentially long API call or something for $n")
      r <- Random.nextIntBetween(500, 1000)
      _ <- ZIO.succeed(Thread.sleep(r))
      _ <- printLine(s"end duration: $r for $n")
    } yield n

  val semTask = (n: Int, sem: Semaphore) =>
    for {
      n <- sem
        .withPermit(blockingTask(n).debug(Thread.currentThread().getName))
    } yield n

  val semTaskSeq = (sem: Semaphore) => (1 to 1000000).map(n => semTask(n, sem))

  val program = for {

    sem <- Semaphore.make(permits = 5)

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

    _ <- ZIO.collectAllPar(seq)

  } yield ()

  def run = program