val a = IO.effectAsync[Any, Nothing, Unit] { cb =>
  ec3.submit(new Runnable {
    override def run(): Unit = {
      println(Thread.currentThread().getName + " (async)")
      cb(UIO.unit)
    }
  })
}

run("async") {
  printThread *> a *> printThread
}

/*
Outputs:

-- async --
main
ec3-1-1627960023 (async)
zio-default-async-7-1702146597
*/