DispatchersDefault1.kt

fun main() {
    println("Start")
    val activity = Activity()
    activity.doLotOfThings()
    Thread.sleep(2000)
    activity.destroy()
    println("Done")
}

class Activity : CoroutineScope by CoroutineScope(Dispatchers.Default) {

    fun doLotOfThings() {
        launch {
            repeat(1_000) {
                delay(400)
                doThing()
            }
        }
    }

    private fun doThing() {
        println("[${Thread.currentThread().name}] doing something...")
    }

    fun destroy() {
        cancel()
    }
}