Observe a rate limit when interacting with an expensive resource

RateLimitObserving.kt

import kotlinx.coroutines.*
import kotlin.random.Random

fun main() = runBlocking {
    val start = System.nanoTime()
    val result = observeRateLimitAsync(1000) {
        someExpensiveOperationWithRateLimit()
    }.await()
    println("Result [$result] retrieved in ${(System.nanoTime() - start) / 1_000_000} ms")
}

private fun someExpensiveOperationWithRateLimit(): Int {
    runBlocking { delay(5000) }
    return Random.nextInt(0, 100)
}

private suspend fun <T> observeRateLimitAsync(onePerMillis: Long, block: () -> T): Deferred<T> = withContext(Dispatchers.Default) {
    launch {
        delay(onePerMillis)
        println("Rate limit observed: 1 request per $onePerMillis ms")
    }

    async {
        block()
    }
}