Kotlin Coroutines PoC of Go's singleflight

Singleflight.kt

import kotlinx.coroutines.*

private val deferreds = mutableMapOf<String, Deferred<*>>()

@Suppress("UNCHECKED_CAST")
fun <T> doAsync(key: String, action: suspend () -> T): Deferred<T> {
    val deferredResult = deferreds[key]?.takeIf { it.isActive }
            ?: GlobalScope.async { action() }.also { deferreds[key] = it }
    return deferredResult as Deferred<T>
}

fun forget(key: String) {
    deferreds[key]?.cancel()
}

Test.kt

import kotlinx.coroutines.*

suspend fun main() = coroutineScope {
    val result1 = doAsync("delay") {
        delay(500L)
        println("Do only once")
        1
    }

    val result2 = doAsync("delay") {
        delay(500L)
        println("Do only once")
        2
    }
    result1.await()
    val result3 = doAsync("delay") {
        delay(500L)
        println("Do once more")
        3
    }
    println("result1: ${result1.await()}, result2: ${result2.await()}, result3: ${result3.await()}")
}