Kotlin Coroutines, a deeper look

Main.kt

// Inspired by http://akarnokd.blogspot.ru/2017/09/rxjava-vs-kotlin-coroutines-quick-look.html
// Requires Kotlin 1.2.30 or later
// Uses kotlinx.coroutines library

import kotlinx.coroutines.experimental.*
import kotlin.system.*

suspend fun f1(i: Int): Int {
    println("f1 attempt $i")
    delay(if (i != 3) 2000 else 200)
    return 1
}

suspend fun f2(i: Int): Int {
    println("f2 attempt $i")
    delay(if (i != 3) 2000 else 200)
    return 2
}

suspend fun <T> retry(block: suspend (Int) -> T): T {
    for (i in 1..5) { // try 5 times
        try {
            return withTimeout(500) { // with timeout
                block(i)
            }
        } catch (e: TimeoutCancellationException) { /* retry */ }
    }
    return block(0) // last time just invoke without timeout
}

fun main(args: Array<String>) = runBlocking {
    val time = measureTimeMillis {
        val v1 = async { retry { f1(it) } }
        val v2 = async { retry { f2(it) } }
        println("Result = ${v1.await() + v2.await()}")
    }
    println("Completed in $time ms")
}