Is there a better way to keep parallelism in the `...

# coroutines

[Nino]

Is there a better way to keep parallelism in the initializeStuffAndGetFoo() function between my coroutines without this dangerous first() as String ?

https://pl.kotl.in/7fVqO3EXP

import kotlinx.coroutines.*

fun main() = runBlocking {
    println(initializeStuffAndGetFoo())
}

suspend fun initializeStuffAndGetFoo() = withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
    listOf(
        async { getFooValue() },
        async { initA() },
        async { initB() },
    ).awaitAll().first() as String
}

suspend fun getFooValue(): String {
    delay(2_000)
    return "Foo"
}

suspend fun initA() = delay(1_000)
suspend fun initB() = delay(3_000)

[Nino]

I forgot that async starts eagerly by default so we can use something like that, can't we ?

import kotlinx.coroutines.*

fun main() = runBlocking {
    println(initializeStuffAndGetFoo())
}

suspend fun initializeStuffAndGetFoo() = withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
    val fooAsync = async { getFooValue() }
    listOf(
        async { initA() },
        async { initB() },
    ).awaitAll()

    fooAsync.await()
}

suspend fun getFooValue(): String {
    delay(2_000)
    return "Foo"
}

suspend fun initA() = delay(1_000)
suspend fun initB() = delay(3_000)

[Joffrey]

You also don't even need to launch the other 2 using async, you could use lauch for the other 2 and not even await them (withContext would do it)

[Nino]

Wouldn't initA() and initB() become sequential this way ?

[Nino]

Nevermind, I need to use 2 launches obviously. The heat is killing my brain lol

Final code ? :

import kotlinx.coroutines.*

fun main() = runBlocking {
    println(initializeStuffAndGetFoo())
}

suspend fun initializeStuffAndGetFoo() = coroutineScope {
    launch { initA() }
    launch { initB() }
    getFooValue()
}

suspend fun getFooValue(): String {
    println("Waiting for foo value...")
    delay(2_000)
    println("Waiting for foo value done!")
    return "Foo"
}

suspend fun initA() {
    println("Waiting for A...")
    delay(1_000)
    println("Waiting for A done!")
} 
suspend fun initB() {
    println("Waiting for B...")
    delay(3_000)
    println("Waiting for B done!")
}

[Joffrey]

Exactly

[Nino]

Thanks a lot ! 🙂