Hey, sorta new here, coming from Golang. I was af...

# getting-started

[Ani Mehta]

Hey, sorta new here, coming from Golang.

I was after a replacement for waitGroup, build my own, shockingly bad one...

// TODO: Fix this hacky parallelism
var awaitingResponse = 0
for (v in needsResponses) {
    GlobalScope.launch {
        while (awaitingResponse >= 30) {
            delay(5)
        }
        awaitingResponse++
        // send API request, record response
        awaitingResponse--
    }
}

sleep(1000) // needed in order to not just skip before any request is sent off
while (awaitingResponse > 0) {
    sleep(5000)
}

For reference it iterates over a map in parallel, what's a better way of doing this? There's an issue currently where it sometimes proceeds before all responses are fetched/ recorded

[Robert]

What is “needsResponse” ?
If you run them as async https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/async.html you’ll get a Deferred
<T> which you can store an later awaitAll https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/await-all.html

[elizarov]

Just use structured concurrency and you will not need waitgroup at all. On side note, you’ll get better help in #coroutines channel.

[Evan R.]

What Roman said. Because coroutines use structured concurrency, you can wrap your code in a suspending function or runBlocking { }, then throw your for loop in a coroutineScope { } , drop GlobalScope, and the coroutineScope will both:

1. Wait for all launched coroutines to complete
2. Throw any exception from said coroutines and automatically cancel the others
Coroutines handles a lot of stuff that goroutines don’t.

[Evan R.]

Updated code will look like this:

Untitled