Hi! I'm trying to parallelize some work, to improv...

# coroutines

[iex]

Hi! I'm trying to parallelize some work, to improve performance. Am I doing it right?

override fun foo(): List<String> =
    runBlocking {
        fooSuspended()
    }

suspend fun fooSuspended(): List<String> =
    coroutineScope {
        val res: List<Deferred<String?>> = (1..100).map { n ->
            async {
                doWork()
            }
        }
        res.mapNotNull { it.await() }
    }

fun doWork(): String? {
    Thread.sleep(500)
    return "hi"
}

[octylFractal]

you may want to specify a different dispatcher, otherwise it'll still be single-threaded due to `runBlocking`'s event loop. an easy way is runBlocking(Dispatcher.Default) { ... }

[iex]

thanks!!

[octylFractal]

another alternative is to specify the dispatcher as close to where it's actually needed as possible, in that case you could do async(Dispatcher.Default) { ... } and achieve a similar effect

[iex]

"unresolved reference: Default" 😕

[octylFractal]

oh, it might be Dispatchers? been a bit

[iex]

that's it! Dispatcher was from ok http

[iex]

oh NICE went from 50s to 17s 🙂

[Dominaezzz]

Might be even faster with <http://Dispatchers.IO|Dispatchers.IO> since you're blocking with Thread.sleep .

[iex]

in my actual code I'm doing computations. Maybe, still?

[streetsofboston]

Instead of res.mapNotNull { it.await() }, what if you tried res.awaitAll().mapNotNull() ?
It shouldn’t matter much, since all `async`s are kicked off at the same time, but I’m curious 🙂

[iex]

ok, tried out IO anyway and confirm that it's not good for computations. It duplicated the time 😅

[Dominaezzz]

Yeah, definitely worse for computation.

[iex]

awaitAll().mapNotNull() doesn't change the time

[iex]

but I'll use it, it seems more idiomatic

[Dominaezzz]

It is also less error-prone. Especially when laziness is involved.

[iex]

hmm this is very strange, the emulator (differently to the devices) is taking 2x longer with the coroutines...

[iex]

compared to executing everything in the same thread

[iex]

I guess the emulator doesn't support properly multiple cores?

[Dominaezzz]

That's my guess too.