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k

Kulwinder Singh

12/21/2018, 9:22 AM
Ho to make this call async
videosList.forEachIndexed { index, video: BaseVideo ->
            val userData = getUserData(video)*//calling suspend function* 
            listWithData[index].userData = userData
        }
g

gildor

12/21/2018, 9:29 AM
val result: List<UserData> = videosList.map { video ->
   async { getUserData(video) }
}.awaitAll()
But in this case you do not limit concurrency
k

Kulwinder Singh

12/21/2018, 9:37 AM
"But in this case you do not limit concurrency" h
What does this mean , please explain
g

gildor

12/21/2018, 9:37 AM
it means that each item of videosList will start own coroutine
it may be fine
depends on what getUserData does
k

Kulwinder Singh

12/21/2018, 9:38 AM
so does it effect perfomance
?
coroutine itself is cheap.
k

Kulwinder Singh

12/21/2018, 9:39 AM
getUserData just get Document from Firestore collection
g

gildor

12/21/2018, 9:40 AM
don’t know how it works, so have no advices
just mention that it doesn’t limit concurrency
if you want limit amount of concurrent coroutines you need working pool pattern implementation
I recommend you watch this talk from KotlinConf by Roman

https://www.youtube.com/watch?v=a3agLJQ6vt8

👍 1
k

Kulwinder Singh

12/21/2018, 9:41 AM
Yes, thanks for link, i will definitely check it out
g

gildor

12/21/2018, 9:44 AM
Actually, in your case you have also simple way to limit amount of parallel tasks, just use chunked:
val result: List<UserData> = videosList.chunked(PARALLEL_COROUTINES_AMOUNT).flatMap { videos -> 
   videos.map { video ->
        async { getUserData(video) }
    }.awaitAll()
}
k

Kulwinder Singh

12/21/2018, 9:57 AM
But here i know in advance that how many items
videosList
is having , it has only 5 items ,so i don't think i have to convert it to
chucked
. i'm paginating
RecyclerView
loading data 5 items each time
g

gildor

12/21/2018, 10:02 AM
Then don’t worry about concurrency
k

Kulwinder Singh

12/21/2018, 10:11 AM
But still i think that what would happen if user scrolls list lot of time ,then there will be many
async
coroutines
created ,so how much it will effect ?
g

gildor

12/21/2018, 10:37 AM
as I said, it depends on getUserData implementation
k

Kulwinder Singh

12/21/2018, 10:51 AM
private suspend fun getUserData(video: BaseVideo): UserDataAboutVideo? {
        return if (currentUser != null) {
            val userDataDocument = firestore.getUserDataAboutVideos(currentUser!!.uid)
                    .document(video.videoId).get().await()

            if (userDataDocument.exists())
                userDataDocument.toObject(UserDataAboutVideo::class.java)!!
            else
                null

        } else null
    }
await implementation is
suspend fun <T> Task<T>.await(): T {
    return suspendCoroutine { continuation ->
        this.addOnCompleteListener { result ->
            if (result.result != null && result.isSuccessful)
                continuation.resume(result.result!!)
            else
                continuation.resumeWithException(result.exception?.cause!!)
        }
    }
}
g

gildor

12/21/2018, 10:59 AM
I have no idea how Firestore is implemented and work with multiple parallel requests
k

Kulwinder Singh

12/21/2018, 11:12 AM
ok, No problem, thanks for your all suggestions 👍
your answers helped me alot
g

gildor

12/21/2018, 2:08 PM
👍