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I want `scanAudios()` and `scanVideos()` to execut...
# coroutines
t
I want 
scanAudios()
and 
scanVideos()
to execute first before other stuff in this function.
Copy code
private suspend fun getFolderDataList(): List<FolderData> {
        thisScope.async() {
            scanAudios()
            scanVideos()
        }.await()

        val audioFolderData = viewModel.getAudioUris().map { uri ->
            FolderData("Audio", uri)
        }

        val videoFolderData = viewModel.getVideoUris().map { uri ->
            FolderData("Video", uri)
        }

        return audioFolderData.plus(videoFolderData)
    }
Am I doing it correctly?
d
Short answer is yes.
👀 1
I'm a little sceptical about the immediate 
await
after the 
async
, but it should do what you want.
Why have you used 
async
there?
t
I needed the function 
await()
. 
launch()
does not have it. 
launch()
only has 
invokeOnCompletion()
which I cannot use because the other code are also suspend functions.
d
launch
has 
join
.
Why not just call 
scanAudios
and 
scanVideos
without wrapping it in a coroutine?
t
oh I didn't know of 
join
. Let me check it out.
scanAudios
and 
scanVideos
need to complete first for the code after to be accurate.
d
Sure but you can do that without wrapping them.
The wrapping you've added there doesn't change anything with regards to ordering.
t
oh how do I wait for them without the 
join
or 
await
then?
d
Copy code
private suspend fun getFolderDataList(): List<FolderData> {
        scanAudios()
        scanVideos()

        val audioFolderData = viewModel.getAudioUris().map { uri ->
            FolderData("Audio", uri)
        }

        val videoFolderData = viewModel.getVideoUris().map { uri ->
            FolderData("Video", uri)
        }

        return audioFolderData.plus(videoFolderData)
    }
What do you mean by wait? What does 
scanAudios
do? It's a suspend function right?
t
are you sure 
getAudioUris()
and 
getVideoUris()
won't be executed when `scanAudios`/`scanVideos` are running?
yes 
scanAudios
is a suspend function. 
getAudioUris
and 
getVideoUris
are also suspend.
d
Yes, suspend functions suspend the coroutine when they are called. You only get concurrency when you introduce it with 
launch
or 
async
.
🙌 1
✅ 1
t
wait here means I want 
scanAudios
and 
scanVideos
to finish first before calls to 
getAudioUris
and 
getVideoUris
ohh
d
Do you also want scanAudios and scanVideos to run at the same time?
t
Thanks for the help. I haven't used coroutines for a while; I must have confused between concurrency and suspension.
👍🏼 1
yes I want them to run at the same time
d
Ah, in that case.....
Copy code
private suspend fun getFolderDataList(): List<FolderData> {
        coroutineScope {
            launch { scanAudios() }
            launch { scanVideos() }
        }

        val audioFolderData = viewModel.getAudioUris().map { uri ->
            FolderData("Audio", uri)
        }

        val videoFolderData = viewModel.getVideoUris().map { uri ->
            FolderData("Video", uri)
        }

        return audioFolderData.plus(videoFolderData)
    }
🙌 1
t
perfect. Thanks. Your code helps this part of the doc makes more sense now. https://kotlinlang.org/docs/composing-suspending-functions.html#concurrent-using-async
j
Calling suspend functions is like regular functions, they don't return until they're done. Using 
async{...}.await()
is pointless and actually equivalent to just calling the functions. The only difference here is you're using a particular scope, so the coroutine context could be different, but in terms of what waits and what doesn't it's equivalent
🙌 1
If you want to call 
scanAudios
and 
scanVideos
concurrently, it's another story. But it doesn't seem to be your goal here, so you can keep things very simple
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