https://kotlinlang.org logo
#coroutines
Title
# coroutines
p

Pablo

01/12/2021, 4:17 PM
Anyone of you can explain how retrofit / room are doing the main-safety stuff? I know that if I put suspend I can avoid the
withContext(<http://Dispatchers.IO|Dispatchers.IO>)
but what if I have some mappers and some business logic? Is it safe to remove the
withContext(<http://Dispatchers.IO|Dispatchers.IO>)
?
n

Nicholas Doglio

01/12/2021, 5:05 PM
Anyone of you can explain how retrofit / room are doing the main-safety stuff?
Under the hood both Retrofit and Room are delegating to their own way of handling async calls. For Room see this article: https://medium.com/androiddevelopers/room-coroutines-422b786dc4c5 For Retrofit the
suspend
calls just delegate to the built in
Call<T>.enqueue
which uses it’s own background executor. see https://github.com/square/retrofit/blob/master/retrofit/src/main/java/retrofit2/KotlinExtensions.kt
I know that if I put suspend I can avoid the 
withContext(<http://Dispatchers.IO|Dispatchers.IO>)
 but what if I have some mappers and some business logic? Is it safe to remove the 
withContext(<http://Dispatchers.IO|Dispatchers.IO>)
 ?
If the business logic and mappers are exclusively working with Room and Retrofit calls then yes it’s fine to remove them.
l

louiscad

01/12/2021, 6:19 PM
mapping and all should be done in
Dispatchers.Default
because it can consume a bunch of CPU (as all allocation can).
p

Pablo

01/13/2021, 7:56 AM
@louiscad Even if the mapper is not that big? I mean from now I have
<http://Dispatchers.IO|Dispatchers.IO>
unnecessary I guess because retrofit has it's own stuff, but when I'm getting the DTO I'm doing some mappers and sort etc, but it's super fast, do I have to use
Dispatchers.Default
anyways?.... I thought I had to change the Dispatcher when I have some heavy task that could work the UI
@Nicholas Doglio Thanks for that answer, it helped me a lot. My mappers are like from data to domain, and then in the use-case do some sorting stuff etc, or some other things (not that heavies though)
l

louiscad

01/13/2021, 8:43 AM
@Pablo "Not that big" can have very different meanins from one person to the other, but if you go from
<http://Dispatchers.IO|Dispatchers.IO>
to
Dispatchers.Default
without going through the main thread in between, there's no actual thread switching, so it's worth doing any computation/allocation/mapping in
Dispatchers.Default
by default, an switch to
<http://Dispatchers.IO|Dispatchers.IO>
when needed.
p

Pablo

01/13/2021, 9:11 AM
@louiscad I create a CorutineScope that is actually a
MainScope()
so, once I have that I do something like
Copy code
scope.launch{
//UI stuff
withContext(IO) { usecase call }
//UI stuff
}
The thing is my usecase calls my data source and datasource does a retrofit call, everything is suspend stuff, but the problem is once I have the DTO on datasource I do a mapper to convert it to domain, then in the use-case perhaps I sort or I'm doing something (not always...) For these cases do I have to change the dispatcher ? I mean I want to remove IO because I do not need it to call the retrofit call but under the hood I have more "logic" is not like get the data parsed from JSON and print it, no, I'm doing more stuff..
l

louiscad

01/13/2021, 9:12 AM
@Pablo IMO, only the strictly UI stuff should run on the main thread. You can wrap the whole everything else into
Dispatchers.Default { }
p

Pablo

01/13/2021, 9:17 AM
ok, so main thing like show dialog, show toast, and stuff like that is ok to run it on the
Dispatchers.Main
ok, but then if we have stuff like mappers/sortings/etc better on
Dispatchers.Default
I got confused because I've read that retrofit/room are main-safety so we can call them on the main thread
l

louiscad

01/13/2021, 9:18 AM
The thing is that doing a retrofit call might not be the only work that you need to do
p

Pablo

01/13/2021, 9:18 AM
But obviously, inside of that is not only the call, there's mappers and stuff.. so you recomend to me to use
Dispatchers.Default
, right instead?
l

louiscad

01/13/2021, 9:18 AM
Same for Room
If you do almost no allocation nor CPU consuming work besides getting the data from Room, retrofit or whatever that is "main-safe", maybe sticking to the main thread is fine.
p

Pablo

01/13/2021, 9:25 AM
Correct, but as I said in the comments, I do mapper sorting comparators things, that's more work, perhaps not much like doing a for loop of 1000000 elements, but it's something...
l

louiscad

01/13/2021, 9:25 AM
Yes, that's why I recommended to use
Dispatchers.Default
👍🏽 1
9 Views