Anyone of you can explain how retrofit / room are ...

# coroutines

[Pablo]

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>) ?

[Nicholas Doglio]

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.

[louiscad]

mapping and all should be done in Dispatchers.Default because it can consume a bunch of CPU (as all allocation can).

[Pablo]

@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

[Pablo]

@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)

[louiscad]

@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.

[Pablo]

@louiscad I create a CorutineScope that is actually a MainScope() so, once I have that I do something like

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..

[louiscad]

@Pablo IMO, only the strictly UI stuff should run on the main thread. You can wrap the whole everything else into Dispatchers.Default { }

[Pablo]

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

[Pablo]

I got confused because I've read that retrofit/room are main-safety so we can call them on the main thread

[louiscad]

The thing is that doing a retrofit call might not be the only work that you need to do

[Pablo]

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?

[louiscad]

Same for Room

[louiscad]

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.

[Pablo]

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...

[louiscad]

Yes, that's why I recommended to use Dispatchers.Default