something that has confused me with coroutines is that you often see things done with runBlocking. ...

# android

[Andy Gibel]

something that has confused me with coroutines is that you often see things done with runBlocking. Doesn't that sort of defeat the purpose of making a thing a suspend function?

[Andy Gibel]

For instance if you are on the main thread and calling into a viewModel to load from DB in a suspend function using the runBlocking builder - is that not equivalent to just calling the blocking version without using coroutines at all?

[bezrukov]

Just don't do that as much as possible. It was designed for the cases when you need to perform blocking operation.

[bezrukov]

From docs:

This function should not be used from a coroutine. It is designed to bridge regular blocking code to libraries that are written in suspending style, to be used in main functions and in tests.

[Andy Gibel]

I guess this goes back before coroutines to the argument that db INSERTs are fast enough for main thread.

[Andy Gibel]

most Room/Coroutine examples I see do this

[jw]

Those are wrong then

[Andy Gibel]

👍 Good to know. Trying to form a True North for coroutine usage. Seems to be lots of incorrect stuff out there.

[bezrukov]

Could you show these examples? Inserts may take a while if there is another transaction for example

[Andy Gibel]

Is it true then that correct usage of coroutine/Mvvm will most certainly make use of an async vehicle like LiveData or RxJava? (or Flow)

[Andy Gibel]

fun getAllSprockets(): List<Sprockets> = runBlocking {
    val deferred: Deferred<List<Sprockets>> = async {
      repository.getAllSprockets()
    }
    deferred.await()
  }

consider something like this as a public viewmodel interface

[Andy Gibel]

from what I'm hearing, this is flat wrong

[Andy Gibel]

which jives with my other opinion that having getters on a VM is an antipattern

[bezrukov]

wrapping repository call to async and then to runBlocking doesn't make any sense to me 🤷
it could be

suspend fun getAllSprockets() = repository.getAllSprockets()

if repository call is suspend fun
or

fun getAllSprockets() = repository.getAllSprockets()

if it blocking
or

suspend fun getAllSprockets() = runBlocking { return repository.getAllSprockets()
}

if repository call is suspend fun, but you need blocking

[Andy Gibel]

OK cool so it's not just me thinking this is weird 🙂 . In the first case you are exposing a suspend function to the consumer of the VM which I suppose is just moving the problem. Eventually I guess you'd want to use a launch or async builder to wrap that

[Andy Gibel]

for anyone following this thread - I found this very useful : https://proandroiddev.com/how-to-make-sense-of-kotlin-coroutines-b666c7151b93 . Best thing I've read yet to make sense of things