Hi) I'm a bit confused about coroutines on Android...

# coroutines

[ahulyk]

Hi)
I'm a bit confused about coroutines on Android:
Example 1:

launch(IO) {
            val result = repoRepository.getAllRepos()
            withContext(Main) {
                textField.text = result
            }
        }

Example 2:

launch(Main) {
            val result = repoRepository.getAllRepos()
            withContext(Main) {
                textField.text = result
            }
        }

Question is why i'm not getting android.os.NetworkOnMainThreadException in second example?

[streetsofboston]

Does getAllRepose() do the actual fetching from the network, or does it just block and waits for an other thread, that does the networking, to return the result.

[ahulyk]

getAllRepose() do the actual fetching from the network:

class RepoRepositoryImpl @Inject constructor(
        private val apiService: APIService
) : RepoRepository {

    override suspend fun getAllRepos(orgName: String) : List<RepoDto> {
        return apiService.getAllRepos(orgName).await()
    }

}

[streetsofboston]

But apiService.getAllRepos() does all the work, maybe on a different thread.

[streetsofboston]

The RepoRepositoryImpl.getAllRepos() may just wait (await()) for that other thread to return the result

[ahulyk]

APIService is just Retrofit Service:

interface APIService {

    @GET("/orgs/kotlin/repos")
    fun getAllReposRx(): Single<List<RepoDto>>

    @GET("/orgs/{org}/repos")
    fun getAllRepos(@Path("org") orgName: String): Deferred<List<RepoDto>>

}

[streetsofboston]

Yep. And retrofit may use its own (IO) Dispatcher.

[ahulyk]

Under the hood OkHttpClient uses new Thread() for network request - that is for sure

[louiscad]

There's no network on the main thread that would block it, there's just a coroutine suspending until some stuff done on another thread/dispatcher/executor completes and resumes it (and that stuff happens to do network I/O)

[streetsofboston]

Parsing doesn’t necessarily involve network communication. It maybe just parsing a string that is in memory

[ahulyk]

Looks like CoroutineCallAdapterFactory did the trick here 🙂

[ahulyk]

It uses Call callback. So Retrofit work asynchronous in that case!

[ahulyk]

Thank you!

[gildor]

Under the hood OkHttpClient uses new Thread() for network request - that is for sure

This is not exactly correct, OkHttp uses own dispatcher with thread pool

[ahulyk]

Yeap.