How to provide an object using hilt in background thread with coroutine-CodePudding

I want to provide a realm object in the background thread like this:


@Module
@InstallIn(SingletonComponent::class)
object DatabaseModule {

    @Provides
    @Singleton
    fun provideDatabaseScope(): CoroutineScope = GlobalScope   Dispatchers.IO

    @Provides
    @Singleton
    fun provideDatabaseQueue(): ExecutorCoroutineDispatcher =
        Executors.newSingleThreadExecutor().asCoroutineDispatcher()

    @Provides
    @Singleton
    fun provideGetRealmConfig(accountService: AccountService): GetRealmConfig =
        GetRealmConfig(accountService)

    @Provides
    fun provideRealmConfig(
        getRealmConfig: GetRealmConfig,
        @ApplicationContext context: Context,
        accountService: AccountService
    ): RealmConfigImpl = RealmConfigImpl(getRealmConfig, accountService, context)


    @Provides
    fun provideRealmCreator(
        realmConfigImpl: RealmConfigImpl,
        scope: CoroutineScope,
        queue: ExecutorCoroutineDispatcher
    ): Realm {
        return RealmCreator(realmConfigImpl, scope, queue).createRealmObject()!!
    }

    @Provides
    @Singleton
    fun provideUserDatabase(
        realm: Realm,
        databaseScope: CoroutineScope,
        databaseQueue: ExecutorCoroutineDispatcher
    ): UserDataStorage = UserDataStorageImpl(realm, databaseScope, databaseQueue)
}

and this is RealmCreator class that creates the object in the background thread:

class RealmCreator @Inject constructor(
    val realmConfigImpl: RealmConfigImpl,
    val coroutineScope: CoroutineScope,
    val executorCoroutineDispatcher: ExecutorCoroutineDispatcher
) {
    var realm: Realm? = null
    fun createRealmObject(): Realm? {

        coroutineScope.launch(executorCoroutineDispatcher) {
            try {
                realm = Realm.getInstance(realmConfigImpl.realmConfiguration!!)
                countDownLatch.countDown()
            } catch (e: Exception) {
                e.printStackTrace()

            }
        }

        return realm
    }
}

when I want to create a Realm object it returns null because this process is in a background thread. How can I create this object in this situation?

CodePudding user response：

Apart from your intention of realm object creation in the background, your code is an example of Unstructured Concurrency. You're passing CoroutineScope in the constructor. You need to use coroutineScope() as a global suspend function that creates a new CoroutineScope under the hood and then executes the suspend function you pass with it in the body, and wait for it (and all its children) to complete before returning. It is a suspend function so you cannot call it outside of a coroutine like createRealmObject().

CodePudding user response：

I think you could use Provider in dagger. Reffer to this link.