Cannot access database on the main thread - Android Room - Using ThreadPoolExecutor

Question

I'm getting that famous error "Cannot access database on the main thread since it may potentially lock the UI for a long periods of time" But from what I understand, I'm not accessing the database in main thread since I'm executing the call inside a Runnable executed by a ThreadPoolExecutor. What am I doing wrong?

In the following method, I'm using a runnable to obtain data from network and store it in a local database.

private void refresh() {
    executor.execute(() -> {
        if (!dataSource.hasData()) {
            recipeService.getAllRecipes().enqueue(new Callback<List<Recipe>>() {
                @Override
                public void onResponse(Call<List<Recipe>> call, Response<List<Recipe>> response) {
                    dataSource.save(response.body());
                }

                @Override
                public void onFailure(Call<List<Recipe>> call, Throwable t) {
                    throw new RuntimeException(t);
                }
            });
        }

    });
}

DataSource.save:

@Override
    public void save(List<Recipe> recipes) {
        for (Recipe recipe : recipes) {
            recipeDao.insert(recipe);
            int count = 1;

            for (Ingredient ingredient : recipe.getIngredients()) {
                ingredient.setId(count++);
                ingredient.setRecipeId(recipe.getId());
                ingredientDao.insert(ingredient);
            }

            for (Step step : recipe.getSteps()) {
                step.setRecipeId(recipe.getId());
                stepDao.insert(step);
            }

        }
    }

The executor is defined as:

@Provides
Executor executor() {
    return new ThreadPoolExecutor(4, 8, 60,
            TimeUnit.SECONDS, new LinkedBlockingQueue<>());
}

Error I'm getting:

06-18 03:03:38.653 27231-27231/com.github.alexpfx.udacity.nanodegree.android.baking_app E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.github.alexpfx.udacity.nanodegree.android.baking_app, PID: 27231
java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long periods of time.
at android.arch.persistence.room.RoomDatabase.assertNotMainThread(RoomDatabase.java:137)
at android.arch.persistence.room.RoomDatabase.beginTransaction(RoomDatabase.java:184)
at com.github.alexpfx.udacity.nanodegree.android.baking_app.data.local.RecipeDao_Impl.insert(RecipeDao_Impl.java:89)
at com.github.alexpfx.udacity.nanodegree.android.baking_app.recipe.RecipeLocalDataSource.save(RecipeLocalDataSource.java:34)
at com.github.alexpfx.udacity.nanodegree.android.baking_app.recipe.RecipesRepositoryImpl$1.onResponse(RecipesRepositoryImpl.java:49)
at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6776)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1496)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1386)

Answer 1

seems that your callback.onresponce() method call is from UI thread

changing your onResponse method like this can help

@Override
public void onResponse(Call<List<Recipe>> call, Response<List<Recipe>> response) {
AsyncTask.execute(new Runnable() {
                    @Override
                    public void run() {
                        dataSource.save(response.body());
                    }
                });

            }