Question

I have to perform a fetch via NSFetchedResultsController on a background thread.

My current solution is structured like that:

dispatch_queue_t fetchQueue = dispatch_queue_create("backgroundfetching", NULL);

dispatch_async(fetchQueue,^{
    // 1. Create NSManagedObjectContext
    // 2. Create NSFetchRequest
    // 3. Create NSFetchedResultsController
    // 4. PerformFetch

    dispatch_async(dispatch_get_main_queue(),^{
        [[self table] reloadData];
    });
});

dispatch_release(fetchQueue);

My first tests ran well but is that the appropriate way?

Answer 1

Since the fetched results controller is intended to control the data that defines a tableview, it belongs on the foreground thread/operation that the UI runs on. It’s rather pointless to put it on a background thread as you would lose all the advantages of using it in the first place.

I would also be concerned about the effects of sending the FRC delegate messages across asynchronous threads. I’m not sure how reliable that would be.

Having said all that, the sketch of your implementation looks fine as far as it goes.