Example of main thread safety for Core data

gistfile1.m

//RCCoreData helper class

+(BOOL) onMainThread:(void (^)(void))mainThreadOperation
{
    BOOL isMainThread = [NSThread isMainThread];
    NSAssert(isMainThread, @"Should be on main thread");
    if (isMainThread) {
        mainThreadOperation();
    } else {
        dispatch_async(dispatch_get_main_queue(), mainThreadOperation);
    }
    return isMainThread;
}

// Your tableview NSFetchedResultsController delegate

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [RCApplication onMainThread:^{
        [self.tableView beginUpdates];
    }];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [RCApplication onMainThread:^{
        [self.tableView endUpdates];
    }];
}