[[MYCoreDataManager sharedInstance]doTaskwithCompletion:^(BOOL complete) {

                if (complete == YES) {

                    dispatch_async(dispatch_get_main_queue(), ^{

                         // back to the main thread
                    });
                }

            }];

-(void)doTaskwithCompletion:(coreDataCompletion)complete
  {
    [self.backgroundManagedObjectContext performBlock:^{

        // do my BG core data task

        [self saveContext:self.backgroundManagedObjectContext];
        complete(YES);

    }];
   }