Channel9Downloader.DataAccess.CategoryRepository.GetCategories C# (CSharp) Method

        public Categories GetCategories()
        {
            lock (_categoryLock)
            {
                if (_categories != null)
                {
                    return _categories;
                }

                var filename = CreateFilenameForCategory();
                _categories = _categoriesDataAccess.LoadCategories(filename);

                if (_categories == null)
                {
                    RetrieveCategories();
                }

                return _categories;
            }
        }