Question

I have a huge XML document which I have to parse it to generate domain objects.

Because the document is huge, i don’t want to parse it every time a user requests it, but only first time, then saving all the objects into cache.

public List<Product> GetXMLProducts()
{
    if (HttpRuntime.Cache.Get("ProductsXML") != null)
    {
        return (List<Product>)(HttpRuntime.Cache.Get("ProductsXML"));
    }

    string xmlPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Content\\Products.xml");
    XmlReader reader = XmlReader.Create(xmlPath);
    XDocument doc = XDocument.Load(reader);

    List<Product> productsList = new List<Product>();
    // Parsing the products element

    HttpRuntime.Cache.Insert("ProductsXML", productsList);
    return productsList;
}

How is the best way i can make this function working in singleton and be thread-safe?

Fixed the saving an object into cache method (was a copy-paste mistake)

Answer 1

Create a Lazy static and keep in memory for the lifetime of the application. And don’t forget the “true” part, that’s what makes it thread safe.

public static readonly Lazy<List<Product>> _product = new Lazy<List<Products>>(() => GetProducts(), true);

To add this to your model, just make it private and return _product.Value;

public MyModel
{
    ... bunch of methods/properties

    private static readonly Lazy<List<Product>> _products = new Lazy<List<Products>>(() => GetProducts(), true);

    private static List<Product> GetProducts()
    {
        return DsLayer.GetProducts();

    }

    public List<Product> Products { get { return _products.Value; } }
}

To create a singleton using Lazy<>, use this pattern.

public MyClass
{
    private static readonly Lazy<MyClass> _myClass = new Lazy<MyClass>(() => new MyClass(), true);

    private MyClass(){}

    public static MyClass Instance { get { return _myClass.Value; } }
}

Update/Edit:

Another lazy pattern for use within a context (i.e. Session)

Some Model that is saved in Session:

public MyModel
{
   private List<Product> _currentProducts = null;
   public List<Product> CurrentProducts 
   {
      get
      {
         return this._currentProducts ?? (_currentProducts = ProductDataLayer.GetProducts(this.CurrentCustomer));
      }
   }
}