gistfile1.cs

using System;
using Sitecore.Caching;
using Sitecore.ContentSearch;

namespace MyProject
{
    public class MyContext
    {
        private static readonly ItemsContext _items;

        public static ItemsContext Items
        {
            get
            {
                return _items;
            }
        }

        static MyContext()
        {
            _items = new ItemsContext();
        }

        /// <summary>
        /// An example of executing code just once per request
        /// The actual example is quite contrived :)
        /// </summary>
        public static ISearchIndex SearchIndex
        {
            get
            {
                const string key = "ContentSearchIndex";
                if (Items[key] == null)
                {
                    if (Sitecore.Context.Database == null)
                    {
                        throw new Exception("Sitecore.Context.Database cannot be null");
                    }

                    Items[key] = Sitecore.Context.Database.Name == "web"
                                     ? ContentSearchManager.GetIndex("sitecore_web_index")
                                     : ContentSearchManager.GetIndex("sitecore_master_index");
                }

                return (ISearchIndex)Items[key];
            }
        }
    }
}

Especially as it doesn't account for the database potentially being switched during the request ;-)