Umbraco-CMS/src/Umbraco.Web/PluginResolverExtensions.cs

using System;
using System.Collections.Generic;
using Umbraco.Core;
using Umbraco.Web.Routing;
using umbraco.BusinessLogic;
using umbraco.BusinessLogic.Utils;

namespace Umbraco.Web
{
    /// <summary>
    /// Extension methods for the PluginResolver
    /// </summary>
    public static class PluginResolverExtensions
    {

        private static volatile IEnumerable<ILookup> _lookups;
        private static readonly object Locker = new object();

        /// <summary>
        /// Returns all available ILookup objects
        /// </summary>
        /// <param name="plugins"></param>
        /// <returns></returns>
        internal static IEnumerable<ILookup> ResolveLookups(this PluginResolver plugins)
        {
            if (_lookups == null)
            {
                lock(Locker)
                {
                    if (_lookups == null)
                    {
                        var lookupTypes = TypeFinder.FindClassesOfType<ILookup>();
                        var lookups = new List<ILookup>();
                        foreach (var l in lookupTypes)
                        {
                            try
                            {
                                var typeInstance = Activator.CreateInstance(l) as ILookup;
                                lookups.Add(typeInstance);
                            }
                            catch (Exception ex)
                            {
                                Log.Add(LogTypes.Error, -1, "Error loading ILookup: " + ex.ToString());
                            }
                        }
                        //set the global
                        _lookups = lookups;
                    }
                }
            }
            return _lookups;
        }

    }
}