Units of Measure Validator for C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace HDLibrary.UnitsOfMeasure
{
    public static class GlobalUnitParser
    {
        private static object syncRoot = new object();

        private static IUnitParser instance;
        public static IUnitParser Instance
        {
            get
            {
                lock (syncRoot)
                {
                    if (instance == null)
                    {
                        instance = ComposedUnitParser.NewDefaultUnitParser();
                        var library = XmlUnitLibrary.NewDefaultLibrary();
                        library.LoadTo(((ComposedUnitParser)instance).GetUnitRegistry(), instance);
                    }
                }
                return instance;
            }
        }

        public static void Initialize(IUnitParser unitParser)
        {
            if (unitParser == null)
                throw new ArgumentNullException("unitParser");

            lock (syncRoot)
            {
                if (instance != null)
                    throw new InvalidOperationException("Global unit parser is already initialized!");

                instance = unitParser;
            }
        }
    }
}