C# singleton class

singleton.cs

/// SimpleLocker class avaliable at: https://gist.github.com/felipegtx/6107975
public sealed class SingletonFor<TheType>
{
    private static Func<TheType> _instanceBuilder = null;
    private Func<TheType> _constructorCall = null;
    private SimpleLocker _locker = null;
    private bool _isInitialized = false;
    private TheType _instance;

    public bool IsInitialized { get { return _locker.Read(() => _isInitialized); } }
    public bool UnprotectedIsInitialized { get { return _isInitialized; } }

    public SingletonFor(Func<TheType> constructorCall)
        : this(constructorCall, 1000) { }

    public SingletonFor(Func<TheType> constructorCall, int contructorLockTimeout)
    {
        if (_instanceBuilder == null) { _instanceBuilder = BuildInstance; }
        if (constructorCall == null) { throw new ArgumentNullException("constructorCall"); }
        _constructorCall = constructorCall;
        _locker = new SimpleLocker(contructorLockTimeout);
    }

    /// <summary>
    /// Changes the global builder for a given type
    ///     <remarks>This method should NEVER be used in a production code. It is intended only for creating detours for Unity Tests routines.</remarks>
    /// </summary>
    /// <param name="newGlobalBuilder">The builder body that is to be used globaly whenever an instance of this types is requested.</param>
    [Obsolete("This method should NEVER be used in a production code. It is intended only for creating detours for Unity Tests routines.")]
    public static void SetBuilderAs(Func<TheType> newGlobalBuilder)
    {
        _instanceBuilder = newGlobalBuilder;
    }

    public TheType GetInstance()
    {
        return _instanceBuilder();
    }

    private TheType BuildInstance()
    {
        if (!_locker.UpgradeableRead(() => this.UnprotectedIsInitialized))
        {
            _locker.WriteVoid(() =>
            {
                if (!this.UnprotectedIsInitialized)
                {
                    _instance = _constructorCall();
                    _isInitialized = true;
                }
            });
        }
        return this._instance;
    }
}