InterlockedFactory.cs

public static class InterlockedFactory
{
    public static T GetOrCreate<T>(ref T value, Func<T> valueFactory) where T : class
    {
        if (ReferenceEquals(value, null))
        {
            if (valueFactory == null)
            {
                throw new ArgumentNullException("valueFactory");
            }
            var newValue = valueFactory();
            return Interlocked.CompareExchange(ref value, newValue, null) ?? newValue;
        }
        return value;
    }

    public static T GetOrCreate<T>(ref T value) where T : class, new()
    {
        if (ReferenceEquals(value, null))
        {
            var newValue = new T();
            return Interlocked.CompareExchange(ref value, newValue, null) ?? newValue;
        }
        return value;
    }
}