CacheFactory.cs

    public interface IFactory<T>
    {
        T Create();
    }

    public class CacheFactory<T> : IFactory<T>
    {
        private T cached;
        private readonly object syncLook = new object();

        public CacheFactory(IFactory<T> innerFactory)
        {
            if (innerFactory == null)
                throw new ArgumentNullException(nameof(innerFactory));

            this.InnerFactory = innerFactory;
        }

        public IFactory<T> InnerFactory { get; }

        public T Create()
        {
            lock (this.syncLook)
            {
                if (object.Equals(cached, default(T)))
                    this.cached = this.InnerFactory.Create();

                return this.cached;
            }
        }
    }