I have 2 question: 1. If there is an item, each person is limited to one. It could be bought by a currency or real money or just increase from cloud code. What should i do to limit the count? 2. If there is an virtual purchase have a limit of 5 times per person. How could i do? I saw some cloud code apis have a parameter said "writelock". Is it used in these situation? How to use them?