从同时包含数字列表的文件中获取唯一的数字

I have a list of unique numbers in a file. Whenever user of my sites makes a request i need to fetch a value from that list , such that no other user gets the same value. There could be many concurrent requests, and hence the major issue is that of guaranteeing that no two users get the same value. I am not that concerned with performance in the sense that user doesn't expect any reply after making a request and so everything can happen in the background. From what i have read, this could be implemented using file locks or i could store data in the db and use db locks. I just want to get an ideas what is the best way of doing this thing. I am using postresql as my database and was wondering if this could be done using sequences where i store the current row number in the sequence so that my program knows which row to read from the db. But again i am not sure how to prevent multiple processes reading the same row before any one of them has a chance to update it. I have a list of unique numbers in a file. When