是否可以从其他会话中访问$ _SESSION变量？

Question

My website uses sessions for user logins and I would like to have a message on each page showing the user how many computers are logged into their account (like what Gmail does).

For example, if they are logged in on two different computers, I would like the message to say:

You are logged in on 2 computers.

I know how to check if they are logged in -- I just check the $_SESSION['username'] variable and if it's set then they are logged in on that computer. But how can I check if the same username is set in other sessions (indicating that they are logged in on other computers)?

Answer 1

This is very difficult to do with the default file based PHP sessions. By default PHP just stores session information in an opaque blob in a file in the file system, with the name of the file being the session id. You have no direct access to the data in those files without opening them all one by one and evaluating them.

What you need is to move that information into a database. Either store only the number of concurrent logins in the database and keep the other sessions as is, but that's hard to keep in sync. It's better to switch to a complete database backend for sessions in lieu of the file based storage. This allows you to transparently query any data in sessions, including easily taking statistical information about how many sessions a user has.