RE: [PHP] How to implement this by php Session

HI Chirs: thanks for your reply and opinion, so you mean I can know the alive session by reading /tmp ? I think that's only problem I want to know cause I affraid that I can't hold the dead or alive of session OK, I'll try to trace session by reading /tmp directory thanks a lot -----Original Message----- From: Chris Shiflett [mailto:shiflett@php.net] Sent: Thursday, January 23, 2003 2:54 AM To: Henry; php-general@lists.php.net; php-general@gremlins.biz Subject: Re: [PHP] How to implement this by php Session --- Henry <henry@cafelab.com> wrote: > what I want to do is make sure one account can login > in at the same time I understand now, with Jason's help. > is there any mechanism in PHP can slove it? Well, not exactly. You see, this is a rather strange restriction (or seems strange to me at least). There are two different data stores in a typical session management environment: 1. Session data store. This is all of those /tmp/sess* files if you are using the default setup. 2. User (or client) data store. This is where you would keep persistent data, such as username and password. You could store a login indicator in the user data store, so that when a user logs in, you make sure this flag is not set (else deny their login) and set it if it is not. This would work for a lot of cases, but it has a few notable problems: 1. It is not atomic. Under heavy load, you can experience synchronization problems where multiple clients check the flag, see that it is not set, and all try to set it. This is a rather unlikely prolem, but it is something to consider. 2. How do you know that someone is logged in? For example, if I login to your site (and you set my login flag to 1), how much inactivity will you tolerate before you consider me no longer logged in? Do you consider me logged in as long as I have a session record? What if I accidentally close my browser and go back to your site (and am not recognized due to my cookie being lost). Will you not allow me to log back in to your site until my login flag times out? I think this seems like a bad idea, but you might try this idea to see if it works well enough for you. Good luck. Chris -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php