Question

I need to implement a system to limit the number of users that can concurrently use my app. I am thinking the best way to go is to count the number of sessions currently active and then limit based on that.

How can I count the number of sessions currently active. I am using memcached to store my sessions if that makes a difference

Answer 1

I think the easiest way is to intercept the session’s open, destroy and gc callbacks (using session_set_save_handler()) and increment/decrement a session count value within memcached. Something like:

class Memcache_Save_Handler {

   private $memcached;

   public function open($save_path, $name) {
      $session_count = (int)$this->memcached->get('session_count');
      $this->memcached->set('session_count', ++$session_count);
      // rest of handling...
   }

   public function destroy($id) {
      $session_count = (int)$this->memcached->get('session_count');
      $this->memcached->set('session_count', --$session_count);      
      // rest of handling...
   }

}