PHP session variable not getting incremented

PHP session variable not getting incremented

Here is what I am trying to do :
function increment_users($id){
$rooms = $_SESSION['rooms_array'];
//var_dump($rooms);
foreach ($rooms as $room) {
if($room['id'] == $id){$room['users']=$room['users']+1;}
}
session_write_close();
}
Room's users are not being incremented. I've checked session settings of
the server.? Thanks already.