온라인 인원수 계산 기능을 구현하는 PHP 방법

echo session_id();
//6ed364143f076d136f404ed93c034201<br />

bool session_set_save_handler ( callable $open , callable $close , callable $read , callable $write , callable$destroy , callable $gc )
//callable 可随时支取的，请求即付的，随时可偿还的
// open(string $savePath, string $sessionName) 打开连接
//close() 关闭连接
//read(string $sessionId) 对出数据
//write(string $sessionId, string $data) //写入数据
//destroy($sessionId) //删除数据
//gc($lifetime) //垃圾回收函数

session_set_save_handler(
   array("session","open"),
   array("session","close"),
   array("session","read"),
   array("session","write"),
   array("session","destroy"),
   array("session","gc")
);

//链接数据的open
function open($path,$sessname) {
  $db = mysql_connect("localhost","root","123456","test");
  mysql_select_db("test",$db);
  mysql_query("SET NAMES UTF8");
  return true;
}

function close(){
$db = mysql_connect("localhost","root","123456","test");
mysql_close($db);
return true;
}

function read($sid){
  $sql = "select data from session where sid='{$sid}' and card='".self::$card."'";
  $query = mysql_query($sql) or die(mysql_error());
  $row = mysql_fetch_array($query);
  $row>0?$row["data"]:" ";
}

function write($sid,$data)
{
   $sql = "select sid from session where sid='{$sid}' and card='".self::$card."'";
   $query = mysql_query($sql) or die(mysql_error());
   $mtime = time();
   $num = mysql_num_rows($query);
   if($num){
    $sql = "UPDATE session SET data='{$data}', mtime ='{$mtime}'";
   }else{
    $sql = "INSERT INTO session (sid,data,mtime,ip,card) VALUES('{$sid}','{$data}','".time()."','{$_SERVER['REMOTE_ADDR']}','".self::$card."')";
   }
   mysql_query($sql);
   return true;
}