php实现多站点共用session实现单点登录的方法详解

$back = login($name,$pwd);//执行登陆操作,成功就写入session
//如果登录成功，进行以下操作流程
if($back){
  $sessionid = session_id();
  $key = encode($session,$keyword);//生成安全码
  //输出一个登陆成功提示页，并跳转到请求登陆的站点
}

//解密$key
decode($key);
//把当前站点的sessionid设置为传递的sessionid
session_id($_GET['sessionid']);
session_start();

$gb_DBname="test";            //数据库名称
$gb_DBuser="root";            //数据库用户名称
$gb_DBpass="";              //数据库密码
$gb_DBHOSTname="127.0.0.1";        //主机的名称或是IP地址
$SESS_DBH="";              //数据库对象
session_module_name("User");      //定义session存储按用户定义的方式
$SESS_LIFE=get_cfg_var("session.gc_maxlifetime");//得到session的最大有效期,也可以自定义
function sess_open($save_path,$session_name)
{
  global $gb_DBHOSTname,$gb_DBname,$gb_DBuser,$gb_DBpass,$SESS_DBH;
  if(!$SESS_DBH=mysql_pconnect($gb_DBHOSTname,$gb_DBuser,$gb_DBpass)){
  echo "MySql Error:".mysql_error()."";
  die();
  }
  if(!mysql_select_db($gb_DBname,$SESS_DBH)){
  echo "MySql Error:".mysql_error()."";
  die();
  }
  return true;
}
function sess_close(){
return true;
}
function sess_read($key)
{
  global $SESS_DBH,$SESS_LIFE;
  $qry="select value from db_session where sesskey = '$key' and expiry > ".time();
  $qid=mysql_query($qry,$SESS_DBH);
  if(list($value)=mysql_fetch_row($qid)){
  return $value;
  }
  return false;
}
//写入session信息。保存session信息的数据表名为：db_session
//除了主键自增id，需要的字段如下
//sesskey  sessionid
//values  session值
//expiry  session的到期日期
function sess_write($key,$val)
{
  global $SESS_DBH,$SESS_LIFE;
  $expiry=time()+$SESS_LIFE;
  $value=$val;
  $qry="insert into db_session values('$key',$expiry,'$value')";
  $qid=mysql_query($qry,$SESS_DBH);
  if(!$qid){
  $qry="update db_session set expiry=$expiry, value='$value' where sesskey='$key' and expiry >".time();
  $qid=mysql_query($qry,$SESS_DBH);
  }
  return $qid;
}
function sess_destroy($key)
{
  global $SESS_DBH;
  $qry="delete from db_session where sesskey = '$key'";
  $qid=mysql_query($qry,$SESS_DBH);
  return $qid;
}
function sess_gc($maxlifetime)
{
  global $SESS_DBH;
  $qry="delete from db_session where expiry < ".time();
  $qid=mysql_query($qry,$SESS_DBH);
  return mysql_affected_rows($SESS_DBH);
}
session_set_save_handler("sess_open","sess_close","sess_read","sess_write","sess_destroy","sess_gc");