PHP实现负载均衡下的session共用功能

$_ENV=array(
  'SYS'=>array(
    'Memip'=>'127.0.0.1',      //MEMCACHE的ip
    'Mempt'=>11211,       //MEMCACHE的port
    'Memtim'=>10,          //MEMCACHE的超?r?r?g
  )
);
//托管SESSION到MEMCACHE,如果开启失败,则说明MEMCACHE没有配置正确
final class S{
  public static function open(){
  //禁止session自动开启
    session_write_close();
  ini_set('session.auto_start',0);
  //使用五十分之一的概率启动gc清理会话
  ini_set('session.gc_probability',1);
  ini_set('session.gc_divisor',50);
  ini_set('session.use_cookies',1);
  //session的寿命
  //ini_set('session.gc_maxlifetime',$_ENV['SYS']['Memtim']);
  //ini_set('session.cookie_lifetime',$_ENV['SYS']['Memtim']);
  //ini_set('session.save_handler','files');
  //ini_set('session.save_path',Run.'_tmp');
  //ini_set('session.save_handler','memcache');
  //ini_set('session.save_path','tcp://127.0.0.1:11211');
    //$_ENV['S_tim'] = ini_get('session.gc_maxlifetime');
  //建立memcache对象
  $_ENV['S_mem']=new Memcache;
  $_ENV['S_mem']->connect($_ENV['SYS']['Memip'],$_ENV['SYS']['Mempt']) or die('Memcache?B接失??!');
    return TRUE;
  }
  /**
    读取
    返回:读到的?热?
  /**/
  public static function read($id){
    return $_ENV['S_mem']->get('s_'.$id);
  }
  /**
    写入
    返回:bool
  /**/
  public static function write($id,$data){
    return $_ENV['S_mem']->set('s_'.$id,$data,MEMCACHE_COMPRESSED,$_ENV['SYS']['Memtim']);
  }
  /**
    关闭
    返回:bool
  /**/
  public static function close(){
    $_ENV['S_mem']->close();
    unset($_ENV['S_mem'],$_ENV['SYS']['Memtim']);
    return TRUE;
  }
  /**
    ?h除
    返回:bool
  /**/
  public static function destroy($id){
    return $_ENV['S_mem']->delete('s_'.$id);
  }
  /**
    清理
    返回:bool
  /**/
  public static function gc(){
    return TRUE;
  }
}
session_set_save_handler('S::open','S::close','S::read','S::write','S::destroy','S::gc');
$_ENV['sessionid']=(isset($_REQUEST['sessionid'])) ? trim($_REQUEST["sessionid"]) : session_id();
if($_ENV['sessionid']!=''){session_id($_ENV['sessionid']);}
session_start();