PHPセッションの書き込みに失敗した場合の対処方法

Warning: session_write_close(): Failed to write session data using user defined save handler. (session.save_path: tcp://127.0.0.1:6379) in /var/www/html/php/libs/util/Session.php on line 43

class Session {
  // single ton
  private static $session_handler_;
  public static function Init() {
    if (!isset(self::$session_handler_))
      self::$session_handler_ = new Session();
  }
  // 阻止用户复制对象实例
  public function __clone() {
    trigger_error('Clone Session is not allowed.', E_USER_ERROR);
  }
  private function __construct() {
    session_set_save_handler(array($this, "Open"),
                             array($this, "Close"),
                             array($this, "Read"),
                             array($this, "Write"),
                             array($this, "Destroy"),
                             array($this, "Gc"));
    // for web user
    $session_id = Cookie::Get(SESSIONID);
    /* length of session id
     128-bit digest (MD5)
     4 bits/char: 32 char SID
     5 bits/char: 26 char SID
     6 bits/char: 22 char SID
     160-bit digest (SHA-1)
     4 bits/char: 40 char SID
     5 bits/char: 32 char SID
     6 bits/char: 27 char SID
    */
    if (!empty($session_id) && 26 == strlen($session_id))
      session_id($session_id);
    session_start();
  }
  public function __destruct() {
    session_write_close();
  }
  public function Open($save_path, $session_name) {
    return true;
  }
  public function Close() {
    return true;
  }
  public function Read($session_id) {
    $key = SESSION_PREFIX . $session_id;
    $memcached_client_ = SessionMemCachedClient::GetInstance();
    return (string)$memcached_client_->get($key);
  }
  public function Write($session_id, $data) {
    $key = SESSION_PREFIX . $session_id;
    $memcached_client_ = SessionMemCachedClient::GetInstance();
    if ($data)
      return $memcached_client_->set($key, $data, SESSION_EXPIRE_TIME);
    return true;
  }
  public function Destroy($session_id) {
    $key = SESSION_PREFIX . $session_id;
    $memcached_client_ = SessionMemCachedClient::GetInstance();
    return $memcached_client_->delete($key);
  }
  public function Gc($maxlifetime) {
    return true;
  }
}
Session::Init();