nl_tokens: 从当前节点的 next 开始，依次将所有可用的节点全部加载满
pl_tokens: public long load ( ) throws IOException { if ( item . isStreamEnd ) return readed ; RingItem ri = item ; while ( ! ri . isLoaded ) { ri . load ( ins ) ; if ( ri . <mask> > 0 ) readed += ri . max ; ri = ri . next ; } return readed ; }