php代码：
<?php
session_id(md5($id));//用id做为sessionid
session_start();
if(!isset($_SESSION['i'])){
$_SESSION['i'] = i();//获取库存
}
if($_SESSION['i'] > 0){
$buy = true;
$_SESSION['i']--;
}else{
$buy = false;
}
session_write_close();
if(isset($_COOKIE['PHPSESSID'])){//还原原来的session
session_id($_COOKIE['PHPSESSID']);
session_start();
}
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