php防止快速刷新的方法

<?php 
session_start(); 
$allow_sep = "20"; 
if (isset($_SESSION["post_sep"])) 
{ 
  if (time() - $_SESSION["post_sep"] < $allow_sep) 
  { 
  exit("你的速度是否似乎超出我的处理能力了^_^!"); 
} 
else 
{ 
  $_SESSION["post_sep"] = time(); 
} 
} 
else 
{ 
  $_SESSION["post_sep"] = time(); 
} 
?>