做开发的时候我们可能需要不断轮询抓取网络数据。比如说如果要监控一个用户的微博feed更新，我们一般的解决方案是定时（如1分钟1次）查询服务器看看有没有新数据。但，请设想这么一种情形：

/**
*  变速器
*/
class Transmission
{
    private $mc ;
    private $account ;
    function __construct()
    {
        $this->mc = $GLOBALS['mmc'] ? $GLOBALS['mmc'] : memcache_init();
    }
    function set_account($account){
        $this->account = $account ;
    }
    //判断是否应该执行（根据时间判断）
    function is_execute(){
        $is_execute = 0 ;
        $next_execute_time = $this->get_next_time($this->account);
        if ($next_execute_time) {
           if ($next_execute_time < time() ) {
               $is_execute = 1 ;
           }
        }else{
            $is_execute = 1 ;
        }
        return $is_execute ;
    }
    //设置下次可执行的时间
    function set_next_time(){
        $times = $this->get_times($this->account);
        $times = $times > 30 ? 30 : $times+1 ;
        memcache_set($this->mc,'no_change_times_'.$this->account, $times , 0, 29*24*60*60 );
        $next_execute_time = time() + ($times+1)*60;//当前时间+(次数+1)*分钟
        memcache_set($this->mc,'next_execute_time_'.$this->account, $next_execute_time , 0, 29*24*60*60 );
    }
    //重置，恢复默认访问时间
    function reset(){
        //默认0次
        memcache_set($this->mc,'no_change_times_'.$this->account, 0 , 0, 29*24*60*60 );
        $next_execute_time = time() + 60;//当前时间+1分钟
        memcache_set($this->mc,'next_execute_time_'.$this->account, $next_execute_time , 0, 29*24*60*60 );
    }
    //获取次数
    function get_times(){
        $times = memcache_get($this->mc,'no_change_times_'.$this->account);
        return $times;
    }
    //获取下次执行时间
    function get_next_time(){
        $next_execute_time = memcache_get($this->mc,'next_execute_time_'.$this->account);
        return $next_execute_time;
    }
}