「カテゴリ」がわかりません。説明してください。

<?php<br />
<br />
class lock{<br />
private $num,$lock_marker,$lock_file,$timeout;<br />
public $islock;<br />
private function file_timeout(){<br />
if(file_exists($this->lock_file)){<br />
if(time()-filemtime($this->lock_file)>=$this->timeout){<br />
@unlink($this->lock_file);<br />
return true;<br />
}<br />
return false;<br />
}else return true;<br />
}<br />
function __construct($num=1,$timeout=3,$wait=false,$wait_time=0,$marker = ''){<br />
$this->num=$num;<br />
$marker ||$marker = $_SERVER['SCRIPT_FILENAME'];<br />
$marker = md5($marker);<br />
$this->lock_marker = $marker;<br />
$this->timeout=$timeout;<br />
$this->lock_file=d('./cache/lock/'.$this->lock_marker.$this->num.'.lock');<br />
if(file_exists($this->lock_file)){<br />
$this->islock=!$this->file_timeout();<br />
}else $this->islock=false;<br />
if(!$this->islock)touch($this->lock_file);<br />
else {<br />
if($wait){<br />
$wait_start=0;<br />
while(!$this->file_timeout()){<br />
if($wait_time>0){<br />
$wait_start+=100000;<br />
if($wait_start>$wait_time)break;<br />
}<br />
}<br />
file_exists($this->lock_file)&&@unlink($this->lock_file);<br />
touch($this->lock_file);<br />
$this->islock=false;<br />
}<br />
}<br />
}<br />
function __destruct(){<br />
$this->close();<br />
}<br />
public function close(){<br />
!$this->islock&&file_exists($this->lock_file)&&@unlink($this->lock_file);<br />
}<br />
}<br />
<br />
?>