PHP cache file cache_PHP tutorial

<?php
class Cache_Driver{
	//定义缓存的路径
	protected $_cache_path;

//根据$config中的cache_path值获取路径信息
	public function Cache_Driver($config)
	{
		if(is_array($config) && isset($config[&#39;cache_path&#39;]))
		{
		   $this->_cache_path = $config[&#39;cache_path&#39;];
		}
		else
		{
		   $this->_cache_path = realpath(dirname(__FILE__)."/")."/cache/";
		}
	}
//判断key值对应的文件是否存在，如果存在，读取value值，value以序列化存储
	public function get($id)
	{
		if ( ! file_exists($this->_cache_path.$id))
		{
			return FALSE;
		}
		
		$data = @file_get_contents($this->_cache_path.$id);
		$data = unserialize($data);
		
		if(!is_array($data) || !isset($data[&#39;time&#39;]) || !isset($data[&#39;ttl&#39;]))
		{
			return FALSE;
		}
		
		if ($data[&#39;ttl&#39;] > 0 && time() >  $data[&#39;time&#39;] + $data[&#39;ttl&#39;])
		{
			@unlink($this->_cache_path.$id);
			return FALSE;
		}
		
		return $data[&#39;data&#39;];
	}
//设置缓存信息，根据key值，生成相应的缓存文件
	public function set($id, $data, $ttl = 60)
	{		
		$contents = array(
				&#39;time&#39;		=> time(),
				&#39;ttl&#39;		=> $ttl,			
				&#39;data&#39;		=> $data
			);
		
		if (@file_put_contents($this->_cache_path.$id, serialize($contents)))
		{
			@chmod($this->_cache_path.$id, 0777);
			return TRUE;			
		}

		return FALSE;
	}
//根据key值，删除缓存文件
	public function delete($id)
	{
		return @unlink($this->_cache_path.$id);
	}

	public function clean()
	{
      $dh = @opendir($this->_cache_path);
	   if(!$dh)
         return FALSE;
      
      while ($file = @readdir($dh))
      {
         if($file == "." || $file == "..")
            continue;
         
         $path = $this->_cache_path."/".$file;
         if(is_file($path))
            @unlink($path);
      }
      @closedir($dh);
      
		return TRUE;
	}
}