有谁知道这段代码什么意思？

obj = new ex_memcache(); $this->obj->init(array('server' => $ex_memcache_server,'port' => $ex_memcache_port,'pconnect' => $ex_memcache_pconnect,'timeout' => $ex_memcache_timeout,)); $this->obj->enable || $this->obj = null; $this->__cache_type = 'Memcached'; } if(!is_object($this->obj) && function_exists('eaccelerator_get') && $ex_eaccelerator){ $this->obj = new ex_eaccelerator(); $this->obj->init(); $this->__cache_type = 'eAccelerator'; } if(!is_object($this->obj) && function_exists('xcache_get') && $ex_xcache){ $this->obj = new ex_xcache(); $this->obj->init(); $this->__cache_type = 'xcache'; } if(!is_object($this->obj) && $ex_secache){ $this->obj = new ex_secache(); $this->obj->init(array('size' => $ex_secache_size,'datafile' => M_ROOT."dynamic/secache/cachedata",)); $this->obj->enable || $this->obj = null; $this->__cache_type = 'secache'; } $this->keys = array(); if(is_object($this->obj)){ $this->enable = true; $this->type = str_replace('ex_','',get_class($this->obj)); $this->keys = $this->get('ex_cache_keys'); is_array($this->keys) || $this->keys = array(); if(!($this->lastclearexpire = $this->get('lastclearexpire'))) $this->lastclearexpire = 0; } } function get($key){ global $timestamp; $ret = null; if($this->enable && ($key == 'ex_cache_keys' || (isset($this->keys[$key]) && (!$this->keys[$key] || $this->keys[$key] > $timestamp)))){ $ret = $this->obj->get($this->_key($key)); if(!is_array($ret)){ $ret = null; }else return $ret[0]; } return $ret; } function set($key, $value, $ttl = 0){ global $timestamp; $ret = null; if($this->enable){ if($ret = $this->obj->set($this->_key($key), array($value), $ttl)){ if($timestamp - $this->lastclearexpire > EX_CACHE_EXPIRE) $this->clearexpire(); $this->keys[$key] = $ttl ? $timestamp + $ttl : 0; $this->obj->set($this->_key('ex_cache_keys'),array($this->keys)); } } return $ret; } function clearexpire(){ global $timestamp; foreach ($this->keys as $k => $v){ if($v && $timestamp > $v){ $this->type == 'secache' && $this->obj->rm($this->_key($k)); unset($this->keys[$k]); } } $this->lastclearexpire = $timestamp + EX_CACHE_EXPIRE; $this->set('lastclearexpire',$timestamp); } function rm($key){ $ret = null; if($this->enable){ $ret = $this->obj->rm($this->_key($key)); if($ret){ unset($this->keys[$key]); $this->obj->set($this->_key('ex_cache_keys'), array($this->keys)); } } return $ret; } function clear(){ if($this->enable && is_array($this->keys)){ $this->keys['ex_cache_keys'] = 0; foreach ($this->keys as $k => $v){ $this->obj->rm($this->_key($k)); } } $this->keys = array(); return true; } function _key($str){ global $excache_prefix; return (empty($excache_prefix) ? substr(md5($_SERVER['HTTP_HOST']),0,6).'_' : $excache_prefix).$str; } } class ex_memcache{ var $enable; var $obj; function ex_memcache(){ } function init($cfg){ if(!empty($cfg['server'])){ $this->obj = new Memcache; $connect = $cfg['pconnect'] ? @$this->obj->pconnect($cfg['server'],$cfg['port'],$cfg['timeout']) : @$this->obj->connect($cfg['server'],$cfg['port'],$cfg['timeout']); $this->enable = $connect ? true : false; } } function get($key) { return $this->obj->get($key); } function set($key, $value, $ttl = 0) { return $this->obj->set($key, $value, MEMCACHE_COMPRESSED, $ttl); } function rm($key) { return $this->obj->delete($key); } } class ex_eaccelerator{ function ex_eaccelerator(){ } function init($cfg = array()){ } function get($key){ return eaccelerator_get($key); } function set($key, $value, $ttl = 0){ return eaccelerator_put($key, $value, $ttl); } function rm($key){ return eaccelerator_rm($key); } } class ex_xcache{ function ex_xcache(){ } function init($cfg = array()){ } function get($key){ return xcache_get($key); } function set($key, $value, $ttl = 0) { return xcache_set($key, $value, $ttl); } function rm($key) { return xcache_unset($key); } } class ex_secache{ var $enable; var $obj; function ex_secache(){ } function init($cfg) { if(!empty($cfg['size']) && !empty($cfg['datafile'])){ define('SECACHE_SIZE',$cfg['size'].'M'); require(M_ROOT."include/secache.cls.php"); $this->obj = new secache; $this->obj->workat($cfg['datafile']); $this->enable = true; } } function get($key){ return $this->obj->fetch($this->_key($key),$value) ? $value : false; } function set($key, $value, $ttl = 0){ return $this->obj->store($this->_key($key),$value); } function rm($key){ return $this->obj->delete($this->_key($key)); } function _key($str){ return md5($str); } }