JL空间

if u don't know what cache_lite, please google it.

cache_lite source code(we can use it out of this class)

cache_lite
Cache_lite//getOption
clean//clean cache
extendLife//extend the life of avalid cache file
get//if cache is available return it
getMemoryCachingState//load the state of the caching memory array from a given file cache
lastModified//return the cache last modification time
raiseError//trigger a pear error
remove//remove a cache file
save//save some data in a cache file
saveMemoryCachingState//save the state of the caching memory array into a cache file cache
setLifeTime//set a new life time
setOption//generic way to set a cache_lite option
setToDebug//when an error is found, the script will stop and the message will be displayed(in debug mode)


we can find import function: getMemoryCachingState, saveMemoryState, save, get.

getMemoryCachingState, saveMemoeyState means what? php can define memory space like c? no.
let's see its source code.

    function saveMemoryCachingState($id, $group = 'default')
    {
        if ($this->_caching) {
            $array = array(
                'counter' => $this->_memoryCachingCounter,
                'array' => $this->_memoryCachingState
            );
            $data = serialize($array);
            $this->save($data, $id, $group);
        }
    }
    function save($data, $id = NULL, $group = 'default')
    {
        if ($this->_caching) {
            if ($this->_automaticSerialization) {
                $data = serialize($data);
            }
            if (isset($id)) {
                $this->_setFileName($id, $group);
            }
            if ($this->_memoryCaching) {
                $this->_memoryCacheAdd($data);
                if ($this->_onlyMemoryCaching) {
                    return true;
                }
            }
            if ($this->_automaticCleaningFactor>0) {
                $rand = rand(1, $this->_automaticCleaningFactor);
                if ($rand==1) {
                    $this->clean(false, 'old');
                }
            }
            if ($this->_writeControl) {
                $res = $this->_writeAndControl($data);
                if (is_bool($res)) {
                    if ($res) {
                        return true;  
                    }
                    // if $res if false, we need to invalidate the cache
                    @touch($this->_file, time() - 2*abs($this->_lifeTime));
                    return false;
                }            
            } else {
                $res = $this->_write($data);
            }
            if (is_object($res)) {
        // $res is a PEAR_Error object 
                if (!($this->_errorHandlingAPIBreak)) {   
                return false; // we return false (old API)
            }
        }
            return $res;
        }
        return false;
    }
    function _memoryCacheAdd($data)
    {
        [B]$this->_memoryCachingArray[$this->_file] = $data;[/B]
        if ($this->_memoryCachingCounter >= $this->_memoryCachingLimit) {
            list($key, ) = each($this->_memoryCachingArray);
            unset($this->_memoryCachingArray[$key]);
        } else {
            $this->_memoryCachingCounter = $this->_memoryCachingCounter + 1;
        }
    }

we can find it use array like global array, memoryCache is just Cache_lite public array.


we must know hash(google "data structures") when we analyze set, get function.

    function _write($data)
    {
        if ($this->_hashedDirectoryLevel > 0) {
            $hash = md5($this->_fileName);
            $root = $this->_cacheDir;
            for ($i=0 ; $i<$this->_hashedDirectoryLevel ; $i++) {
                $root = $root . 'cache_' . substr($hash, 0, $i + 1) . '/';
                if (!(@is_dir($root))) {
                    @mkdir($root, $this->_hashedDirectoryUmask);
                }
            }
        }
        $fp = @fopen($this->_file, "wb");
        if ($fp) {
            if ($this->_fileLocking) @flock($fp, LOCK_EX);
            if ($this->_readControl) {
                @fwrite($fp, $this->_hash($data, $this->_readControlType), 32);
            }
            $len = strlen($data);
            @fwrite($fp, $data, $len);
            if ($this->_fileLocking) @flock($fp, LOCK_UN);
            @fclose($fp);
            return true;
        }      
        return $this->raiseError('Cache_Lite : Unable to write cache file : '.$this->_file, -1);
    }

cache_lite use some string(hash string) to set directory when use hashedDirectoryLevel(u can find it in cache_lite document) .

if we know how to store it, and it is easy how to get it.

    function _read()
    {
        $fp = @fopen($this->_file, "rb");
        if ($this->_fileLocking) @flock($fp, LOCK_SH);
        if ($fp) {
            clearstatcache();
            $length = @filesize($this->_file);
            $mqr = get_magic_quotes_runtime();
            set_magic_quotes_runtime(0);
            if ($this->_readControl) {
                $hashControl = @fread($fp, 32);
                $length = $length - 32;
            } 
            if ($length) {
                $data = @fread($fp, $length);
            } else {
                $data = '';
            }
            set_magic_quotes_runtime($mqr);
            if ($this->_fileLocking) @flock($fp, LOCK_UN);
            @fclose($fp);
            if ($this->_readControl) {
                $hashData = $this->_hash($data, $this->_readControlType);
                if ($hashData != $hashControl) {
                    if (!(is_null($this->_lifeTime))) {
                        @touch($this->_file, time() - 2*abs($this->_lifeTime)); 
                    } else {
                        @unlink($this->_file);
                    }
                    return false;
                }
            }
            return $data;
        }
        return $this->raiseError('Cache_Lite : Unable to read cache !', -2); 
    }

Cache_lite is a small file cache, and it only fit for small system, test system and only php system.

Memcached is a high-performance, distributed memory object caching system。
It fit for any system, and it not only fit for php system.


Write by JL
2007-2-21