CStatePersister

protected function getContent($filename)
{
    $file=@fopen($filename,"r");
    if($file && flock($file,LOCK_SH))
    {
        $contents=@file_get_contents($filename);
        flock($file,LOCK_UN);
        fclose($file);
        return $contents;
    }
    return false;
}

public function init()
{
    parent::init();
    if($this->stateFile===null)
        $this->stateFile=Yii::app()->getRuntimePath().DIRECTORY_SEPARATOR.'state.bin';
    $dir=dirname($this->stateFile);
    if(!is_dir($dir) || !is_writable($dir))
        throw new CException(Yii::t('yii','Unable to create application state file "{file}". Make sure the directory containing the file exists and is writable by the Web server process.',
            array('{file}'=>$this->stateFile)));
}

public function load()
{
    $stateFile=$this->stateFile;
    if($this->cacheID!==false && ($cache=Yii::app()->getComponent($this->cacheID))!==null)
    {
        $cacheKey='Yii.CStatePersister.'.$stateFile;
        if(($value=$cache->get($cacheKey))!==false)
            return unserialize($value);
        else
        {
            if(($content=$this->getContent($stateFile))!==false)
            {
                $unserialized_content=unserialize($content);
                // If it can't be unserialized, don't cache it:
                if ($unserialized_content!==false || $content=="") 
                    $cache->set($cacheKey,$content,0,new CFileCacheDependency($stateFile));
                return $unserialized_content;
            }
            else
                return null;
        }
    }
    elseif(($content=$this->getContent($stateFile))!==false)
        return unserialize($content);
    else
        return null;
}

public function save($state)
{
    file_put_contents($this->stateFile,serialize($state),LOCK_EX);
}