Object/provider/FileSystemCache.php
protected function accessible($id)
    {
        return $this->exist($id) && $this->readable($id) && $this->writable($id);
    }
protected function accessible($id)
    {
        return $this->exist($id) && $this->readable($id) && $this->writable($id);
    }
Accessible

Check if a cache id is
accessible

@param string $id - the cache id

@return boolean - the accessibility state