public function attach($file = __FILE__)
{
if (!file_exists($file)) {
$touch = touch($file);
if (!$touch) {
throw new \RuntimeException("file is not exists and it can not be created. file: {$file}");
}
}
$key = ftok($file, 'a');
$this->shm = shm_attach($key, $this->size);
//allocate shared memory
}