protected function spawnInitialWorkers()
    {
        $this->logger->debug('spawn initial ['.$this->min_children.'] workers', [
            'category' => get_class($this),
        ]);

        if (self::PM_DYNAMIC === $this->pm || self::PM_STATIC === $this->pm) {
            for ($i = $this->count(); $i < $this->min_children; ++$i) {
                $this->spawnWorker();
            }
        }
    }