think\Process::getPid PHP Method

    public function getPid()
    {
        if ($this->isSigchildEnabled()) {
            throw new \RuntimeException('This PHP has been compiled with --enable-sigchild. The process identifier can not be retrieved.');
        }
        $this->updateStatus(false);
        return $this->isRunning() ? $this->processInformation['pid'] : null;
    }