protected static function monitorWorkers()
    {
        self::$_status = self::STATUS_RUNNING;
        while (1) {
            // Calls signal handlers for pending signals.
            pcntl_signal_dispatch();
            // Suspends execution of the current process until a child has exited, or until a signal is delivered
            $status = 0;
            $pid    = pcntl_wait($status, WUNTRACED);
            // Calls signal handlers for pending signals again.
            pcntl_signal_dispatch();
            。。。。。
  }