code: def wait_for_port_open(self, postmaster, timeout):
          
          for _ in polling_loop(timeout):
              with self._cancellable_lock:
                  if self._is_cancelled:
                      return False
  
              if not postmaster.is_running():
                  logger.error('postmaster is not running')
                  self.set_state('start failed')
                  return False
  
              isready = self.pg_isready()
              if isready != STATE_NO_RESPONSE:
                  if isready not in [STATE_REJECT, STATE_RUNNING]:
                      logger.warning("Can't determine PostgreSQL startup status, assuming running")
                  return True
  
          logger.warning("Timed out waiting for PostgreSQL to start")
          return False
docs: Waits until PostgreSQL opens ports.