Chain reloading or non-stop service reloading.

[mt3925]

Here is the code for the current graceful restart:
code

    def restart_all(self) -> None:
        for idx, process in enumerate(self.processes):
            process.terminate()
            process.join()
            new_process = Process(self.config, self.target, self.sockets)
            new_process.start()
            self.processes[idx] = new_process

Since using spawn mode to create a new process will be slower to start a new process, so after all the old processes are killed, there will be no new process to serve for a few seconds, if we start a new process and then wait for that process to become available before killing the old process, we can achieve a chained restart without interrupting service.