How to restart swoole smoothly

swoole Smooth restart

In swoole, we can send various signals to the main process, and the main process will receive Different signal types are processed. For example, the following

SIGTERM, an elegant termination signal, will interrupt the process after it has finished executing the current program, instead of killing the process directly (recommended learning: swoole video tutorial)

SIGUSR1, will restart all Worker processes smoothly

SIGUSR2, will restart all Task processes smoothly

If we want to restart the server, we only need to send the SIGUSR1 signal to the main process.

The principle of smooth restart is that when the main process receives the SIGUSR1 signal, the main process will send a safe exit signal to a child process. The so-called safe exit means that the main process will not directly The Worker process is killed, but waits for the child process to finish processing the work at hand, then allows it to "retire" gloriously, and finally starts a new child process (reloading the new PHP program code).

Then send the "retirement" command to other child processes, thus restarting all child processes one after another.

We noticed that smooth restart actually means to let the old child processes exit one by one and re-create new processes. In order not to affect users during smooth restart, this requires that user-related status information not be saved in the process. That is, the business process should be stateless to avoid information loss due to process exit.

It feels very good. All you need to do to restart is to simply send a signal to the main process and that's it.

The ideal is very fulfilling, but the reality is not.

In swoole, restarting is only effective for files loaded after the Worker process is started! What does it mean? It means that restarting is only meaningful for files loaded after the onWorkerStart callback. If you want a file that has been loaded into memory before the Worker process is started to take effect again, you can only shut down the server and restart it.

Having said so much, let’s write an example to see how to send the SIGUSR1 signal to the main process to effectively restart the Worker process.

First we create a Test class to process the data of the onReceive callback. Why should we take out the onReceive callback business and write it separately? You will understand after reading the example.

<?php

class Test
{
    public function run($data)
    {
        echo $data;
    }
}

In the Test::run method, our first step is just to echo the data received by swoole_server.

We create a swoole_server class NoReload.php in the current directory

<?php
require_once("Test.php");
class NoReload
{
    private $_serv;
    private $_test;
    /**
     * init
     */
    public function __construct()
    {
        $this->_serv = new Swoole\Server("127.0.0.1", 9501);
        $this->_serv->set([
            &#39;worker_num&#39; => 1,
        ]);
        $this->_serv->on(&#39;Receive&#39;, [$this, &#39;onReceive&#39;]);
        $this->_test = new Test;
    }
    /**
     * start server
     */
    public function start()
    {
        $this->_serv->start();
    }
    public function onReceive($serv, $fd, $fromId, $data)
    {
        $this->_test->run($data);
    }
}
$noReload = new NoReload;
$noReload->start();

Special reminder: When we initialize swoole_server, the way we write it is the namespace way

new Swoole\Server

The writing method of this style is equivalent to the underline writing method. Swoole supports both writing styles.

new swoole_server

In addition, let’s take a look at the code logic of the server: before the class definition, require_once Test.php and initialize it. When setting up a Worker process, the NoReload::onReceive method was registered as the onReceive callback of swoole_server, and the data received in the onReceive callback was passed to the Test::run method for processing.

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