Swoole implements a highly reliable publish and subscribe system

With the development of the Internet, more and more applications need to implement real-time push and subscription of messages. This requires a highly reliable publish and subscribe system to support this demand. Swoole, as a high-performance network communication framework, can well meet this demand.

Swoole is an extension module of the PHP language, which can provide asynchronous, parallel, high-performance network communication and multi-process concurrent processing capabilities. Applications developed based on Swoole can support higher concurrency and shorter response time. In this article, we will introduce how to use Swoole to implement a highly reliable publish and subscribe system.

1. Basic concepts of publish-subscribe system

The publish-subscribe system is a messaging model that supports one-to-many message publishing and subscription. The publisher publishes messages to one or more topics, and subscribers can subscribe to these topics according to their own interests to receive corresponding messages.

Publish and subscribe systems usually consist of three parts: publishers, subscribers and message brokers (Message Broker). Publishers send messages to message brokers, and subscribers subscribe to messages from message brokers. Publishers and subscribers do not communicate directly. The message broker is responsible for routing messages to the corresponding subscribers.

2. The basic concepts of Swoole

Before understanding Swoole to implement the publish and subscribe system, we need to understand some basic concepts of Swoole.

1. Process

In Swoole, a process refers to an independent execution environment. Swoole provides multi-process support and can achieve concurrent processing by creating multiple processes.

2. Server

The server is the core module of the Swoole framework and can create a TCP or UDP server. When the server starts, it will create a main process and multiple sub-processes. The main process is responsible for listening on the port, and the sub-processes handle specific requests.

3. Timer

Swoole provides a timer function that can execute a piece of code within a specified time interval. Timers can be used in scenarios such as scheduled tasks and scheduled checks.

4. Coroutine

Coroutine is a lightweight thread that can run multiple coroutines simultaneously in one thread. Coroutines can implement asynchronous programming and avoid the overhead of thread switching in traditional multi-threaded programming. Swoole provides support for coroutines, which can be used to implement high-concurrency network programming.

3. Steps for Swoole to implement a publish and subscribe system

Next we will introduce how to use Swoole to implement a publish and subscribe system. In order to reduce the code complexity, we will use active polling by subscribers to implement the subscription function.

1. Create a message agent

First we need to create a message agent, which is responsible for receiving messages and routing them to the corresponding subscribers. We can use the TCP server and process management functions provided by Swoole to implement message brokers.

$server = new SwooleServer('0.0.0.0', 8080, SWOOLE_PROCESS);
$server->set([
    'worker_num' => 2,
    'daemonize' => false,
]);
$server->on('WorkerStart', function($serv, $worker_id) {
    // 创建消息队列
    $queue_key = ftok(__FILE__, 'a');
    $queue = msg_get_queue($queue_key, 0666 | IPC_CREAT);
    // 将消息队列作为全局变量存放起来
    global $message_queue;
    $message_queue = $queue;
    // 启动消息处理进程
    if ($worker_id == 0) {
        $process = new SwooleProcess(function($process) {
            global $message_queue;
            while (true) {
                // 从消息队列中获取消息
                if (msg_receive($message_queue, 0, $msg_type, 1024, $msg, true, MSG_IPC_NOWAIT)) {
                    // 将消息发送给对应的订阅者
                    // TODO:实现发送消息的逻辑
                }
                // 隔一段时间循环一次
                usleep(100);
            }
        }, false, false);
        $process->start();
    }
});
$server->on('Connect', function($serv, $fd) {
    echo "Client[$fd]: Connect.
";
});
$server->on('Receive', function($serv, $fd, $from_id, $data) {
    global $message_queue;
    // 接收到消息，将消息存放到消息队列
    if (msg_send($message_queue, 1, $data, true, true)) {
        echo "Received message: $data
";
    } else {
        echo "Failed to send message to message queue.
";
    }
});
$server->on('Close', function($serv, $fd) {
    echo "Client[$fd]: Close.
";
});
$server->start();

In the above code, we created a TCP server and set up 2 child processes. When each child process starts, we create a message queue and store it in the global variable $message_queue. In the first sub-process, we create a message processing process, which will get the message from the message queue and send the message to the corresponding subscriber. When receiving a message, we store the message in the message queue through the msg_send function.

2. Implementing the subscription function

The subscription function means that subscribers can choose the topics they need to subscribe to according to their own interests, thereby receiving relevant messages. We can implement the subscription function through Swoole's coroutine.

$client = new SwooleClient(SWOOLE_SOCK_TCP);
if (!$client->connect('127.0.0.1', 8080)) {
    echo "Failed to connect to server.
";
    exit(1);
}
// 订阅主题
if (!$client->send("subscribe:topic1")) {
    echo "Failed to send subscribe message.
";
    exit(1);
}
// 接收消息
while (true) {
    $data = $client->recv();
    if ($data === false) {
        echo "Failed to receive message.
";
        break;
    }
    if (empty($data)) {
        continue;
    }
    echo "Received message: $data
";
}
$client->close();

In the above code, we create a TCP client and connect to the port of the message broker. Subscription messages are sent through the send function, and the subscription topic is topic1. When receiving a message, we use a loop to check if there is a new message, and use the recv function to block and wait for new messages.

3. Implement the publishing function

The publishing function means that the publisher can publish messages to the specified topic. We can use Swoole's TCP client to implement the publishing function.

$client = new SwooleClient(SWOOLE_SOCK_TCP);
if (!$client->connect('127.0.0.1', 8080)) {
    echo "Failed to connect to server.
";
    exit(1);
}
// 发布消息
if (!$client->send("publish:topic1:message1")) {
    echo "Failed to send publish message.
";
    exit(1);
}
$client->close();

In the above code, we create a TCP client and connect to the port of the message broker. Publish messages through the send function. The publishing topic is topic1 and the message content is message1.

4. Summary

Swoole is a powerful network programming framework that can help us implement high-performance, high-concurrency network applications. This article introduces how to use Swoole to implement a highly reliable publish and subscribe system, which mainly includes creating a message agent, implementing subscription functions and publishing functions. Using Swoole to implement a publish and subscribe system can improve the performance and reliability of the system and is suitable for various application scenarios that require messaging functions.

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