Beginner's Guide to PHP: Asynchronous Programming

PHP, as a popular scripting language, has always been one of the mainstream languages ​​​​for Web development. In web development, asynchronous programming is increasingly used in high-performance scenarios such as web crawlers, real-time chat, and long polling. This article will introduce the relevant knowledge of PHP asynchronous programming so that readers can master the basics of asynchronous programming and improve the performance of Web applications.

1. Introduction to asynchronous programming

Asynchronous programming means that when calling a time-consuming I/O operation, the program does not have to wait for the completion of the operation, but executes it after the operation is completed. The corresponding callback function. Compared with synchronous programming, asynchronous programming has better response speed and concurrency capabilities, and can better utilize I/O waiting time.

2. PHP asynchronous programming implementation methods

There are two main implementation methods of PHP asynchronous programming: multi-process and event-driven.

1. Multi-process

The implementation of multi-process is to create multiple processes in the program, and each process performs a separate task. New processes can be created in Unix/Linux systems through the fork() system call, and the PCNTL extension package provides many function libraries for controlling child processes, which can realize process creation, termination, synchronization and other processes.

Although multi-process programming is simple, there are still many problems, such as inter-process communication, abnormal exit of child processes, etc. In addition, multiple processes will consume a lot of system resources when creating a large number of child processes, resulting in high system load.

2. Event-driven

Event-driven is the mainstream implementation of asynchronous programming in PHP. In this mode, the program continuously listens for events and only executes the corresponding callback function when the custom event is triggered. The event-driven model allows multiple connections to share one thread and process, making better use of system resources.

Commonly used PHP event-driven models include Reactor model and coroutine model. The Reactor model is an asynchronous programming model based on the event loop mechanism. In React, event-loop is used to poll I/O events. Once an event is triggered, the corresponding callback function will be called. The coroutine model achieves the purpose of asynchronous programming by controlling the entry and exit of the coroutine function.

Currently, commonly used extensions in PHP asynchronous programming are:

• Swoole: Swoole is a high-performance network communication framework based on Event-loop and Coroutine, which can easily implement asynchronous TCP /UDP/WebSocket service.
• Workerman: Workerman is a fully asynchronous non-blocking PHP framework that supports WebSocket and TCP/UDP communication.

3. PHP asynchronous programming example

The following uses a simple example to introduce the use of PHP asynchronous programming.

In this example, we will use the Swoole extension to implement a simple TCP service. After turning on the TCP service, the client can connect to the server through the telnet tool and send messages to the server. After receiving the message, the server sends the message back to the client.

The following are relevant code examples:

<?php
$server = new swoole_server('127.0.0.1', 9501, SWOOLE_PROCESS, SWOOLE_SOCK_TCP);
$server->set([
    'worker_num' => 4,
    'daemonize'  => false,
]);
$server->on('connect', function ($server, $fd) {
    echo "Client {$fd}: Connect.
";
});
$server->on('receive', function ($server, $fd, $from_id, $data) {
    $server->send($fd, 'Receive: ' . $data);
});
$server->on('close', function ($server, $fd) {
    echo "Client {$fd}: Close.
";
});
echo "Server Start.
";
$server->start();

In the above code, we first created a Swoole service through the new swoole_server function, and set up 4 worker processes with an IP address of 127.0.0.1 , the port number is 9501. Next, we registered three callback functions, corresponding to the client's connection, reception and closing events respectively. When a client connects, we print out a Connect message; when the client sends data, we send the data back to the client; when the client closes the connection, we print out a Close message. Finally, we output a Server Start message to start the service.

4. Summary

Asynchronous programming is an important skill in PHP web development, which can improve the performance and concurrency of web applications. This article introduces the concept and implementation of PHP asynchronous programming, and gives a simple usage example. We hope that readers can learn about the use of asynchronous programming and improve their web development capabilities by studying this article.

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