Swoole Practice: How to use coroutines to build high-performance crawlers

With the popularity of the Internet, Web crawlers have become a very important tool, which can help us quickly crawl the data we need, thereby reducing the cost of data acquisition. Performance has always been an important consideration in crawler implementation. Swoole is a coroutine framework based on PHP, which can help us quickly build high-performance web crawlers. This article will introduce the application of Swoole coroutines in web crawlers and explain how to use Swoole to build high-performance web crawlers.

1. Introduction to Swoole coroutine

Before introducing Swoole coroutine, we need to first understand the concept of coroutine. Coroutine is a user-mode thread, also called micro-thread, which can avoid the overhead caused by thread creation and destruction. Coroutines can be regarded as a more lightweight thread. Multiple coroutines can be created within a process, and coroutines can be switched at any time to achieve concurrency effects.

Swoole is a network communication framework based on coroutines. It changes PHP's thread model to a coroutine model, which can avoid the cost of switching between processes. Under Swoole's coroutine model, a process can handle tens of thousands of concurrent requests at the same time, which can greatly improve the program's concurrent processing capabilities.

2. Application of Swoole coroutine in Web crawlers

In the implementation of Web crawlers, multi-threads or multi-processes are generally used to handle concurrent requests. However, this method has some disadvantages, such as the high overhead of creating and destroying threads or processes, switching between threads or processes will also bring overhead, and communication issues between threads or processes also need to be considered. The Swoole coroutine can solve these problems. Swoole coroutine can be used to easily implement high-performance web crawlers.

The main process of using Swoole coroutine to implement web crawler is as follows:

1. Define the URL list of crawled pages.
2. Use the http client of Swoole coroutine to send HTTP requests to obtain page data and parse the page data.
3. To process and store the parsed data, you can use database, Redis, etc. for storage.
4. Use the timer function of the Swoole coroutine to set the running time of the crawler, and stop running when it times out.

For specific implementation, please refer to the following crawler code:

<?php

use SwooleCoroutineHttpClient;

class Spider
{
    private $urls = array();
    private $queue;
    private $maxDepth = 3; // 最大爬取深度
    private $currDepth = 0; // 当前爬取深度
    private $startTime;
    private $endTime;
    private $concurrency = 10; // 并发数
    private $httpClient;

    public function __construct($urls)
    {
        $this->urls = $urls;
        $this->queue = new SplQueue();
        $this->httpClient = new Client('127.0.0.1', 80);
    }

    public function run()
    {
        $this->startTime = microtime(true);
        foreach ($this->urls as $url) {
            $this->queue->enqueue($url);
        }
        while (!$this->queue->isEmpty() && $this->currDepth <= $this->maxDepth) {
            $this->processUrls();
            $this->currDepth++;
        }
        $this->endTime = microtime(true);
        echo "爬取完成，用时：" . ($this->endTime - $this->startTime) . "s
";
    }

    private function processUrls()
    {
        $n = min($this->concurrency, $this->queue->count());
        $array = array();
        for ($i = 0; $i < $n; $i++) {
            $url = $this->queue->dequeue();
            $array[] = $this->httpClient->get($url);
        }
        // 等待所有请求结束
        foreach ($array as $httpResponse) {
            $html = $httpResponse->body;
            $this->parseHtml($html);
        }
    }

    private function parseHtml($html)
    {
        // 解析页面
        // ...
        // 处理并存储数据
        // ...
        // 将页面中的URL添加到队列中
        // ...
    }
}

In the above code, we use the Http Client of the Swoole coroutine to send HTTP requests, and use PHP to parse the page data. With the built-in DOMDocument class, the code for processing and storing data can be implemented according to actual business needs.

3. How to use Swoole to build a high-performance web crawler

1. Multi-process/multi-thread

Using multi-process/multi-thread method to achieve When web crawling, you need to pay attention to the overhead of process/thread context switching and communication issues between processes/threads. At the same time, due to the limitations of PHP itself, multi-core CPUs may not be fully utilized.

2. Swoole coroutine

Using Swoole coroutine can easily implement high-performance web crawlers, and can also avoid some problems of multi-process/multi-threading.

When using Swoole coroutine to implement a web crawler, you need to pay attention to the following points:

(1) Use coroutine to send HTTP requests.

(2) Use coroutine to parse page data.

(3) Use coroutine to process data.

(4) Use the timer function to set the running time of the crawler.

(5) Use queue to manage crawled URLs.

(6) Set the number of concurrency to improve the efficiency of the crawler.

4. Summary

This article introduces how to use Swoole coroutine to build a high-performance web crawler. Using Swoole coroutines can easily implement high-performance web crawlers, while also avoiding some problems with multi-threads/multi-processes. In actual applications, optimization can be carried out according to actual business needs, such as using cache or CDN to improve the efficiency of crawlers.

The above is the detailed content of Swoole Practice: How to use coroutines to build high-performance crawlers. For more information, please follow other related articles on the PHP Chinese website!