编辑一个多线程爬虫编码的框架

以下是一个多线程爬虫编码的框架：

import threading
import queue
import requests
from bs4 import BeautifulSoup

class Crawler:
    def __init__(self, start_url, num_threads):
        self.start_url = start_url
        self.num_threads = num_threads
        self.queue = queue.Queue()
        self.visited = set()
        self.lock = threading.Lock()

    def enqueue(self, url):
        self.queue.put(url)

    def dequeue(self):
        return self.queue.get()

    def is_visited(self, url):
        with self.lock:
            if url in self.visited:
                return True
            else:
                self.visited.add(url)
                return False

    def crawl(self):
        self.enqueue(self.start_url)
        for i in range(self.num_threads):
            t = threading.Thread(target=self.worker)
            t.daemon = True
            t.start()

        self.queue.join()

    def worker(self):
        while True:
            url = self.dequeue()
            if self.is_visited(url):
                continue
            print("Crawling: " + url)
            try:
                response = requests.get(url)
                soup = BeautifulSoup(response.content, "html.parser")
                # process the page here
                # ...
                # add links to the queue
                for link in soup.find_all("a"):
                    self.enqueue(link.get("href"))
            except Exception as e:
                print("Error: " + str(e))

if __name__ == "__main__":
    crawler = Crawler("https://www.example.com", 10)
    crawler.crawl()

这个框架使用了一个队列来存储待处理的链接，并且使用一个集合来存储已经访问过的链接。当一个链接被取出时，会首先检查它是否已经被访问过。如果已经被访问过，则跳过这个链接。否则，将其标记为已访问，并进行爬取。爬取完成后，会从页面中提取所有链接，并将它们添加到队列中等待处理。这个框架使用多个线程来并行处理链接，可以加快爬取速度。