通过 Python 使用 Selenium 进行多处理时，Chrome 在几

问题描述

这是几个小时抓取后的错误回溯:

This is the error traceback after several hours of scraping:

The process started from chrome location /usr/bin/google-chrome is no longer running, so ChromeDriver is assuming that Chrome has crashed.

这是我的 selenium python 设置:

This is my setup of selenium python:

#scrape.py
from selenium.common.exceptions import *
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.chrome.options import Options

def run_scrape(link):
    chrome_options = Options()
    chrome_options.add_argument('--no-sandbox')
    chrome_options.add_argument("--headless")
    chrome_options.add_argument('--disable-dev-shm-usage')
    chrome_options.add_argument("--lang=en")
    chrome_options.add_argument("--start-maximized")
    chrome_options.add_experimental_option("excludeSwitches", ["enable-automation"])
    chrome_options.add_experimental_option('useAutomationExtension', False)
    chrome_options.add_argument("user-agent=Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36")
    chrome_options.binary_location = "/usr/bin/google-chrome"
    browser = webdriver.Chrome(executable_path=r'/usr/local/bin/chromedriver', options=chrome_options)
    browser.get(<link passed here>)
    try:
        #scrape process
    except:
        #other stuffs
    browser.quit()

#multiprocess.py
import time,
from multiprocessing import Pool
from scrape import *

if __name__ == '__main__':
    start_time = time.time()
    #links = list of links to be scraped
    pool = Pool(20)
    results = pool.map(run_scrape, links)
    pool.close()
    print("Total Time Processed: "+"--- %s seconds ---" % (time.time() - start_time))

Chrome、ChromeDriver 设置、Selenium 版本

Chrome, ChromeDriver Setup, Selenium Version

ChromeDriver 79.0.3945.36 (3582db32b33893869b8c1339e8f4d9ed1816f143-refs/branch-heads/3945@{#614})
Google Chrome 79.0.3945.79
Selenium Version: 4.0.0a3

我想知道为什么 chrome 正在关闭但其他进程正在运行?

Im wondering why is the chrome is closing but other processes are working?

推荐答案

我拿了你的代码，稍微修改了一下以适应我的测试环境，下面是执行结果:

I took your code, modified it a bit to suit to my Test Environment and here is the execution results:

• 代码块:

• Code Block:

• multiprocess.py:

import time
from multiprocessing import Pool
from multiprocessingPool.scrape import run_scrape

if __name__ == '__main__':
    start_time = time.time()
    links = ["https://selenium.dev/downloads/", "https://selenium.dev/documentation/en/"] 
    pool = Pool(2)
    results = pool.map(run_scrape, links)
    pool.close()
    print("Total Time Processed: "+"--- %s seconds ---" % (time.time() - start_time)) 

from selenium import webdriver
from selenium.common.exceptions import NoSuchElementException, TimeoutException
from selenium.webdriver.common.by import By
from selenium.webdriver.chrome.options import Options

def run_scrape(link):
    chrome_options = Options()
    chrome_options.add_argument('--no-sandbox')
    chrome_options.add_argument("--headless")
    chrome_options.add_argument('--disable-dev-shm-usage')
    chrome_options.add_argument("--lang=en")
    chrome_options.add_argument("--start-maximized")
    chrome_options.add_experimental_option("excludeSwitches", ["enable-automation"])
    chrome_options.add_experimental_option('useAutomationExtension', False)
    chrome_options.add_argument("user-agent=Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36")
    chrome_options.binary_location=r'C:Program Files (x86)GoogleChromeApplicationchrome.exe'
    browser = webdriver.Chrome(executable_path=r'C:UtilityBrowserDriverschromedriver.exe', options=chrome_options)
    browser.get(link)
    try:
        print(browser.title)
    except (NoSuchElementException, TimeoutException):
        print("Error")
    browser.quit()

控制台输出:

Downloads
The Selenium Browser Automation Project :: Documentation for Selenium
Total Time Processed: --- 10.248600006103516 seconds ---

很明显你的程序在逻辑上完美无缺.

It is pretty much evident your program is logically flawless and just perfect.

正如您在几个小时的抓取后提到的这个错误，我怀疑这是因为 WebDriver 不是线程安全的.话虽如此，如果您可以序列化对底层驱动程序实例的访问，则可以在多个线程中共享一个引用.这是不可取的.但是你总是可以实例化一个 WebDriver 每个线程的实例.

As you mentioned this error surfaces after several hours of scraping, I suspect this due to the fact that WebDriver is not thread-safe. Having said that, if you can serialize access to the underlying driver instance, you can share a reference in more than one thread. This is not advisable. But you can always instantiate one WebDriver instance for each thread.

理想情况下，线程安全的问题不在于您的代码，而在于实际的浏览器绑定.他们都假设一次只有一个命令(例如，像真实用户一样).但另一方面，您始终可以为每个将启动多个浏览选项卡/窗口的线程实例化一个 WebDriver 实例.到目前为止，您的程序似乎很完美.

Ideally the issue of thread-safety isn't in your code but in the actual browser bindings. They all assume there will only be one command at a time (e.g. like a real user). But on the other hand you can always instantiate one WebDriver instance for each thread which will launch multiple browsing tabs/windows. Till this point it seems your program is perfect.

现在，不同的线程 可以在同一个Webdriver 上运行，但是测试的结果不会是你所期望的.背后的原因是，当您使用多线程在不同的选项卡/窗口上运行不同的测试时，需要一点线程安全编码，否则您将执行的操作如 click() 或 send_keys() 将转到当前具有焦点 的打开的选项卡/窗口，而不管您希望运行的线程.这实质上意味着所有测试将在具有焦点但不在预期选项卡/窗口上的同一选项卡/窗口上同时运行.

Now, different threads can be run on same Webdriver, but then the results of the tests would not be what you expect. The reason behind is, when you use multi-threading to run different tests on different tabs/windows a little bit of thread safety coding is required or else the actions you will perform like click() or send_keys() will go to the opened tab/window that is currently having the focus regardless of the thread you expect to be running. Which essentially means all the test will run simultaneously on the same tab/window that has focus but not on the intended tab/window.

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