python - pyvirtualdisplay 在 Xvfb 上的工作剂量是多少，或者 pyvirtualdisplay 可以打开多少个 Xvfb？

Question

1. 我使用以下代码打开 saveral Xvfb 进行测试，但遇到了一些问题:
   A. Xvfb 的状态(代码后面)有的进程是 Z 或 SL，有的进程是 Z+ 或 SL+，但 python 进程正常进行剂量是什么意思？
   B. 请求时代码运行正常，但最后出现异常(跟随状态)。

代码

#!/usr/bin/env python3
# encoding: utf-8
import os
import time
import random
import multiprocessing
from pyvirtualdisplay import Display
from selenium import webdriver

def main():
    display = Display(visible=0, size=(800, 600))
    display.start()
    print(os.getpid())
    browser = webdriver.Firefox()
    #time.sleep(20)
    for j in range(30):
        browser.get('http://www.google.com')
        print(browser.title)
        time.sleep(1) # !!!!!! this is sleep time
    browser.quit()
    display.stop()

if __name__ == '__main__':
    tl = []
    for i in range(10):
        tl.append(multiprocessing.Process(target=main))
    start = time.time()
    for j in tl:
        j.start()
    for j in tl:
        j.join()
    print("end {}".format((time.time() - start)))

状态

root     18503  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18504  0.1  0.7 233684 57364 ?        Sl   13:40   0:22 Xvfb -br -nolisten tcp -screen 0 800x800x24 :1049
root     18506  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18508  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18509  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18514  0.0  0.5 221140 44736 ?        Sl   13:40   0:11 Xvfb -br -nolisten tcp -screen 0 800x800x24 :1052
root     18515  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18516  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18517  0.0  0.0      0     0 ?        Z    13:40   0:00 [Xvfb] <defunct>
root     18520  0.0  0.4 212832 36468 ?        Sl   13:40   0:04 Xvfb -br -nolisten tcp -screen 0 800x800x24 :1055

异常

Process Process-10:
Traceback (most recent call last):
  File "/usr/lib/python3.5/multiprocessing/process.py", line 249, in _bootstrap
    self.run()
  File "/usr/lib/python3.5/multiprocessing/process.py", line 93, in run
    self._target(*self._args, **self._kwargs)
  File "/root/PycharmProjects/MyShiYanLou/auto_/test_xvfb.py", line 27, in main
    browser.quit()
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/firefox/webdriver.py", line 183, in quit
    RemoteWebDriver.quit(self)
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webdriver.py", line 592, in quit
    self.execute(Command.QUIT)
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webdriver.py", line 297, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/errorhandler.py", line 194, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.WebDriverException: Message: Failed to decode response from marionette

Answer 1

您遇到的异常不是由于 pyvirtualdisplay 可以打开一定数量的 Xvfb 而引起的，而是由于 selenium 将在您打开的最后一个虚拟显示器中打开。

想象一下有两个进程A和B的情况

1. A 打开 Xvfb
2. B 打开 Xvfb
3. A 在 B(最后一个打开的)打开的虚拟显示器中打开 Webdriver
4. B关闭 Xvfb
5. A 尝试获取网页，但由于打开 webdriver 的 Xvfb 已关闭而失败

避免该错误的最佳方法是在运行多个进程之前打开一个 Xvfb:

代码

#!/usr/bin/env python3
# encoding: utf-8
import os
import time
import multiprocessing
from pyvirtualdisplay import Display
from selenium import webdriver

def main():
    print(os.getpid())
    browser = webdriver.Firefox()
    for j in range(30):
        browser.get('http://www.google.com')
        print(browser.title)
        time.sleep(1)  # !!!!!! this is sleep time
    browser.quit()


if __name__ == '__main__':
    display = Display(visible=0, size=(800, 600))
    display.start()

    tl = []
    for i in range(10):
        tl.append(multiprocessing.Process(target=main))
    start = time.time()
    for j in tl:
        j.start()
    for j in tl:
        j.join()

    display.stop()

    print("end {}".format((time.time() - start)))