ResourceWarning: unclosed socket upon driver crashes

🐛 Bug Report

When running tests in parallel with pytest-xdist Chromium webdriver creation occasionally crashes or holds up a thread indefinitely for varying reasons:

E                 File ".../selenium-test/lib/python3.8/site-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
E                   raise exception_class(message, screen, stacktrace)
E               selenium.common.exceptions.SessionNotCreatedException: Message: session not created
E               from disconnected: Unable to receive message from renderer
E                 (Session info: headless chrome=88.0.4324.182)

E                 File ".../selenium-test/lib/python3.8/site-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
E                   raise exception_class(message, screen, stacktrace)
E               selenium.common.exceptions.WebDriverException: Message: unknown error: Chrome failed to start: crashed.
E                 (unknown error: DevToolsActivePort file doesn't exist)
E                 (The process started from chrome location /snap/chromium/1497/usr/lib/chromium-browser/chrome is no longer running, so ChromeDriver is assuming that Chrome has crashed.)

I’ve been trying to work around it by just re-trying the creation, however, I’m also getting unclosed socket warnings every time there is a crash:

E               During handling of the above exception, another exception occurred:
E
E               Traceback (most recent call last):
E                 File "<frozen importlib._bootstrap_external>", line 580, in _compile_bytecode
E               ResourceWarning: unclosed <socket.socket fd=19, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('127.0.0.1', 35816), raddr=('127.0.0.1', 59245)>

To Reproduce

Create a pytest test case file called test_case.py:

from pytest import fixture, mark
from selenium import webdriver


@fixture
def browser():
    options = webdriver.ChromeOptions()
    options.add_argument('--headless')
    options.add_argument(f'--window-size=1000,500')
    driver = webdriver.Chrome(executable_path='/snap/bin/chromium.chromedriver', options=options)
    yield driver
    driver.close()


@mark.parametrize('index', list(range(50)))
def test_create(browser, index):
    print(browser)

Install the following requirements into a virtual environment:

pytest~=6.2.2
pytest-xdist[psutil]~=2.2.1
selenium~=3.141.0

Add the following to pyproject.toml:

[tool.pytest.ini_options]
filterwarnings = ['error']

Run pytest -n 8 a few times. Note that the errors appear only occasionally (in only a few percent of the cases), therefore you may need to change the number of parallel test runs (-n 8) or the number of tests (list(range(50))) to see it appear.

Expected behavior

A Chromium webdriver is created correctly 100% of the times, or, at least there is no unclosed socket warnings on failed webdriver creation.

Environment

OS: Ubuntu 20.04 Browser: Chromium Browser version: 88.0.4324.182 (installed via snap) Browser Driver version: chromium.chromedriver 88.0.4324.182 Language Bindings version: Python 3.141.0

[AutomatedTester]

Truthfully it’s hard to know if this is related or not.

If we can clean up the crashes and it still occurs please raise a bug and I will look into it.

I’ve not seen this issue before so think it’s unrelated to the Python bindings or pytest-dist but there appears to be a lot of noise we need to clear before we can go into it more On Mar 1, 2021, 10:45 AM +0000, Gergely Kalmár , wrote:

Hi @AutomatedTester, thank you very much for the insight! What about the unclosed socket issue though, is that also outside of Selenium’s control? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or unsubscribe.

[GergelyKalmar]

I’ve been able to create a simpler test case which shows the issue more clearly.

Here is the test case:

from selenium import webdriver

for i in range(50):
    print(f'*** Run {i}')
    options = webdriver.ChromeOptions()
    options.add_argument('--headless')
    driver = webdriver.Chrome(options=options)
    print(driver)
    driver.quit()

Run it as python3 -Wd -X tracemalloc=25 test_case.py.

Note that the unclosed socket warning does appear in some runs (in a quite flaky way).

Also note that when using driver = webdriver.Chrome(options=options, keep_alive=False) the issue appears every time. The problem seems to be similar to what has been discussed in https://github.com/SeleniumHQ/selenium/issues/6878 and is related to how urllib3.PoolManager instances are managed in the RemoteConnection class (they are not cleaned up properly). When applying this patch it seems to solve the issue when keep_alive=False is set.

This issue appears to be fixed in the current version of https://github.com/SeleniumHQ/selenium/blob/trunk/py/selenium/webdriver/remote/remote_connection.py, so perhaps this will be resolved in 4.0.