bpo-37091: subprocess - Handle uncaught PermissionError in send_signal

[wesinator]

Encountered a condition where uncaught PermissionError caused a hang
running a subprocess command with sudo -u

Python 3.7.3
Ubuntu 18.10 Cosmic

Traceback (most recent call last):
  File "/usr/lib/python3.7/subprocess.py", line 474, in run
    stdout, stderr = process.communicate(input, timeout=timeout)
  File "/usr/lib/python3.7/subprocess.py", line 939, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
  File "/usr/lib/python3.7/subprocess.py", line 1707, in _communicate
    self.wait(timeout=self._remaining_time(endtime))
  File "/usr/lib/python3.7/subprocess.py", line 990, in wait
    return self._wait(timeout=timeout)
  File "/usr/lib/python3.7/subprocess.py", line 1616, in _wait
    raise TimeoutExpired(self.args, timeout)
subprocess.TimeoutExpired: Command '['sudo', '-u', 'chrome', '/snap/bin/chromium', '--headless', '--disable-gpu', '--hide-scrollbars', '--ignore-certificate-errors', '--enable-sandbox', '--incognito', '--mute-audio', '--disable-databases', '--enable-strict-powerful-feature-restrictions', '--no-pings', '--no-referrers', '--user-agent="Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; rv:11.0) like Gecko"', '--timeout=30000', '--window-size=1280,1000', '--screenshot=[REDACTED]_screenshot.png', 'https://[REDACTED]']' timed out after 59.9998986274004 seconds

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.7/subprocess.py", line 476, in run
    process.kill()
  File "/usr/lib/python3.7/subprocess.py", line 1756, in kill
    self.send_signal(signal.SIGKILL)
  File "/usr/lib/python3.7/subprocess.py", line 1746, in send_signal
    os.kill(self.pid, sig)
PermissionError: [Errno 1] Operation not permitted

see also xonsh/xonsh#2887 (comment)

https://bugs.python.org/issue37091

[gpshead]

Just surround the os.kill call with this. Also, please file a related https://bugs.python.org/ issue to track the bug.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

And if you don't make the requested changes, you will be put in the comfy chair!

[wesinator]

Hmm, this is still hanging with the patch:

Traceback (most recent call last):
  File "/usr/lib/python3.7/subprocess.py", line 474, in run
    stdout, stderr = process.communicate(input, timeout=timeout)
  File "/usr/lib/python3.7/subprocess.py", line 939, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
  File "/usr/lib/python3.7/subprocess.py", line 1707, in _communicate
    self.wait(timeout=self._remaining_time(endtime))
  File "/usr/lib/python3.7/subprocess.py", line 990, in wait
    return self._wait(timeout=timeout)
  File "/usr/lib/python3.7/subprocess.py", line 1616, in _wait
    raise TimeoutExpired(self.args, timeout)

the code has the following except blocks:

except subprocess.TimeoutExpired as e:
        try:
            print(e)
        except PermissionError:
            print(e)
# handle race condition hanging issue
except PermissionError:
    pass

[gpshead]

This PR would change the behavior of send_signal to hide errors from people. We don't want to do that.