process.terminate() doesn't work for a chrome / firefox subprocess if a browser window is already present

Question

I am launching a sub-process using the following command:

p=subprocess.Popen(["google-chrome","--new-window","http://www.hckrnews.com"])

I need to kill this process after sometime, so I'm using:

time.sleep(t)
p.terminate()

This works only if no instance of the browser is already open. If a browser window is already present, a new window opens but does not terminate after specified time.

I also tried the method given in this question, but that also doesn't work in case of already present window.

score 6 · Accepted Answer · edited Apr 13 '17 at 12:22

This is not a python problem, and your code doesn't contain errors. It's a problem with the browsers. When you launch the firefox or chrome's executable with --new-window a new window is opened in the existing instance of the browser.

In other words the process you just started connects to the already existing process of firefox/chrome and instructs that process to open a new window and then terminates. So when you call terminate() nothing really happens because the process you started already ended.

You can check this with few lines of code:

>>> import subprocess
>>> p = subprocess.Popen(['firefox', '-new-window'])
>>> p.wait()   # uh-oh. this should be blocking!
0
>>> p.terminate()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/subprocess.py", line 1551, in terminate
    self.send_signal(signal.SIGTERM)
  File "/usr/lib/python2.7/subprocess.py", line 1546, in send_signal
    os.kill(self.pid, sig)
OSError: [Errno 3] No such process

You should tell the browser to open a new instance instead of a new window. Firefox has a -new-instance option, even though, when trying to use it, the only thing I get is that a pop-up appears saying that I cannot open two instances of the browser. Whether opening multiple instances of a browser in a certain OS session is allowed depends on the browser and may not be possible.

On Chrome I believe you can open a new session telling Chrome to use a different directory to store its data (see here for example). No idea whether this is possible in firefox.

Thanks a lot! I'll try using Chrome with a different directory for user data. Also, it doesn't make sense that Firefox has a -new-instance option but doesn't allow to open multiple instances! — metanoia5, Sep 01 '14 at 15:24
@quasistatic : multiple instances are allowed, it's just that they must use different profiles. — mhawke, Sep 01 '14 at 15:33

score 3 · Answer 2 · edited May 23 '17 at 12:09

As explained in Bakuriu's answer, --new-window creates a new window, but under an existing instance of firefox, if there is one. If there is no existing instance, a new one is created.

It is possible to use -new-instance to tell Firefox to start a new instance for a different firefox user profile. The profile must already exist and this is limited to one instance per profile. A new profile can be created interactively with firefox -P -new-instance, and a new instance can then be started with firefox -P <profile_name> -new-instance. Mozilla's profile documentation is here.

It should be possible to programmatically create the profile - after all it is just a directory and an entry in the ~/.mozilla/profiles.ini file. Of course, this is for Firefox only, chrome might be completely different (or impossible?). An example:

import tempfile
import subprocess
import shutil
import time
import ConfigParser

MOZILLA_PROFILES_INI = '.mozilla/firefox/profiles.ini'
PROFILE_SECTION = 'Profile1'

URL = 'http://www.hckrnews.com'
profile_dir = tempfile.mkdtemp()

# quick and dirty add new profile to profiles.ini, or update if already present.
config = ConfigParser.SafeConfigParser()
config.optionxform = str         # preserve case of option names
config.read(MOZILLA_PROFILES_INI)
try:
    config.add_section(PROFILE_SECTION)
except ConfigParser.DuplicateSectionError, exc:
    pass

config.set(PROFILE_SECTION, 'Name', 'temp_profile')
config.set(PROFILE_SECTION, 'IsRelative', '0')
config.set(PROFILE_SECTION, 'Path', profile_dir)

# write out config with hack to remove added spaces around '=' - more care needed here as it just overwrites the global mozilla config!
class NoSpaceWriter(file):
    def write(self, s):
        super(NoSpaceWriter, self).write(s.replace(' = ', '='))

with NoSpaceWriter(MOZILLA_PROFILES_INI, 'w') as profiles_ini:
   config.write(profiles_ini)

p = subprocess.Popen(['firefox', '-P', 'temp_profile', '-new-instance', URL])
time.sleep(10)
p.terminate()

shutil.rmtree(profile_dir, True)

process.terminate() doesn't work for a chrome / firefox subprocess if a browser window is already present

2 Answers2