Steps to reproduce:

- clone pytest-cov at https://bitbucket.org/schlamar/pytest-cov/commits/ac14225a67d715b6649f8158e05d2389b78620d2
- remove `@pytest.mark.skipif` from `test_multiprocessing_subprocess` in test_pytest_cov.py
- run: `tox --develop -e py27 -- -x`

Result: it fails with MemoryError in `subprocess._args_from_interpreter_flags` because sys.flags.hash_randomization has a value of 2147483647 and it tries to build a string with such a length. Find more details in attached log. Patch is following.

Patch added.

This comes from http://bugs.python.org/issue12098. Python 3.3 is affected, too.

Reproduction can be minimized by running the following script:


import multiprocessing


def main():
    p = multiprocessing.Process(target=lambda: None)
    p.start()
    p.join()


if __name__ == '__main__':
    main()

as

$ PYTHONHASHSEED=2147483647 python test.py
Traceback (most recent call last):
  File "test.py", line 12, in <module>
    main()
  File "test.py", line 7, in main
    p.start()
  File "c:\Python27\lib\multiprocessing\process.py", line 130, in start
    self._popen = Popen(self)
  File "c:\Python27\lib\multiprocessing\forking.py", line 258, in __init__
    cmd = get_command_line() + [rhandle]
  File "c:\Python27\lib\multiprocessing\forking.py", line 364, in get_command_line
    opts = util._args_from_interpreter_flags()
  File "c:\Python27\lib\subprocess.py", line 508, in _args_from_interpreter_flags
    args.append('-' + opt * v)
MemoryError

Added TestCase.

BTW, patches are for 2.7 branch.

Merged test case and fix in a single commit/patch.

This was fixed in #19284 for Python 3.4 (without having possible consequences in mind). I have updated my patch accordingly.

Maybe it's worth to port my test case to Python 3.4.

Removed Python 3.3 as it isn't in bugfix maintenance anymore.

Just got hit with this in 2.7.

FWIW, I've been using a this patch for 2.7.5 in a production setting for a month now and have had no problems.

The fix for Lib/subprocess.py looks good to me, but the test doesn't fail without the fix, so the test doesn't look good to me:

$ ./python -m test.regrtest -v test_multiprocessing_subprocess

At least, the test doesn't ensure that the bug is fixed.

New changeset d42f6ce08362 by Gregory P. Smith in branch '2.7':
Fixes issue #20954: _args_from_interpreter_flags used by multiprocessing
https://hg.python.org/cpython/rev/d42f6ce08362

_args_from_interpreter_flags really deserves its own unittest using a stubbed out sys.flags.  if someone wants to go ahead with the test provided in the existing patch here or write one of those, feel free.

As is, i've committed a patch logically equivalent (but less hacky) to the one from #19284.  Ironically _that_ patch wasn't the right thing to do in python _3_ but that's a separate issue i'll address outside of this bug.  It is effective for Python 2 where hash randomization must be explicitly enabled.