regrtest: don't fail immediately if a child does crash

[vstinner]

BPO	29362
Nosy	@vstinner, @ammaraskar
Files	regrtest_crash.diff regrtest_crashed.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-02-06.13:13:02.298>
created_at = <Date 2017-01-24.15:35:21.698>
labels = ['3.7', 'type-feature', 'tests']
title = "regrtest: don't fail immediately if a child does crash"
updated_at = <Date 2017-02-06.13:13:02.297>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2017-02-06.13:13:02.297>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-02-06.13:13:02.298>
closer = 'vstinner'
components = ['Tests']
creation = <Date 2017-01-24.15:35:21.698>
creator = 'vstinner'
dependencies = []
files = ['46446', '46480']
hgrepos = []
issue_num = 29362
keywords = ['patch']
message_count = 7.0
messages = ['286194', '286195', '286419', '286639', '287122', '287123', '287124']
nosy_count = 3.0
nosy_names = ['vstinner', 'python-dev', 'ammar2']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29362'
versions = ['Python 3.7']

[vstinner]

When regrtest is used with -jN, regrtest spawn child processes to run tests. If a child crashs, regrtest master process immedialtely fails. It would prefer to be able to continue to run following tests. It's not because a single test crashed that all tests would crash.

Example of output when a crash occurs:
-----------------
(...)
0:02:45 [118/404/3] test_bytes crashed -- running: test_multiprocessing_spawn (67 sec), test_io (54 sec), test_subprocess (76 sec)
python: Objects/abstract.c:2186: _Py_CheckFunctionResult: Assertion `(callable != NULL) ^ (where != NULL)' failed.
Fatal Python error: Aborted

Current thread 0x00007f9210f11440 (most recent call first):
File "/home/haypo/prog/python/git_cpython/Lib/unittest/case.py", line 177 in handle
File "/home/haypo/prog/python/git_cpython/Lib/unittest/case.py", line 728 in assertRaises
File "/home/haypo/prog/python/git_cpython/Lib/test/test_bytes.py", line 636 in test_maketrans
(...)
File "/home/haypo/prog/python/git_cpython/Lib/runpy.py", line 85 in _run_code
File "/home/haypo/prog/python/git_cpython/Lib/runpy.py", line 193 in _run_module_as_main

Traceback (most recent call last):
  File "/home/haypo/prog/python/git_cpython/Lib/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  (...)
  File "/home/haypo/prog/python/git_cpython/Lib/test/libregrtest/main.py", line 411, in run_tests
    run_tests_multiprocess(self)
  File "/home/haypo/prog/python/git_cpython/Lib/test/libregrtest/runtest_mp.py", line 221, in run_tests_multiprocess
    raise Exception(msg)
Exception: Child error on test_bytes: Exit code -6

---

[vstinner]

At least, I would like to see which tests were executed, which tests failed, total duration, etc. Get a summary!

[ammaraskar]

This patch makes it so that when a child runner crashes during a multiprocess test run, it is treated similar to a keyboard interrupt. That is, the currently running tests will continue to run and immediately after it will print out a summary.

I think the test suite should be interrupted when an interpreter crash happens because this indicates a fairly major failure and interrupting the suite brings a lot of attention to it.

[vstinner]

Attached patch changes libregrtest to handle CHILD_ERROR as a normal result and continue the execution of following tests. As a result, it displays the test summary as usual on such crash.

--

Ammar Askar: Thanks for regrtest_crash.diff, but I prefer to execute other unit tests rather than exiting immediatly.

The --failfast option can be used with my patch to exit at the first crash or failure (with my patch, a crash is handled as a test failure).

[python-dev]

New changeset 4446613000a3 by Victor Stinner in branch 'default':
regrtest: don't fail immediately if a child does crash
https://hg.python.org/cpython/rev/4446613000a3

[python-dev]

New changeset 99e4e687145a76ac28055a651ee31470496c3ac7 by Victor Stinner in branch 'master':
regrtest: don't fail immediately if a child does crash
99e4e68

[vstinner]

I fixed regrtest in Python 3.7. Maybe I will backport the fix later to other branches, but I prefer to limit regrtest changes in stable branches.