[2.7] valgrind python2 -m test.regrtest test___all__: definitely lost: 324 bytes in 2 blocks

[vstinner]

BPO	37329
Nosy	@vstinner, @methane, @serhiy-storchaka
PRs	[2.7] bpo-37329: valgrind: ignore _PyWarnings_Init false alarms #14202

^{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 2019-06-28.16:16:40.512>
created_at = <Date 2019-06-18.13:05:21.191>
labels = ['extension-modules', 'performance']
title = '[2.7] valgrind python2 -m test.regrtest test___all__: definitely lost: 324 bytes in 2 blocks'
updated_at = <Date 2019-06-28.16:16:40.509>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2019-06-28.16:16:40.509>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-28.16:16:40.512>
closer = 'vstinner'
components = ['Extension Modules']
creation = <Date 2019-06-18.13:05:21.191>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 37329
keywords = ['patch']
message_count = 5.0
messages = ['345985', '345986', '345987', '346829', '346830']
nosy_count = 3.0
nosy_names = ['vstinner', 'methane', 'serhiy.storchaka']
pr_nums = ['14202']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue37329'
versions = ['Python 2.7']

[vstinner]

$ ./configure -C --enable-unicode=ucs4 --with-valgrind
$ make
$ valgrind --suppressions=Misc/valgrind-python.supp ./python -m test.regrtest test___all__
(...)
==18497== LEAK SUMMARY:
==18497==    definitely lost: 324 bytes in 2 blocks
==18497==    indirectly lost: 0 bytes in 0 blocks
==18497==      possibly lost: 5,665,418 bytes in 27,453 blocks
==18497==    still reachable: 8,530,840 bytes in 57,856 blocks
==18497==         suppressed: 32 bytes in 1 blocks
==18497== Reachable blocks (those to which a pointer was found) are not shown.
==18497== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==18497== 
==18497== For lists of detected and suppressed errors, rerun with: -s
==18497== ERROR SUMMARY: 4082 errors from 4082 contexts (suppressed: 0 from 0)

I'm concerned by "324 bytes in 2 blocks". Attached PR fix it.

Downstream issue: https://bugzilla.redhat.com/show_bug.cgi?id=1696322

Fixing "definitely lost" false alarm should help to catch real memory leaks.

[vstinner]

The best would be to explicitly release all memory at exit, but I don't think that it's worth it in Python 2.7 since this version is now stable. More work in done in the master branch to cleanup things at exit (ex: bpo-36724).

[vstinner]

The best would be to explicitly release all memory at exit, but I don't think that it's worth it in Python 2.7 (...)

Python 2.7 "leaks" a lot of memory at exit...

==18497== possibly lost: 5,665,418 bytes in 27,453 blocks
==18497== still reachable: 8,530,840 bytes in 57,856 blocks

... but the operating system releases the memory anyway when the process exit. Technically, it's not a major issue unless you embed Python into an application. But again, it's Python 2.7: I suggest to focus efforts in the master branch.

[vstinner]

New changeset 065aff3 by Victor Stinner in branch '2.7':
[2.7] bpo-37329: valgrind: ignore _PyWarnings_Init false alarms (GH-14202)
065aff3

[vstinner]

I confirm that my fix works with this manual test. I get "definitely lost: 0 bytes in 0 blocks" as expected:

$ valgrind --suppressions=Misc/valgrind-python.supp ./python -m test.regrtest test___all__
(...)
==23782== LEAK SUMMARY:
==23782==    definitely lost: 0 bytes in 0 blocks
==23782==    indirectly lost: 0 bytes in 0 blocks
==23782==      possibly lost: 17,945,740 bytes in 85,380 blocks
==23782==    still reachable: 283,821 bytes in 475 blocks
==23782==         suppressed: 2,605 bytes in 20 blocks
==23782== Reachable blocks (those to which a pointer was found) are not shown.