Correct reuse argument tuple in property descriptor

[serhiy-storchaka]

BPO	24276
Nosy	@warsaw, @rhettinger, @ericvsmith, @ericsnowcurrently, @serhiy-storchaka, @llllllllll
Files	property_cached_args.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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-05-24.20:32:03.648>
created_at = <Date 2015-05-24.13:11:49.739>
labels = ['interpreter-core', 'type-crash']
title = 'Correct reuse argument tuple in property descriptor'
updated_at = <Date 2015-05-24.20:32:03.648>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-05-24.20:32:03.648>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-05-24.20:32:03.648>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2015-05-24.13:11:49.739>
creator = 'serhiy.storchaka'
dependencies = []
files = ['39482']
hgrepos = []
issue_num = 24276
keywords = ['patch']
message_count = 5.0
messages = ['243980', '243983', '243992', '243993', '243998']
nosy_count = 7.0
nosy_names = ['barry', 'rhettinger', 'eric.smith', 'python-dev', 'eric.snow', 'serhiy.storchaka', 'llllllllll']
pr_nums = []
priority = 'high'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue24276'
versions = ['Python 3.5']

[serhiy-storchaka]

Property descriptor getter uses cached tuple for args (bpo-23910). This can cause problems when called function use args after reading other property or save args. For now I know only one example - clru_cache_3.patch in bpo-14373.

Proposed patch use cached tuple in more robust manner.

[serhiy-storchaka]

Affect on performance:

$ ./python -m timeit -r 11 -s "from collections import namedtuple as n;a = n('n', 'a b c')(1, 2, 3)"

Unpatched: 10000000 loops, best of 11: 0.0567 usec per loop
Patched : 10000000 loops, best of 11: 0.0567 usec per loop

[rhettinger]

LGTM, go ahead and apply.

[serhiy-storchaka]

Sorry, it was incorrect microbenchmark. Correct is:

$ ./python -m timeit -r 11 -s "from collections import namedtuple as n;a = n('n', 'a b c')(1, 2, 3)" -- "a.a"
3.4          : 1000000 loops, best of 11: 0.601 usec per loop
3.5 unpatched: 1000000 loops, best of 11: 0.445 usec per loop
3.5 patched  : 1000000 loops, best of 11: 0.454 usec per loop

There is small slowdown (2%), but it is only small part of the gain of the optimization.

[python-dev]

New changeset 5dbf3d932a59 by Serhiy Storchaka in branch 'default':
Issue bpo-24276: Fixed optimization of property descriptor getter.
https://hg.python.org/cpython/rev/5dbf3d932a59