Avoid repeated hash calculation in C implementation of OrderedDict

[serhiy-storchaka]

BPO	25462
Nosy	@rhettinger, @ezio-melotti, @ericsnowcurrently, @serhiy-storchaka
Files	odict_knownhash.patch odict_knownhash_2.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 2015-11-13.13:21:03.744>
created_at = <Date 2015-10-22.18:15:07.317>
labels = ['expert-regex', 'type-feature']
title = 'Avoid repeated hash calculation in C implementation of OrderedDict'
updated_at = <Date 2015-11-13.13:21:16.246>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-11-13.13:21:16.246>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2015-11-13.13:21:03.744>
closer = 'serhiy.storchaka'
components = ['Regular Expressions']
creation = <Date 2015-10-22.18:15:07.317>
creator = 'serhiy.storchaka'
dependencies = []
files = ['40838', '40960']
hgrepos = []
issue_num = 25462
keywords = ['patch']
message_count = 6.0
messages = ['253343', '254182', '254294', '254296', '254603', '254604']
nosy_count = 6.0
nosy_names = ['rhettinger', 'ezio.melotti', 'mrabarnett', 'python-dev', 'eric.snow', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue25462'
versions = ['Python 3.5', 'Python 3.6']

[serhiy-storchaka]

There are private _PyDict_*_KnownHash functions that allow to avoid repeated hash calculation in complex operations with a dict. Proposed patch makes C implementation of OrderedDict to use these functions. It is not just an optimization, it makes some OrderedDict methods atomic (or almost atomic), that decreases a chance to desynchronize the linked list with the dict. That is why I suggest to commit the patch in 3.5.

[serhiy-storchaka]

Could you please make a review of this patch Eric? It is moved to separate issue because it is enough large and complex.

[rhettinger]

The patch looks correct, and it improves the integrity of the C implementation.

[ericsnowcurrently]

I agree with Raymond.

[python-dev]

New changeset 52ff0c00a404 by Serhiy Storchaka in branch '3.5':
Issue bpo-25462: The hash of the key now is calculated only once in most
https://hg.python.org/cpython/rev/52ff0c00a404

New changeset 828c9b920532 by Serhiy Storchaka in branch 'default':
Issue bpo-25462: The hash of the key now is calculated only once in most
https://hg.python.org/cpython/rev/828c9b920532

[serhiy-storchaka]

Thank you Raymond and Eric.