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Unnecessary Cache of Shared Object Handles #88061

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insertinterestingnamehere mannequin opened this issue Apr 20, 2021 · 4 comments
Closed

Unnecessary Cache of Shared Object Handles #88061

insertinterestingnamehere mannequin opened this issue Apr 20, 2021 · 4 comments
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@gpshead
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3.11 only security fixes

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Mannequin

BPO 43895
Nosy @Yhg1s, @brettcannon, @gpshead, @ncoghlan, @ericsnowcurrently, @insertinterestingnamehere
PRs
  • bpo-43895: Remove an unnecessary cache of shared object handles #25487
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    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/gpshead'
closed_at = <Date 2021-07-07.23:26:50.342>
created_at = <Date 2021-04-20.17:00:51.537>
labels = ['3.11']
title = 'Unnecessary Cache of Shared Object Handles'
updated_at = <Date 2021-07-07.23:26:50.341>
user = 'https://github.com/insertinterestingnamehere'

    bugs.python.org fields:

    activity = <Date 2021-07-07.23:26:50.341>
actor = 'gregory.p.smith'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2021-07-07.23:26:50.342>
closer = 'gregory.p.smith'
components = []
creation = <Date 2021-04-20.17:00:51.537>
creator = 'Ian.H'
dependencies = []
files = []
hgrepos = []
issue_num = 43895
keywords = ['patch']
message_count = 4.0
messages = ['391453', '391454', '397122', '397123']
nosy_count = 6.0
nosy_names = ['twouters', 'brett.cannon', 'gregory.p.smith', 'ncoghlan', 'eric.snow', 'Ian.H']
pr_nums = ['25487']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue43895'
versions = ['Python 3.11']
    @insertinterestingnamehere
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    While working on another project I noticed that there's a cache of shared object handles kept inside _PyImport_FindSharedFuncptr. See

    cpython/Python/dynload_shlib.c

    Lines 51 to 55 in b2b6cd0

    static struct {
    dev_t dev;
    ino_t ino;
    void *handle;
    } handles[128];
    . It appears to be an optimization to work around poor caching of shared object handles in old libc implementations. After some testing, I have been unable to find any meaningful performance difference from this cache, so I propose we remove it to save the space.

    My initial tests were on Linux (Ubuntu 18.04). I saw no discernible difference in the time for running the Python test suite with a single thread. Running the test suite using a single thread shows a lot of variance, but after running with and without the cache 40 times the mean times with/without the cache was nearly the same. Interpreter startup time also appears to be unaffected. This was all with a debug build, so I'm in the process of collecting data with a release build to see if that changes anything.

    @insertinterestingnamehere insertinterestingnamehere mannequin added 3.10 only security fixes labels Apr 20, 2021
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    Proposed patch is in #25487.

    @gpshead gpshead added the 3.11 only security fixes label Jul 6, 2021
    @gpshead gpshead self-assigned this Jul 6, 2021
    @gpshead gpshead added the 3.11 only security fixes label Jul 6, 2021
    @gpshead gpshead self-assigned this Jul 6, 2021
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    gpshead commented Jul 7, 2021

    New changeset fed2fc4 by Ian Henriksen in branch 'main':
    bpo-43895: Remove an unnecessary cache of shared object handles (GH-25487)
    fed2fc4

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    gpshead commented Jul 7, 2021

    Thanks Ian!

    @gpshead gpshead removed the 3.10 only security fixes label Jul 7, 2021
    @gpshead gpshead closed this as completed Jul 7, 2021
    @gpshead gpshead removed the 3.10 only security fixes label Jul 7, 2021
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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