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threading.Condition.wait(timeout) should use a monotonic clock: use pthread_condattr_setclock(CLOCK_MONOTONIC) #57031

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threading.Condition.wait(timeout) should use a monotonic clock: use pthread_condattr_setclock(CLOCK_MONOTONIC)#57031
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3.8 (EOL)end of lifeinterpreter-core(Objects, Python, Grammar, and Parser dirs)type-bugAn unexpected behavior, bug, or error

Description

@methane
methane
opened on Aug 23, 2011
BPO 12822
Nosy @malemburg, @pitrou, @vstinner, @methane
PRs
  • bpo-12822: use monotonic clock for condvar if possible #11723
  • bpo-12822: use monotonic clock for condvar if possible #11723
    		•
    Files
  • use_monotonic_clock.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 2019-02-20.01:00:28.338>
created_at = <Date 2011-08-23.07:43:36.382>
labels = ['interpreter-core', 'type-bug', '3.8']
title = 'threading.Condition.wait(timeout) should use a monotonic clock: use pthread_condattr_setclock(CLOCK_MONOTONIC)'
updated_at = <Date 2021-10-01.08:52:42.541>
user = 'https://github.com/methane'

    bugs.python.org fields:

    activity = <Date 2021-10-01.08:52:42.541>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-02-20.01:00:28.338>
closer = 'methane'
components = ['Interpreter Core']
creation = <Date 2011-08-23.07:43:36.382>
creator = 'methane'
dependencies = []
files = ['23013']
hgrepos = []
issue_num = 12822
keywords = ['patch']
message_count = 13.0
messages = ['142789', '142791', '142856', '142858', '142859', '148525', '148528', '148529', '155837', '334621', '334623', '336032', '336061']
nosy_count = 5.0
nosy_names = ['lemburg', 'pitrou', 'vstinner', 'methane', 'neologix']
pr_nums = ['11723', '11723']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue12822'
versions = ['Python 3.8']

    Activity

    1. methane commented on Aug 23, 2011

      @methane
      methane
      on Aug 23, 2011
      MemberAuthor

      Using CLOCK_MONOTONIC is better than CLOCK_REALTIME (default) for GIL
      because settimeofday() may break the pthread_cond_timedwait().

      Attached patch uses CLOCK_MONOTONIC and clock_gettime. But I don't know
      how to write appropriate configure script.
      "-lrt" is also needed to use clock_gettime() but I don't know how to add
      it to LIBS.

    2. methane
      added
      type-bugAn unexpected behavior, bug, or error
      on Aug 23, 2011

    3. vstinner commented on Aug 23, 2011

      @vstinner
      vstinner
      on Aug 23, 2011
      Member

      See also bpo-10278.

    4. neologix commented on Aug 23, 2011

      @neologix
      neologixmannequin
      on Aug 23, 2011
      Mannequin

      Using CLOCK_MONOTONIC is better than CLOCK_REALTIME (default) for GIL
      because settimeofday() may break the pthread_cond_timedwait().

      Indeed.
      A couple remarks:

      • regular locks and conditions variables exposed by the threading module suffer from the same problem
      • POSIX semaphores are also affected, but you can't select an alternative clock source
      • actually, CLOCK_MONOTONIC is affected by NTP adjustements: while it's guaranteed not to go backward, its rate can be affected

      Did you really encounter this problem, or is this just a theoretical concern?

    5. pitrou commented on Aug 23, 2011

      @pitrou
      pitrou
      on Aug 23, 2011
      Member

      The patch is ok on the principle, but we do need a check that CLOCK_MONOTONIC is supported at build time.

    6. malemburg commented on Aug 23, 2011

      @malemburg
      malemburg
      on Aug 23, 2011
      Member

      Antoine Pitrou wrote:

      The patch is ok on the principle, but we do need a check that CLOCK_MONOTONIC is supported at build time.

      I think we need both: a check at build time to avoid
      compiler errors and a check at runtime whether the deployment
      platform supports the clock, plus a fallback solution in case
      it is not available.

    7. vstinner commented on Nov 28, 2011

      @vstinner
      vstinner
      on Nov 28, 2011
      Member

      The patch is ok on the principle, but we do need a check
      that CLOCK_MONOTONIC is supported at build time.

      timemodule.c is now using "#ifdef CLOCK_MONOTONIC".

    8. pitrou commented on Nov 28, 2011

      @pitrou
      pitrou
      on Nov 28, 2011
      Member

      Marc-Andre is right, a runtime check is probably also needed.
      (for example with mismatching kernel/libc)

    9. vstinner commented on Nov 28, 2011

      @vstinner
      vstinner
      on Nov 28, 2011
      Member

      pthread_condattr_setclock() result should be checked.

      "The pthread_condattr_setclock() function may fail if:

      EINVAL The value specified by clock_id does not refer to a known clock, or is a CPU-time clock."

    10. vstinner commented on Mar 15, 2012

      @vstinner
      vstinner
      on Mar 15, 2012
      Member

      See also bpo-14222. Python 3.3 has a new time.steady() function.

    11. methane commented on Jan 31, 2019

      @methane
      methane
      on Jan 31, 2019
      MemberAuthor

      ref: https://bugs.chromium.org/p/webrtc/issues/detail?id=9269
      macOS and iOS don't support pthread_condattr_setclock yet.

    12. methane
      added
      interpreter-core(Objects, Python, Grammar, and Parser dirs)
      3.8 (EOL)end of life
      on Jan 31, 2019

    13. vstinner commented on Jan 31, 2019

      @vstinner
      vstinner
      on Jan 31, 2019
      Member

      See also bpo-23428: "Use the monotonic clock for thread conditions on POSIX platforms".

    14. methane commented on Feb 20, 2019

      @methane
      methane
      on Feb 20, 2019
      MemberAuthor

      New changeset 001fee1 by Inada Naoki in branch 'master':
      bpo-12822: use monotonic clock for condvar if possible (GH-11723)
      001fee1

    15. methane
      closed this as completedon Feb 20, 2019

    16. vstinner commented on Feb 20, 2019

      @vstinner
      vstinner
      on Feb 20, 2019
      Member

      Thanks INADA-san for fixing this old issue!

    17. vstinner
      changed the title [-]NewGIL should use CLOCK_MONOTONIC if possible.[/-] [+]threading.Condition.wait(timeout) should use a monotonic clock: use pthread_condattr_setclock(CLOCK_MONOTONIC)[/+] on Oct 1, 2021
    18. ezio-melotti
      transferred this issue fromon Apr 10, 2022
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