| msg235637 - (view) |
Author: STINNER Victor (vstinner) *  |
Date: 2015-02-09 21:34 |
| Python 3.5 now requires a monotonic clock to start and has the C function _PyTime_monotonic(). Python/condvar.h and Python/thread_pthread.h should use the monotonic clock CLOCK_MONOTONIC, not the system clock CLOCK_REALTIME. See the PEP 418 for the rationale. Most platforms support pthread_condattr_setclock(CLOCK_MONOTONIC), except Mac OS X and old versions of Android. The glib looks to use pthread_cond_timedwait_relative_np() for Mac OS X: https://mail.gnome.org/archives/commits-list/2014-February/msg07782.html Note: Android had non-standard pthread_cond_timedwait_monotonic() and pthread_cond_timedwait_monotonic_np() functions. Android is not a official supported platform, and newer Android version now support pthread_condattr_setclock(). I prefer to not support old Android versions (yet). https://android-review.googlesource.com/#/c/83881/ -- For Windows, SleepConditionVariableSRW() is used on Windows 7 and newer, otherwise WaitForSingleObjectEx() is used. By the way, the check looks to be done during the compilation. I should check which Windows version is used to build Python... SleepConditionVariableSRW() and WaitForSingleObjectEx() both take a relative timeout, so they don't use (directly) the system clock. I don't see any required change for Windows. According to the PEP 418: "WaitForSingleObject() uses the same timer as GetTickCount() with the same precision." Hum, it is not possible to interrupt such wait() with CTRL+c? time.sleep() is implemented with WaitForSingleObjectEx() with _PyOS_SigintEvent(). It doesn't look to be the case here. |
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| msg235639 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2015-02-09 22:12 |
| > Python/condvar.h and Python/thread_pthread.h should use the monotonic clock CLOCK_MONOTONIC Oh, I forgot that Python/thread_pthread.h only uses pthread_cond_timedwait() if semaphores are emulated with mutexes+conditional variables. On most platforms, PyThread_acquire_lock_timed() is implemented with sem_timedwait(). Problem: sem_timedwait() requires an absolute time using the CLOCK_REALTIME clock and the clock is not yet configurable on Linux :-( See the feature request in the glibc: "Bug 14717 - Allow choice of clock source for calls to sem_timedwait() and pthread_mutex_timedwait()" opened in 2012: https://sourceware.org/bugzilla/show_bug.cgi?id=14717 Note: QNX provides sem_timedwait_monotonic(). |
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| msg235640 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2015-02-09 22:17 |
| cond_timedwait_monotonic.patch: Work-in-progress patch. It doesn't change configure.ac yet to check if pthread_condattr_setclock() is supported (with CLOCK_MONOTONIC). |
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| msg236156 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2015-02-17 23:47 |
| Oh, I missed the issue #12822 which looks to fix similar bugs. |
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| msg273565 - (view) |
Author: Charalampos Stratakis (cstratak) * |
Date: 2016-08-24 14:17 |
| Hello, Is there any progress on the issue? Should someone take over? |
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| msg333841 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2019-01-17 10:05 |
| I marked bpo-31267 "threading.Timer object is affected by changes to system time: Python locks should use a monotonic clock if available" as a duplicate of this issue. |
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| msg333844 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2019-01-17 10:07 |
| I closed bpo-35747 "Python threading event wait influenced by date change" as a duplicate of the issue. |
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| msg333845 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2019-01-17 10:11 |
| > Is there any progress on the issue? Should someone take over? It's a limitation of the libc, not directly of Python. The problem is that the sem_timedwait() function of the glibc doesn't allow to specify which clock is used: https://sourceware.org/bugzilla/show_bug.cgi?id=14717 Someone has to contribute to the glibc to add an option to sem_init() or sem_timedwait() to allow to use a different clock than CLOCK_REALTIME. One workaround is to use Python to use the mutex+cond implementation of pthread locks, since this one is already able to use CLOCK_MONOTONIC: https://bugs.python.org/issue31267#msg302257 |
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| msg333846 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2019-01-17 10:11 |
| See also bpo-12822: "NewGIL should use CLOCK_MONOTONIC if possible". |
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| msg333851 - (view) |
Author: Pablo Galindo Salgado (pablogsal) * |
Date: 2019-01-17 10:57 |
| > One workaround is to use Python to use the mutex+cond implementation of pthread locks, since this one is already able to use CLOCK_MONOTONIC: Does this have any drawbacks? |
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| msg336060 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2019-02-20 10:35 |
| INADA-san fixed bpo-12822 with: New changeset 001fee14e0f2ba5f41fb733adc69d5965925a094 by Inada Naoki in branch 'master': bpo-12822: use monotonic clock for condvar if possible (GH-11723) https://github.com/python/cpython/commit/001fee14e0f2ba5f41fb733adc69d5965925a094 |
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| msg376341 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2020-09-04 08:50 |
| See bpo-41710 "Timeout is affected by jumps in system time". |
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