Description

colesbury

opened on Dec 1, 2023

Issue body actions

Bug report

The _PySemaphore_PlatformWait function in parking_lot.c has three implementations:

• WaitForSingleObjectEx (for Windows)
• sem_timedwait (Linux and most other POSIX platforms)
• pthread_cond_timedwait (macOS and possibly other platforms that don't have sem_timedwait)

We should follow the pattern used in thread_pthread.h where we prefer functions that support CLOCK_MONOTONIC. These are sem_clockwait and pthread_cond_timedwait after setting pthread_condattr_setclock.

Additionally, we should use _PyTime_AsTimespec_clamp instead of _PyTime_AsTimespec (we don't want to raise errors in these code paths).

Note that:

1. Windows doesn't need any changes because WaitForSingleObjectEx isn't relative to any specific clock -- it just takes a timeout for N milliseconds in the future
2. macOS doesn't support pthread_condattr_setclock, so we're stuck with the system clock on macOS. It's not clear to me if we use the pthread_cond_timedwait for any other OS.

Linked PRs

• gh-112606: Use monotonic clock when supported in semaphore waiting in parking_lot.c #112614
• gh-112606: Use pthread_cond_timedwait_relative_np in parking_lot.c when available #112616
• gh-112606: Use sem_clockwait with monotonic time when supported in parking_lot.c #112733

Activity

1. colesbury

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   3.13only security fixesonly security fixes

   topic-free-threading

   on Dec 1, 2023
2. mattprodani commented on Dec 4, 2023

   

   mattprodani

   on Dec 4, 2023

   Contributor

   More actions

   Splitting into two PRs for sem_timedwait and pthread_cond_timedwait implementations. Working on finishing up the condvar implementation to share fields that initialize the proper pthread_condattr_t from thread_pthread.h as per notes.

   • gh-112606: Use sem_clockwait with monotonic time when supported in parking_lot.c #112733
   • gh-112606: Use pthread_cond_timedwait_relative_np in parking_lot.c when available #112616
3. colesbury

   assigned

   mattprodani

   on Dec 5, 2023
4. corona10

   added a commit that references this issue on Dec 6, 2023

   gh-112606: Use sem_clockwait with monotonic time when supported in pa…

   a2a46f9
5. vstinner commented on Dec 6, 2023

   

   vstinner

   on Dec 6, 2023

   Member

   More actions

   As someone writes a fix for the mutex, ping me, I can review it ;-)
6. erlend-aasland

   added a commit that references this issue on Jan 30, 2024

   gh-112606: Use pthread_cond_timedwait_relative_np() in parking_lot.c …

   e5e1866
7. aisk

   added 2 commits that reference this issue on Feb 11, 2024

   pythongh-112606: Use sem_clockwait with monotonic time when supported…

   141cdf4

   pythongh-112606: Use pthread_cond_timedwait_relative_np() in parking_…

   646d2d1
8. Glyphack

   added a commit that references this issue on Sep 2, 2024

   pythongh-112606: Use sem_clockwait with monotonic time when supported…

   de99b75
9. colesbury commented on Oct 8, 2024

   

   colesbury

   on Oct 8, 2024

   ContributorAuthor

   More actions

   Closing this as the relevant PRs landed a while ago.
10. colesbury

    closed this as completedon Oct 8, 2024

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