https://github.com/python/cpython/commit/badd5d5ceb25aed7a402a30e265b653920e0dd40 commit: badd5d5ceb25aed7a402a30e265b653920e0dd40 branch: main author: Zanie Blue <[email protected]> committer: itamaro <[email protected]> date: 2026-10-23T00:32:56Z summary:
gh-160368: Detect `sem_clockwait` at runtime on Linux (#160371) When Python is built with older Linux libc headers, timed semaphore waits use the real-time clock even if `sem_clockwait` is available at runtime. Use a weak reference on supported compilers to select `sem_clockwait` at runtime, falling back to `sem_timedwait` when the symbol is absent. ThreadSanitizer builds continue to use the real-time clock. Addresses [astral-sh/python-build-standalone#1176](https://github.com/astral-sh/python-build-standalone/issues/1176). files: A Misc/NEWS.d/next/Core_and_Builtins/2026-10-21-18-00-00.gh-issue-160368.sem-clockwait.rst M Python/parking_lot.c diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-21-18-00-00.gh-issue-160368.sem-clockwait.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-21-18-00-00.gh-issue-160368.sem-clockwait.rst new file mode 100644 index 00000000000000..11d7467b38413a --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-21-18-00-00.gh-issue-160368.sem-clockwait.rst @@ -0,0 +1,3 @@ +On Linux, allow timed semaphore waits to use the monotonic clock when +``sem_clockwait`` is available at runtime, even if Python was built with +older libc headers. diff --git a/Python/parking_lot.c b/Python/parking_lot.c index 8823d77719cb9a..8431b9bb24ec44 100644 --- a/Python/parking_lot.c +++ b/Python/parking_lot.c @@ -10,6 +10,18 @@ #include <stdbool.h> +#if defined(_Py_USE_SEMAPHORES) && defined(CLOCK_MONOTONIC) && !defined(_Py_THREAD_SANITIZER) +# ifdef HAVE_SEM_CLOCKWAIT +# define _Py_SEM_CLOCKWAIT_AVAILABLE 1 +# elif defined(__linux__) && (defined(__GNUC__) || defined(__clang__)) +/* Older glibc headers do not declare sem_clockwait. A weak reference allows + such builds to use monotonic waits on newer runtimes. */ +extern int sem_clockwait(sem_t *, clockid_t, const struct timespec *) + __attribute__((weak)); +# define _Py_SEM_CLOCKWAIT_AVAILABLE (sem_clockwait != NULL) +# endif +#endif + typedef struct { // The mutex protects the waiter queue and the num_waiters counter. @@ -151,24 +163,27 @@ _PySemaphore_Wait(_PySemaphore *sema, PyTime_t timeout) if (timeout >= 0) { struct timespec ts; -#if defined(CLOCK_MONOTONIC) && defined(HAVE_SEM_CLOCKWAIT) && !defined(_Py_THREAD_SANITIZER) - PyTime_t now; - // silently ignore error: cannot report error to the caller - (void)PyTime_MonotonicRaw(&now); - PyTime_t deadline = _PyTime_Add(now, timeout); - _PyTime_AsTimespec_clamp(deadline, &ts); - - err = sem_clockwait(&sema->platform_sem, CLOCK_MONOTONIC, &ts); -#else - PyTime_t now; - // silently ignore error: cannot report error to the caller - (void)PyTime_TimeRaw(&now); - PyTime_t deadline = _PyTime_Add(now, timeout); - - _PyTime_AsTimespec_clamp(deadline, &ts); +#ifdef _Py_SEM_CLOCKWAIT_AVAILABLE + if (_Py_SEM_CLOCKWAIT_AVAILABLE) { + PyTime_t now; + // Silently ignore error: cannot report error to the caller. + (void)PyTime_MonotonicRaw(&now); + PyTime_t deadline = _PyTime_Add(now, timeout); + _PyTime_AsTimespec_clamp(deadline, &ts); - err = sem_timedwait(&sema->platform_sem, &ts); + err = sem_clockwait(&sema->platform_sem, CLOCK_MONOTONIC, &ts); + } + else #endif + { + PyTime_t now; + // Silently ignore error: cannot report error to the caller. + (void)PyTime_TimeRaw(&now); + PyTime_t deadline = _PyTime_Add(now, timeout); + _PyTime_AsTimespec_clamp(deadline, &ts); + + err = sem_timedwait(&sema->platform_sem, &ts); + } } else { err = sem_wait(&sema->platform_sem); _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
