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gh-112606: Use monotonic clock when supported in semaphore waiting in parking_lot.c #112614

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gh-112606: Use monotonic clock when supported in semaphore waiting in parking_lot.c #112614

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33 changes: 30 additions & 3 deletions Python/parking_lot.c
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,20 @@ static Bucket buckets[NUM_BUCKETS] = {
BUCKET_INIT(buckets, 256),
};

// macOS supports CLOCK_MONOTONIC, but not pthread_condattr_setclock
#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined(CLOCK_MONOTONIC) \
&& !defined(_Py_USE_SEMAPHORES)
#define CONDATTR_MONOTONIC
#endif

// Condattr for monotonic clock types
static pthread_condattr_t *condattr;
// NULL if monotonic clock is not supported
#if defined(CONDATTR_MONOTONIC)
pthread_condattr_init(condattr);
pthread_condattr_setclock(condattr, CLOCK_MONOTONIC);
#endif

void
_PySemaphore_Init(_PySemaphore *sema)
{
Expand All @@ -70,7 +84,7 @@ _PySemaphore_Init(_PySemaphore *sema)
if (pthread_mutex_init(&sema->mutex, NULL) != 0) {
Py_FatalError("parking_lot: pthread_mutex_init failed");
}
if (pthread_cond_init(&sema->cond, NULL)) {
if (pthread_cond_init(&sema->cond, condattr)) {
Py_FatalError("parking_lot: pthread_cond_init failed");
}
sema->counter = 0;
Expand Down Expand Up @@ -118,10 +132,18 @@ _PySemaphore_PlatformWait(_PySemaphore *sema, _PyTime_t timeout)
if (timeout >= 0) {
struct timespec ts;

#if defined(CLOCK_MONOTONIC)
_PyTime_t deadline = _PyTime_Add(_PyTime_GetMonotonicClock(), timeout);
_PyTime_AsTimespec_clamp(deadline, &ts);

err = sem_clockwait(&sema->platform_sem, CLOCK_MONOTONIC, &ts);
#else
// does not support CLOCK_MONOTONIC, use system clock
_PyTime_t deadline = _PyTime_Add(_PyTime_GetSystemClock(), timeout);
_PyTime_AsTimespec(deadline, &ts);
_PyTime_AsTimespec_clamp(deadline, &ts);

err = sem_timedwait(&sema->platform_sem, &ts);
#endif
}
else {
err = sem_wait(&sema->platform_sem);
Expand Down Expand Up @@ -150,8 +172,13 @@ _PySemaphore_PlatformWait(_PySemaphore *sema, _PyTime_t timeout)
if (timeout >= 0) {
struct timespec ts;

#if defined(CONDATTR_MONOTONIC)
_PyTime_t deadline = _PyTime_Add(_PyTime_GetMonotonicClock(), timeout);
_PyTime_AsTimespec_clamp(deadline, &ts);
#else
_PyTime_t deadline = _PyTime_Add(_PyTime_GetSystemClock(), timeout);
_PyTime_AsTimespec(deadline, &ts);
_PyTime_AsTimespec_clamp(deadline, &ts);
#endif

err = pthread_cond_timedwait(&sema->cond, &sema->mutex, &ts);
}
Expand Down