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[3.9] bpo-41710: PyThread_acquire_lock_timed() uses sem_clockwait() (GH-28671) #28683

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Merged
merged 1 commit into from
Oct 1, 2021
Merged

[3.9] bpo-41710: PyThread_acquire_lock_timed() uses sem_clockwait() (GH-28671) #28683

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5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Library/2021-09-30-23-00-18.bpo-41710.svuloZ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
On Unix, if the ``sem_clockwait()`` function is available in the C library
(glibc 2.30 and newer), the :meth:`threading.Lock.acquire` method now uses the
monotonic clock (:data:`time.CLOCK_MONOTONIC`) for the timeout, rather than
using the system clock (:data:`time.CLOCK_REALTIME`), to not be affected by
system clock changes. Patch by Victor Stinner.
53 changes: 41 additions & 12 deletions Python/thread_pthread.h
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Expand Up @@ -89,12 +89,17 @@
* mutexes and condition variables:
*/
#if (defined(_POSIX_SEMAPHORES) && !defined(HAVE_BROKEN_POSIX_SEMAPHORES) && \
defined(HAVE_SEM_TIMEDWAIT))
(defined(HAVE_SEM_TIMEDWAIT) || defined(HAVE_SEM_CLOCKWAIT)))
# define USE_SEMAPHORES
#else
# undef USE_SEMAPHORES
#endif

#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
// monotonic is supported statically. It doesn't mean it works on runtime.
#define CONDATTR_MONOTONIC
#endif


/* On platforms that don't use standard POSIX threads pthread_sigmask()
* isn't present. DEC threads uses sigprocmask() instead as do most
Expand All @@ -120,16 +125,23 @@ do { \
ts.tv_nsec = tv.tv_usec * 1000; \
} while(0)

#if defined(CONDATTR_MONOTONIC) || defined(HAVE_SEM_CLOCKWAIT)
static void
monotonic_abs_timeout(long long us, struct timespec *abs)
{
clock_gettime(CLOCK_MONOTONIC, abs);
abs->tv_sec += us / 1000000;
abs->tv_nsec += (us % 1000000) * 1000;
abs->tv_sec += abs->tv_nsec / 1000000000;
abs->tv_nsec %= 1000000000;
}
#endif


/*
* pthread_cond support
*/

#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
// monotonic is supported statically. It doesn't mean it works on runtime.
#define CONDATTR_MONOTONIC
#endif

// NULL when pthread_condattr_setclock(CLOCK_MONOTONIC) is not supported.
static pthread_condattr_t *condattr_monotonic = NULL;

Expand All @@ -151,16 +163,13 @@ _PyThread_cond_init(PyCOND_T *cond)
return pthread_cond_init(cond, condattr_monotonic);
}


void
_PyThread_cond_after(long long us, struct timespec *abs)
{
#ifdef CONDATTR_MONOTONIC
if (condattr_monotonic) {
clock_gettime(CLOCK_MONOTONIC, abs);
abs->tv_sec += us / 1000000;
abs->tv_nsec += (us % 1000000) * 1000;
abs->tv_sec += abs->tv_nsec / 1000000000;
abs->tv_nsec %= 1000000000;
monotonic_abs_timeout(us, abs);
return;
}
#endif
Expand Down Expand Up @@ -431,7 +440,9 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
sem_t *thelock = (sem_t *)lock;
int status, error = 0;
struct timespec ts;
#ifndef HAVE_SEM_CLOCKWAIT
_PyTime_t deadline = 0;
#endif

(void) error; /* silence unused-but-set-variable warning */
dprintf(("PyThread_acquire_lock_timed(%p, %lld, %d) called\n",
Expand All @@ -442,6 +453,9 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
}

if (microseconds > 0) {
#ifdef HAVE_SEM_CLOCKWAIT
monotonic_abs_timeout(microseconds, &ts);
#else
MICROSECONDS_TO_TIMESPEC(microseconds, ts);

if (!intr_flag) {
Expand All @@ -450,11 +464,17 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
_PyTime_t timeout = _PyTime_FromNanoseconds(microseconds * 1000);
deadline = _PyTime_GetMonotonicClock() + timeout;
}
#endif
}

while (1) {
if (microseconds > 0) {
#ifdef HAVE_SEM_CLOCKWAIT
status = fix_status(sem_clockwait(thelock, CLOCK_MONOTONIC,
&ts));
#else
status = fix_status(sem_timedwait(thelock, &ts));
#endif
}
else if (microseconds == 0) {
status = fix_status(sem_trywait(thelock));
Expand All @@ -469,6 +489,9 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
break;
}

// sem_clockwait() uses an absolute timeout, there is no need
// to recompute the relative timeout.
#ifndef HAVE_SEM_CLOCKWAIT
if (microseconds > 0) {
/* wait interrupted by a signal (EINTR): recompute the timeout */
_PyTime_t dt = deadline - _PyTime_GetMonotonicClock();
Expand All @@ -490,13 +513,19 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
microseconds = 0;
}
}
#endif
}

/* Don't check the status if we're stopping because of an interrupt. */
if (!(intr_flag && status == EINTR)) {
if (microseconds > 0) {
if (status != ETIMEDOUT)
if (status != ETIMEDOUT) {
#ifdef HAVE_SEM_CLOCKWAIT
CHECK_STATUS("sem_clockwait");
#else
CHECK_STATUS("sem_timedwait");
#endif
}
}
else if (microseconds == 0) {
if (status != EAGAIN)
Expand Down
2 changes: 1 addition & 1 deletion configure
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Expand Up @@ -11723,7 +11723,7 @@ for ac_func in alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
posix_fallocate posix_fadvise posix_spawn posix_spawnp pread preadv preadv2 \
pthread_condattr_setclock pthread_init pthread_kill pwrite pwritev pwritev2 \
readlink readlinkat readv realpath renameat \
sem_open sem_timedwait sem_getvalue sem_unlink sendfile setegid seteuid \
sem_open sem_timedwait sem_clockwait sem_getvalue sem_unlink sendfile setegid seteuid \
setgid sethostname \
setlocale setregid setreuid setresuid setresgid setsid setpgid setpgrp setpriority setuid setvbuf \
sched_get_priority_max sched_setaffinity sched_setscheduler sched_setparam \
Expand Down
2 changes: 1 addition & 1 deletion configure.ac
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Expand Up @@ -3707,7 +3707,7 @@ AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
posix_fallocate posix_fadvise posix_spawn posix_spawnp pread preadv preadv2 \
pthread_condattr_setclock pthread_init pthread_kill pwrite pwritev pwritev2 \
readlink readlinkat readv realpath renameat \
sem_open sem_timedwait sem_getvalue sem_unlink sendfile setegid seteuid \
sem_open sem_timedwait sem_clockwait sem_getvalue sem_unlink sendfile setegid seteuid \
setgid sethostname \
setlocale setregid setreuid setresuid setresgid setsid setpgid setpgrp setpriority setuid setvbuf \
sched_get_priority_max sched_setaffinity sched_setscheduler sched_setparam \
Expand Down
3 changes: 3 additions & 0 deletions pyconfig.h.in
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Expand Up @@ -887,6 +887,9 @@
/* Define to 1 if you have the `sched_setscheduler' function. */
#undef HAVE_SCHED_SETSCHEDULER

/* Define to 1 if you have the `sem_clockwait' function. */
#undef HAVE_SEM_CLOCKWAIT

/* Define to 1 if you have the `sem_getvalue' function. */
#undef HAVE_SEM_GETVALUE

Expand Down