[Python-checkins] bpo-41710: PyThread_acquire_lock_timed() uses sem_clockwait() (GH-28671) (GH-28683)
vstinner
webhook-mailer at python.org
Fri Oct 1 12:51:28 EDT 2021
https://github.com/python/cpython/commit/0e1aeab5d7de3f328876aea8ccabbc6db146a883
commit: 0e1aeab5d7de3f328876aea8ccabbc6db146a883
branch: 3.9
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: vstinner <vstinner at python.org>
date: 2021-10-01T18:51:15+02:00
summary:
bpo-41710: PyThread_acquire_lock_timed() uses sem_clockwait() (GH-28671) (GH-28683)
On Unix, if the sem_clockwait() function is available in the C
library (glibc 2.30 and newer), the threading.Lock.acquire() method
now uses the monotonic clock (time.CLOCK_MONOTONIC) for the timeout,
rather than using the system clock (time.CLOCK_REALTIME), to not be
affected by system clock changes.
configure now checks if the sem_clockwait() function is available.
(cherry picked from commit 6df8c327532627d6a99991993c52e8e4a9b34968)
Co-authored-by: Victor Stinner <vstinner at python.org>
files:
A Misc/NEWS.d/next/Library/2021-09-30-23-00-18.bpo-41710.svuloZ.rst
M Python/thread_pthread.h
M configure
M configure.ac
M pyconfig.h.in
diff --git a/Misc/NEWS.d/next/Library/2021-09-30-23-00-18.bpo-41710.svuloZ.rst b/Misc/NEWS.d/next/Library/2021-09-30-23-00-18.bpo-41710.svuloZ.rst
new file mode 100644
index 0000000000000..d8a4f9507c189
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-09-30-23-00-18.bpo-41710.svuloZ.rst
@@ -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.
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index e6910b3083a89..83974b4c0ca3b 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -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
@@ -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;
@@ -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
@@ -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",
@@ -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) {
@@ -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));
@@ -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();
@@ -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)
diff --git a/configure b/configure
index ffa61c1dc5126..7cad0e2f98ba1 100755
--- a/configure
+++ b/configure
@@ -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 \
diff --git a/configure.ac b/configure.ac
index 8fe5fa5742e8b..be28e3a38f7ab 100644
--- a/configure.ac
+++ b/configure.ac
@@ -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 \
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 6358e568f4a6f..b62e169255d99 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -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
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