bpo-12822: use monotonic clock for condvar if possible (GH-11723)

Author: methane

Makefile.pre.in

@@ -939,7 +939,8 @@ regen-opcode-targets:
 		$(srcdir)/Python/opcode_targets.h.new
 	$(UPDATE_FILE) $(srcdir)/Python/opcode_targets.h $(srcdir)/Python/opcode_targets.h.new
 
-Python/ceval.o: $(srcdir)/Python/opcode_targets.h $(srcdir)/Python/ceval_gil.h
+Python/ceval.o: $(srcdir)/Python/opcode_targets.h $(srcdir)/Python/ceval_gil.h \
+		$(srcdir)/Python/condvar.h
 
 Python/frozen.o: $(srcdir)/Python/importlib.h $(srcdir)/Python/importlib_external.h \
 		$(srcdir)/Python/importlib_zipimport.h
@@ -1838,7 +1839,7 @@ patchcheck: @DEF_MAKE_RULE@
 
 # Dependencies
 
-Python/thread.o: @THREADHEADERS@
+Python/thread.o: @THREADHEADERS@ $(srcdir)/Python/condvar.h
 
 # Declare targets that aren't real files
 .PHONY: all build_all sharedmods check-clean-src oldsharedmods test quicktest

Misc/NEWS.d/next/Core and Builtins/2019-02-05-12-48-23.bpo-12822.0x2NDx.rst

@@ -0,0 +1,2 @@
+Use monotonic clock for ``pthread_cond_timedwait`` when
+``pthread_condattr_setclock`` and ``CLOCK_MONOTONIC`` are available.

Python/ceval.c

@@ -171,6 +171,7 @@ PyEval_InitThreads(void)
 {
     if (gil_created())
         return;
+    PyThread_init_thread();
     create_gil();
     take_gil(_PyThreadState_GET());
     _PyRuntime.ceval.pending.main_thread = PyThread_get_thread_ident();

Python/condvar.h

@@ -48,27 +48,17 @@
  * POSIX support
  */
 
-#define PyCOND_ADD_MICROSECONDS(tv, interval) \
-do { /* TODO: add overflow and truncation checks */ \
-    tv.tv_usec += (long) interval; \
-    tv.tv_sec += tv.tv_usec / 1000000; \
-    tv.tv_usec %= 1000000; \
-} while (0)
-
-/* We assume all modern POSIX systems have gettimeofday() */
-#ifdef GETTIMEOFDAY_NO_TZ
-#define PyCOND_GETTIMEOFDAY(ptv) gettimeofday(ptv)
-#else
-#define PyCOND_GETTIMEOFDAY(ptv) gettimeofday(ptv, (struct timezone *)NULL)
-#endif
+/* These private functions are implemented in Python/thread_pthread.h */
+int _PyThread_cond_init(PyCOND_T *cond);
+void _PyThread_cond_after(long long us, struct timespec *abs);
 
 /* The following functions return 0 on success, nonzero on error */
 #define PyMUTEX_INIT(mut)       pthread_mutex_init((mut), NULL)
 #define PyMUTEX_FINI(mut)       pthread_mutex_destroy(mut)
 #define PyMUTEX_LOCK(mut)       pthread_mutex_lock(mut)
 #define PyMUTEX_UNLOCK(mut)     pthread_mutex_unlock(mut)
 
-#define PyCOND_INIT(cond)       pthread_cond_init((cond), NULL)
+#define PyCOND_INIT(cond)       _PyThread_cond_init(cond)
 #define PyCOND_FINI(cond)       pthread_cond_destroy(cond)
 #define PyCOND_SIGNAL(cond)     pthread_cond_signal(cond)
 #define PyCOND_BROADCAST(cond)  pthread_cond_broadcast(cond)
@@ -78,22 +68,16 @@ do { /* TODO: add overflow and truncation checks */ \
 Py_LOCAL_INLINE(int)
 PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, long long us)
 {
-    int r;
-    struct timespec ts;
-    struct timeval deadline;
-
-    PyCOND_GETTIMEOFDAY(&deadline);
-    PyCOND_ADD_MICROSECONDS(deadline, us);
-    ts.tv_sec = deadline.tv_sec;
-    ts.tv_nsec = deadline.tv_usec * 1000;
-
-    r = pthread_cond_timedwait((cond), (mut), &ts);
-    if (r == ETIMEDOUT)
+    struct timespec abs;
+    _PyThread_cond_after(us, &abs);
+    int ret = pthread_cond_timedwait(cond, mut, &abs);
+    if (ret == ETIMEDOUT) {
         return 1;
-    else if (r)
+    }
+    if (ret) {
         return -1;
-    else
-        return 0;
+    }
+    return 0;
 }
 
 #elif defined(NT_THREADS)

Python/thread_pthread.h

@@ -56,16 +56,6 @@
 #endif
 #endif
 
-#if !defined(pthread_attr_default)
-#  define pthread_attr_default ((pthread_attr_t *)NULL)
-#endif
-#if !defined(pthread_mutexattr_default)
-#  define pthread_mutexattr_default ((pthread_mutexattr_t *)NULL)
-#endif
-#if !defined(pthread_condattr_default)
-#  define pthread_condattr_default ((pthread_condattr_t *)NULL)
-#endif
-
 
 /* Whether or not to use semaphores directly rather than emulating them with
  * mutexes and condition variables:
@@ -110,6 +100,56 @@ do { \
 } while(0)
 
 
+/*
+ * 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;
+
+static void
+init_condattr()
+{
+#ifdef CONDATTR_MONOTONIC
+    static pthread_condattr_t ca;
+    pthread_condattr_init(&ca);
+    if (pthread_condattr_setclock(&ca, CLOCK_MONOTONIC) == 0) {
+        condattr_monotonic = &ca;  // Use monotonic clock
+    }
+#endif
+}
+
+int
+_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;
+        return;
+    }
+#endif
+
+    struct timespec ts;
+    MICROSECONDS_TO_TIMESPEC(us, ts);
+    *abs = ts;
+}
+
+
 /* A pthread mutex isn't sufficient to model the Python lock type
  * because, according to Draft 5 of the docs (P1003.4a/D5), both of the
  * following are undefined:
@@ -146,6 +186,7 @@ PyThread__init_thread(void)
     extern void pthread_init(void);
     pthread_init();
 #endif
+    init_condattr();
 }
 
 /*
@@ -462,8 +503,7 @@ PyThread_allocate_lock(void)
         memset((void *)lock, '\0', sizeof(pthread_lock));
         lock->locked = 0;
 
-        status = pthread_mutex_init(&lock->mut,
-                                    pthread_mutexattr_default);
+        status = pthread_mutex_init(&lock->mut, NULL);
         CHECK_STATUS_PTHREAD("pthread_mutex_init");
         /* Mark the pthread mutex underlying a Python mutex as
            pure happens-before.  We can't simply mark the
@@ -472,8 +512,7 @@ PyThread_allocate_lock(void)
            will cause errors. */
         _Py_ANNOTATE_PURE_HAPPENS_BEFORE_MUTEX(&lock->mut);
 
-        status = pthread_cond_init(&lock->lock_released,
-                                   pthread_condattr_default);
+        status = _PyThread_cond_init(&lock->lock_released);
         CHECK_STATUS_PTHREAD("pthread_cond_init");
 
         if (error) {
@@ -532,9 +571,10 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
             success = PY_LOCK_ACQUIRED;
         }
         else if (microseconds != 0) {
-            struct timespec ts;
-            if (microseconds > 0)
-                MICROSECONDS_TO_TIMESPEC(microseconds, ts);
+            struct timespec abs;
+            if (microseconds > 0) {
+                _PyThread_cond_after(microseconds, &abs);
+            }
             /* continue trying until we get the lock */
 
             /* mut must be locked by me -- part of the condition
@@ -543,10 +583,13 @@ PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
                 if (microseconds > 0) {
                     status = pthread_cond_timedwait(
                         &thelock->lock_released,
-                        &thelock->mut, &ts);
+                        &thelock->mut, &abs);
+                    if (status == 1) {
+                        break;
+                    }
                     if (status == ETIMEDOUT)
                         break;
-                    CHECK_STATUS_PTHREAD("pthread_cond_timed_wait");
+                    CHECK_STATUS_PTHREAD("pthread_cond_timedwait");
                 }
                 else {
                     status = pthread_cond_wait(

configure

@@ -11448,7 +11448,8 @@ for ac_func in alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  memrchr mbrtowc mkdirat mkfifo \
  mkfifoat mknod mknodat mktime mremap nice openat pathconf pause pipe2 plock poll \
  posix_fallocate posix_fadvise posix_spawn posix_spawnp pread preadv preadv2 \
- pthread_init pthread_kill putenv pwrite pwritev pwritev2 readlink readlinkat readv realpath renameat \
+ pthread_condattr_setclock pthread_init pthread_kill putenv pwrite pwritev pwritev2 \
+ readlink readlinkat readv realpath renameat \
  sem_open sem_timedwait sem_getvalue sem_unlink sendfile setegid seteuid \
  setgid sethostname \
  setlocale setregid setreuid setresuid setresgid setsid setpgid setpgrp setpriority setuid setvbuf \

configure.ac

@@ -3506,7 +3506,8 @@ AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  memrchr mbrtowc mkdirat mkfifo \
  mkfifoat mknod mknodat mktime mremap nice openat pathconf pause pipe2 plock poll \
  posix_fallocate posix_fadvise posix_spawn posix_spawnp pread preadv preadv2 \
- pthread_init pthread_kill putenv pwrite pwritev pwritev2 readlink readlinkat readv realpath renameat \
+ pthread_condattr_setclock pthread_init pthread_kill putenv pwrite pwritev pwritev2 \
+ readlink readlinkat readv realpath renameat \
  sem_open sem_timedwait sem_getvalue sem_unlink sendfile setegid seteuid \
  setgid sethostname \
  setlocale setregid setreuid setresuid setresgid setsid setpgid setpgrp setpriority setuid setvbuf \

pyconfig.h.in

@@ -765,6 +765,9 @@
 /* Define if your compiler supports function prototype */
 #undef HAVE_PROTOTYPES
 
+/* Define to 1 if you have the `pthread_condattr_setclock' function. */
+#undef HAVE_PTHREAD_CONDATTR_SETCLOCK
+
 /* Defined for Solaris 2.6 bug in pthread header. */
 #undef HAVE_PTHREAD_DESTRUCTOR