bpo-32243: Use monotonic clock for thread timeouts; more flexibility for very small switch intervals

Makefile.pre.in

@@ -939,7 +939,7 @@ 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 +1838,7 @@ 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

Python/condvar.h

@@ -48,44 +48,69 @@
  * 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
+#include <pthread.h>
 
 /* 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_T pthread_cond_t
 #define PyCOND_FINI(cond)       pthread_cond_destroy(cond)
 #define PyCOND_SIGNAL(cond)     pthread_cond_signal(cond)
 #define PyCOND_BROADCAST(cond)  pthread_cond_broadcast(cond)
 #define PyCOND_WAIT(cond, mut)  pthread_cond_wait((cond), (mut))
 
+#if HAVE_PTHREAD_CONDATTR_SETCLOCK
+#define MONOTONIC
+#else
+#undef MONOTONIC
+#endif
+
+Py_LOCAL_INLINE(int)
+PyCOND_INIT(PyCOND_T *cond)
+{
+    pthread_condattr_t attr;
+    int err;
+
+    (void)pthread_condattr_init(&attr);
+#ifdef MONOTONIC
+    err = pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
+    if (err)
+        return err;
+#endif
+    err = pthread_cond_init(cond, &attr);
+    (void)pthread_condattr_destroy(&attr);
+    return err;
+}
+
+# ifdef MONOTONIC
+# define GETTIME _PyTime_GetMonotonicClock
+# else
+# define GETTIME _PyTime_GetSystemClock
+# endif
+
+# define MAXIMUM_TIMEOUT 100
+
 /* return 0 for success, 1 on timeout, -1 on error */
 Py_LOCAL_INLINE(int)
-PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, long long us)
+PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, PY_TIMEOUT_T 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;
+    _PyTime_t deadline;
+
+    while (1) {
+        _PyTime_t delta;
+        deadline = GETTIME() + _PyTime_FromNanoseconds(us * 1000);
+        if (us < MAXIMUM_TIMEOUT && ((delta=(GETTIME() - deadline)) > 0)) {
+            us += _PyTime_AsMicroseconds(delta, _PyTime_ROUND_CEILING);
+            continue;
+        }
+        _PyTime_AsTimespec(deadline, &ts);
+        break;
+    }
 
     r = pthread_cond_timedwait((cond), (mut), &ts);
     if (r == ETIMEDOUT)

Python/thread_pthread.h

@@ -75,6 +75,11 @@
 #  define USE_SEMAPHORES
 #else
 #  undef USE_SEMAPHORES
+#  if HAVE_PTHREAD_CONDATTR_SETCLOCK
+#    define MONOTONIC
+#  else
+#    undef MONOTONIC
+#  endif
 #endif
 
 
@@ -89,24 +94,16 @@
 #  define SET_THREAD_SIGMASK sigprocmask
 #endif
 
-
-/* We assume all modern POSIX systems have gettimeofday() */
-#ifdef GETTIMEOFDAY_NO_TZ
-#define GETTIMEOFDAY(ptv) gettimeofday(ptv)
+#ifdef MONOTONIC
+#define GETTIME _PyTime_GetMonotonicClock
 #else
-#define GETTIMEOFDAY(ptv) gettimeofday(ptv, (struct timezone *)NULL)
+#define GETTIME _PyTime_GetSystemClock
 #endif
 
-#define MICROSECONDS_TO_TIMESPEC(microseconds, ts) \
+#define MICROSECONDS_TO_TIMESPEC(us, ts) \
 do { \
-    struct timeval tv; \
-    GETTIMEOFDAY(&tv); \
-    tv.tv_usec += microseconds % 1000000; \
-    tv.tv_sec += microseconds / 1000000; \
-    tv.tv_sec += tv.tv_usec / 1000000; \
-    tv.tv_usec %= 1000000; \
-    ts.tv_sec = tv.tv_sec; \
-    ts.tv_nsec = tv.tv_usec * 1000; \
+    _PyTime_t t = GETTIME() + _PyTime_FromNanoseconds(us * 1000); \
+    _PyTime_AsTimespec(t, &ts); \
 } while(0)
 
 
@@ -452,6 +449,7 @@ PyThread_allocate_lock(void)
 {
     pthread_lock *lock;
     int status, error = 0;
+    pthread_condattr_t attr;
 
     dprintf(("PyThread_allocate_lock called\n"));
     if (!initialized)
@@ -472,9 +470,14 @@ 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);
+        pthread_condattr_init(&attr);
+#ifdef MONOTONIC
+        status = pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
+        CHECK_STATUS_PTHREAD("pthread_condattr_setclock");
+#endif
+        status = pthread_cond_init(&lock->lock_released, &attr);
         CHECK_STATUS_PTHREAD("pthread_cond_init");
+        pthread_condattr_destroy(&attr);
 
         if (error) {
             PyMem_RawFree((void *)lock);

configure

@@ -10878,12 +10878,13 @@ $as_echo "#define HAVE_BROKEN_PTHREAD_SIGMASK 1" >>confdefs.h
 fi
 done
 
-      for ac_func in pthread_getcpuclockid
+      for ac_func in pthread_getcpuclockid pthread_condattr_setclock
 do :
-  ac_fn_c_check_func "$LINENO" "pthread_getcpuclockid" "ac_cv_func_pthread_getcpuclockid"
-if test "x$ac_cv_func_pthread_getcpuclockid" = xyes; then :
+  as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
+ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
+if eval test \"x\$"$as_ac_var"\" = x"yes"; then :
   cat >>confdefs.h <<_ACEOF
-#define HAVE_PTHREAD_GETCPUCLOCKID 1
+#define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
 _ACEOF
 
 fi

configure.ac

@@ -3157,7 +3157,7 @@ if test "$posix_threads" = "yes"; then
             [Define if pthread_sigmask() does not work on your system.])
             ;;
         esac])
-      AC_CHECK_FUNCS(pthread_getcpuclockid)
+      AC_CHECK_FUNCS([pthread_getcpuclockid pthread_condattr_setclock])
 fi