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

1 files changed, 62 insertions, 19 deletions

diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index 09e53a1..25f58d9 100644
--- a/Python/thread_pthread.h
+++ b/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(