bug#55628: debug-timer-check fails on macOS 11.6.6

["Mattias Engdegård" <mattiase@acm.org>]

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25 maj 2022 kl. 14.20 skrev Lars Ingebrigtsen <larsi@gnus.org>:
> 
> Mattias Engdegård <mattiase@acm.org> writes:
> 
>> Built with enable-checking, (debug-timer-check) returns nil.
>> It turns out that debug_timer_callback is never actually called, but I
>> haven't dug further than that.
>> 
>> This is on macOS 11.6.6 and HAVE_TIMERFD is not defined. Does this
>> code path work on other systems?
> 
> I tried this on Debian/bookworm (with nativecomp, but that probably
> doesn't make a difference), and I got nil there, too.

Thanks for checking. Apparently pending_signals is never set; handle_alarm_signal is never called.
More digging shows that set_alarm always sets the interval timer to at least 1 ms in the future even if the timer has expired.

The attached patch makes set_alarm signal SIGALRM immediately if the timer is due. We could call the signal handler directly but this way it should work correctly if the signal is masked at the moment. What do you think?


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diff --git a/src/atimer.c b/src/atimer.c
index 1c6c881fc0..c26904e1f0 100644
--- a/src/atimer.c
+++ b/src/atimer.c
@@ -297,11 +297,6 @@ set_alarm (void)
 {
   if (atimers)
     {
-#ifdef HAVE_SETITIMER
-      struct itimerval it;
-#endif
-      struct timespec now, interval;
-
 #ifdef HAVE_ITIMERSPEC
       if (0 <= timerfd || alarm_timer_ok)
 	{
@@ -337,20 +332,24 @@ set_alarm (void)
 	}
 #endif
 
-      /* Determine interval till the next timer is ripe.
-	 Don't set the interval to 0; this disables the timer.  */
-      now = current_timespec ();
-      interval = (timespec_cmp (atimers->expiration, now) <= 0
-		  ? make_timespec (0, 1000 * 1000)
-		  : timespec_sub (atimers->expiration, now));
+      /* Determine interval till the next timer is ripe.  */
+      struct timespec now = current_timespec ();
+      if (timespec_cmp (atimers->expiration, now) <= 0)
+	{
+	  /* Timer is (over)due -- just trigger the signal right way.  */
+	  raise (SIGALRM);
+	}
+      else
+	{
+	  struct timespec interval = timespec_sub (atimers->expiration, now);
 
 #ifdef HAVE_SETITIMER
-
-      memset (&it, 0, sizeof it);
-      it.it_value = make_timeval (interval);
-      setitimer (ITIMER_REAL, &it, 0);
-#endif /* not HAVE_SETITIMER */
-      alarm (max (interval.tv_sec, 1));
+	  struct itimerval it = {.it_value = make_timeval (interval)};
+	  setitimer (ITIMER_REAL, &it, 0);
+#else
+	  alarm (max (interval.tv_sec, 1));
+#endif
+	}
     }
 }