On 06/09/07 21:40, Petri Hintukainen wrote:
> On Sat, 2007-06-09 at 12:28 +0200, Udo Richter wrote:
>> And, from the original post:
>>> May 31 20:23:38 localhost vdr: [3413] System Time = Thu May 31 20:23:38 2007 (1180632218)
>>> May 31 20:23:38 localhost vdr: [3413] Local Time = Thu May 31 20:19:37 2007 (1180631977)
>>> May 31 20:21:01 localhost vdr: [3405] PANIC: watchdog timer expired - exiting!
>
> Turning clock is always very bad and dangerous thing to do. It can cause
> lot of other problems too, just to mention incomplete builds, duplicate
> cron jobs, destroyed logs and files, incomplete backups ...
>
>> The clock was set to 20:19:37, and the watchdog fires at 20:21:01 - 84
>> seconds later. There must be something different causing the watchdog to
>> expire.
>
> It might be even some plugin. All timeouts (cTimeMs, cCondVar,
> cCondWait) use current wall clock time to set the timeout.
> Example:
> cCondWait c;
> c.Wait(100);
>
> If clock is turned 2 minutes back in middle of this, the code will wait
> 120100 ms instead of 100ms ... Might cause some quite weird problems.
> I belive there's no way to change pthread_..._timedwait functions, but
> cTimeMs can be changed to use monotonic timers instead of gettimeofday
> (patch attached).
> ...
I have (finally, sorry for the big delay) adopted this patch (in the
attached form) to fix a problem with SVDRP connections when the system
time is adjusted.
While testing this, I found that on my system the monotonic clock
only has a resolution of 4000250 ns (about 4 ms), which in your original
patch would have caused VDR not to use the monotonic clock.
Are there actually systems that have a 1 ms resolution?
Or is there some parameter that needs to be adjusted to get a better
resolution?
Maybe we should set the limit to, say, 10 ms, so that systems like
mine can also benefit from this. After all, the advantage of having
a monotonous clock outweighs the courser resolution (typically such
timeouts are not below 10 ms).
Klaus
--- Makefile 2007/11/04 10:15:59 1.110
+++ Makefile 2007/12/02 11:29:22
@@ -20,7 +20,7 @@
MANDIR = $(PREFIX)/share/man
BINDIR = $(PREFIX)/bin
LOCDIR = ./locale
-LIBS = -ljpeg -lpthread -ldl -lcap -lfreetype -lfontconfig
+LIBS = -ljpeg -lpthread -ldl -lcap -lrt -lfreetype -lfontconfig
INCLUDES = -I/usr/include/freetype2
PLUGINDIR= ./PLUGINS
--- tools.c 2007/11/03 15:34:07 1.137
+++ tools.c 2007/12/02 11:52:31
@@ -545,6 +545,40 @@
uint64_t cTimeMs::Now(void)
{
+#if _POSIX_TIMERS > 0 && defined(_POSIX_MONOTONIC_CLOCK)
+ static bool initialized = false;
+ static bool monotonic = false;
+ struct timespec tp;
+ if (!initialized) {
+ // check if monotonic timer is available and provides enough accurate resolution:
+ if (clock_getres(CLOCK_MONOTONIC, &tp) == 0) {
+ long Resolution = tp.tv_nsec;
+ // require at least 10 ms resolution:
+ if (tp.tv_sec == 0 && tp.tv_nsec <= 10000000) {
+ if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0) {
+ dsyslog("cTimeMs: using monotonic clock (resolution is %ld ns)", Resolution);
+ monotonic = true;
+ }
+ else
+ esyslog("cTimeMs: clock_gettime(CLOCL_MONOTONIC) failed");
+ }
+ else
+ dsyslog("cTimeMs: not using monotonic clock - resolution is too bad (%ld s %ld ns)", tp.tv_sec, tp.tv_nsec);
+ }
+ else
+ esyslog("cTimeMs: clock_getres(CLOCK_MONOTONIC) failed");
+ initialized = true;
+ }
+ if (monotonic) {
+ if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+ return (uint64_t(tp.tv_sec)) * 1000 + tp.tv_nsec / 1000000;
+ esyslog("cTimeMs: clock_gettime(CLOCK_MONOTONIC) failed");
+ monotonic = false;
+ // fall back to gettimeofday()
+ }
+#else
+# warning Posix monotonic clock not available
+#endif
struct timeval t;
if (gettimeofday(&t, NULL) == 0)
return (uint64_t(t.tv_sec)) * 1000 + t.tv_usec / 1000;
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