Hi Samuel,
OK, maybe you are correct regarding the abstime parameter.
However, the man page for pthread_cond_init(3) says:
The abstime parameter specifies an absolute time, with the same origin
as time(2) and gettimeofday(2): an abstime of 0 corresponds to 00:00:00
GMT, January 1, 1970.
This is not consistent with CLOCK_MONOTONIC on GNU/Hurd.
Could this be causing a misalignment in java? I am getting hangs on
pthread_cond_timedwait().
Damien
On 18/8/26 10:07 am, Samuel Thibault wrote:
> Hello,
>
> Damien Zammit, le lun. 17 août 2026 23:49:24 +0000, a ecrit:
>> When clock_id is CLOCK_MONOTONIC, there is an assumption
>> that abstime parameter is actually a relative time
> Where is such assumption?
>
> pthread_cond_timedwait always take an absolute time.
>
>> but the code was not making that assumption and getting the timeout
>> wrong.
>>
>> This is not tested, but according to OpenJDK 1.7.0 sources:
>>
>> if ((status = pthread_condattr_setclock(_condattr, CLOCK_MONOTONIC)) !=
>> 0) {
>> if (status == EINVAL) {
>> warning("Unable to use monotonic clock with relative timed-waits" \
>> " - changes to the time-of-day clock may have adverse
>> affects");
>>
>> So there are sources out there making this assumption.
> I believe the "relative" word above is misunderstood. It doesn't mean
> that the value is relative to "time now", but that it is relative to
> e.g. the machine bootup, and not an absolute time which will be affected
> by time-of-day changes. That's exactly what selecting CLOCK_MONOTONIC
> means: get something that monitors actual time that passes, and not the
> wall-clock time.
>
> Even with CLOCK_MONOTONIC, pthread_cond_timedwait should be given values
> akin to what clock_gettime() returns.
>
> Samuel
>
>> ---
>> .../hurd-pt-timedblock-relative.diff | 54 +++++++++++++++++++
>> debian/patches/series | 1 +
>> 2 files changed, 55 insertions(+)
>> create mode 100644
>> debian/patches/hurd-i386/hurd-pt-timedblock-relative.diff
>>
>> diff --git a/debian/patches/hurd-i386/hurd-pt-timedblock-relative.diff
>> b/debian/patches/hurd-i386/hurd-pt-timedblock-relative.diff
>> new file mode 100644
>> index 00000000..a7819ce3
>> --- /dev/null
>> +++ b/debian/patches/hurd-i386/hurd-pt-timedblock-relative.diff
>> @@ -0,0 +1,54 @@
>> +--- a/sysdeps/mach/htl/pt-timedblock.c
>> ++++ b/sysdeps/mach/htl/pt-timedblock.c
>> +@@ -40,23 +40,37 @@
>> + mach_msg_timeout_t timeout;
>> + struct timespec now;
>> +
>> +- /* We have an absolute time and now we have to convert it to a
>> +- relative time. Arg. */
>> +
>> +- err = __clock_gettime (clock_id, &now);
>> +- assert (!err);
>> ++ if (clock_id == CLOCK_MONOTONIC)
>> ++ {
>> ++ /* abstime param should be a relative time */
>> ++ if (abstime->tv_sec < 0
>> ++ || (abstime->tv_sec == 0 && abstime->tv_nsec < 0))
>> ++ return ETIMEDOUT;
>> +
>> +- if (now.tv_sec > abstime->tv_sec
>> +- || (now.tv_sec == abstime->tv_sec && now.tv_nsec > abstime->tv_nsec))
>> +- return ETIMEDOUT;
>> +-
>> +- timeout = (abstime->tv_sec - now.tv_sec) * 1000;
>> +-
>> +- if (abstime->tv_nsec >= now.tv_nsec)
>> +- timeout += (abstime->tv_nsec - now.tv_nsec + 999999) / 1000000;
>> ++ timeout = abstime->tv_sec * 1000 + (abstime->tv_nsec + 999999) /
>> 1000000;
>> ++ }
>> + else
>> +- /* Need to do a carry. */
>> +- timeout -= (now.tv_nsec - abstime->tv_nsec + 999999) / 1000000;
>> ++ {
>> ++ /* We have an absolute time and now we have to convert it to a
>> ++ relative time. This codepath could be avoided by using
>> CLOCK_MONOTONIC
>> ++ and passing a relative time for the abstime parameter. */
>> ++
>> ++ err = __clock_gettime (clock_id, &now);
>> ++ assert (!err);
>> ++
>> ++ if (now.tv_sec > abstime->tv_sec
>> ++ || (now.tv_sec == abstime->tv_sec && now.tv_nsec >
>> abstime->tv_nsec))
>> ++ return ETIMEDOUT;
>> ++
>> ++ timeout = (abstime->tv_sec - now.tv_sec) * 1000;
>> ++
>> ++ if (abstime->tv_nsec >= now.tv_nsec)
>> ++ timeout += (abstime->tv_nsec - now.tv_nsec + 999999) / 1000000;
>> ++ else
>> ++ /* Need to do a carry. */
>> ++ timeout -= (now.tv_nsec - abstime->tv_nsec + 999999) / 1000000;
>> ++ }
>> +
>> + err = __mach_msg (&msg, MACH_RCV_MSG | MACH_RCV_TIMEOUT | MSG_OPTIONS, 0,
>> + sizeof msg, thread->wakeupmsg.msgh_remote_port,
>> diff --git a/debian/patches/series b/debian/patches/series
>> index f4346bf6..4d9ea389 100644
>> --- a/debian/patches/series
>> +++ b/debian/patches/series
>> @@ -41,6 +41,7 @@ hurd-i386/submitted-bind_umask2.diff
>> hurd-i386/tg-bootstrap.diff
>> hurd-i386/local-no_unsupported_ioctls.diff
>> hurd-i386/local-stack_chk_guard.diff
>> +hurd-i386/hurd-pt-timedblock-relative.diff
>>
>> i386/local-biarch.diff
>> i386/unsubmitted-quiet-ldconfig.diff
>> --
>> 2.51.0
>>
>>
>>
> --
> Samuel
> War doesn't prove who's right, just who's left.
