[erlang-bugs] R15B01 erlang:now() jumping ~24 days into the future

Garret Smith <>
Tue Mar 12 16:36:37 CET 2013


On Mar 12, 2013 6:38 AM, "Patrik Nyblom" <> wrote:
>
> Hi!
>
> There's a patched version of the R15B02 dll in my public dropbox, under
the name r15.beam.smp.dll:
>
> http://dl.dropbox.com/u/17212223/r15.beam.smp.dll

R15B02 will work.  I'll get started but it will take a couple days to get
everything built, deployed and watch for time jumps.

Thank you for the binary!

>
> If you replace the R15 beam.smp.dll with this one, the werl slogan should
contain the version erts-5.9.2.0.1, if you could try that on the real app,
I would be immensely grateful!
>
> Cheers,
> /Patrik
>
> On 03/12/2013 02:09 PM, Vance Shipley wrote:
>>
>> C
>>
>> On Mar 5, 2013 6:56 AM, "Garret Smith" <> wrote:
>>>
>>> I have been beating my head against a wall for weeks tracking down
spooky behaviour[sic] in one of our production systems.  I finally tracked
it down to "jumps" in the times returned by erlang:now(), causing all
timers in the system to expire at once.  I have witnessed this bug on
R15B01, both 64 and 32-bit versions running on Windows Server 2008 R2, both
on bare metal and VirtualBox VM.
>>>
>>> The time jump is always around 2126000 seconds, or a little over 24
days.  The now() time does not try to converge with os:timestamp() as the
documentation suggests, and as I confirmed it does if you just change the
system clock.
>>>
>>> Another VM running concurrently on the same machine but with little
load (diagnostic node & production node) did not time jump.
>>>
>>> Higher load seems to make the time jumps happen more often.
>>>
>>> Frequency between time jumps varies between seconds and hours, but when
a jump occurs, it is always 2126000 + (9 to 26) seconds.
>>>
>>> I never see the jump in logfile timestamps that use os:timestamp() for
tagging log messages.  I had to start tracing a production node before I
caught the jump.  Here are some lines from a trace, where the timestamp in
trace_ts is printed using calendar:now_to_local_time() and then in raw
tuple format:
>>>
>>> 2013-4-16 21:40:1.993399|{1366,173601,993399}
>>> 2013-4-16 21:40:1.993400|{1366,173601,993400}
>>> 2013-5-11 12:13:41.986961|{1368,299621,986961}
>>> 2013-5-11 12:13:41.986962|{1368,299621,986962}
>>>
>>> then a bit later...
>>>
>>> 2013-5-11 12:36:19.955129|{1368,300979,955129}
>>> 2013-5-11 12:36:19.955130|{1368,300979,955130}
>>> 2013-6-5 3:9:49.538830|{1370,426989,538830}
>>> 2013-6-5 3:9:49.538833|{1370,426989,538833}
>>>
>>> I captured many such jumps over the course of a day or so.  Obviously
from the dates, 2 jumps happened before I started tracing.
>>>
>>> I was able to reproduce the bug, though not as efficiently as my
production system, with the following sample program:
https://gist.github.com/garret-smith/5087169
>>>
>>> It took over an hour of runtime before the first time jump.  I am
working on a better way to reproduce it at the moment, but it's hard to
test the test with a bug so intermittent.
>>>
>>> I am also testing various other VM versions.  My first hope was that
this was limited to the 64-bit version where we first encountered the
problem, but a change to the 32-bit version has only made the problem
happen less often, not eliminated it.
>>>
>>> We never saw this bug with R14B03 which we were running previously to
R15B01.  However, system load is different so I can't make a direct
comparison.  I did notice a few significant updates to the Windows time
related code between R14B03 and R15:
>>>
>>> git log sys_time.c
>>>
>>> commit 46eb4359b05b220861453a869dc734480ec045a6
>>> Author: Patrik Nyblom <>
>>> Date:   Tue Dec 6 19:07:16 2011 +0100
>>>
>>>     Emulate localtime, gmtime and mktime to enable negative time_t
>>>
>>> commit 913f05af100e98a8665bbb6168e89fbcfe4ece75
>>> Author: Bj<C3><B6>rn-Egil Dahlberg <>
>>> Date:   Fri Dec 2 15:25:06 2011 +0100
>>>
>>>     Teach windows sys_localtime_r
>>>
>>>
>>> I am completely stumped.  What can I do next to help track down the
source of the bug?
>>>
>>> Thanks,
>>> Garret Smith
>>>
>>> _______________________________________________
>>> erlang-bugs mailing list
>>> 
>>> http://erlang.org/mailman/listinfo/erlang-bugs
>>>
>>
>>
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