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

Patrik Nyblom <>
Thu Apr 4 16:43:31 CEST 2013


Hi!

On 03/12/2013 04:36 PM, Garret Smith wrote:
>
>
> On Mar 12, 2013 6:38 AM, "Patrik Nyblom" < 
> <mailto:>> 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!
>
Any progress? Does it work (just curious :))

Cheers,
/Patrik
>
> >
> > 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" < 
> <mailto:>> 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 < <mailto:>>
> >>> 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 < 
> <mailto:>>
> >>> 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
> >>>  <mailto:>
> >>> http://erlang.org/mailman/listinfo/erlang-bugs
> >>>
> >>
> >>
> >> _______________________________________________
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> >
> >
> >
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