[Spread-users] Should I dare touch the clock?
drago.krznaric at se.transport.bombardier.com
drago.krznaric at se.transport.bombardier.com
Mon May 11 04:18:18 EDT 2009
Thanky you for prompt reply. If I would like to try to use the monotonic
clock, do you know if there
is some test suite I could use to see that things work after the change?
Please consider the environment before you print / Merci de penser à
l'environnement avant d'imprimer / Tänk på miljön innan du skriver ut
John Schultz <jschultz at spreadconcepts.com>
2009-05-08 17:50
To
Drago Krznaric/SE/Transport/Bombardier at TRANSPORT
cc
spread-users at lists.spread.org
Subject
Re: [Spread-users] Should I dare touch the clock?
Spread currently uses the wall clock time for all of its time based
calculations. If you only move the clock a little, then you probably
won't have any issues, although I'm not 100% sure. If you drastically
jump the clock forward, then I can see major issues as suddenly the
already scheduled timeouts will take forever to fire. If you drastically
jump the clock backwards, then a lot of timeouts will fire prematurely,
which might cause a spurious partition or something, but the system would
probably then return to normal operations immediately thereafter.
The events system definitely should be moved over to using a monotonic
clock on whatever platforms such a service is available. We would like to
do this sometime in the future, but if you experiment with it and get
something to work and want to contribute it back, then that would be
great.
Cheers!
John
---
John Lane Schultz
Spread Concepts LLC
Phn: 443 838 2200
Fax: 301 560 8875
Friday, May 8, 2009, 11:19:23 AM, you wrote:
>
Hi,
I have a single spread daemon and a bunch of programs communicating via
spread messages
through this daemon. All programs and the daemon are running on the same
machine.
>From previous mails on this list, I know that people have had problems
with message
delivery when they have changed the clock, via settimeofday and even NTP.
But I'm not sure if this can only occur when there are multiple daemons or
if it can happen
in my case too. Browsing through the code in events.c, it looks as it
could happen in my case
too, although the probability is perhaps small.
Has someone a testprogram/argument proving that this is either true or
false?
I'm thinking about changing the gettimeofday call in E_get_time to
something that is not
affected by some external source setting the time, for example,
clock_gettime(CLOCK_MONOTONIC).
Has someone done something similar before?
Cheers,
Drago
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