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Date:      Mon, 15 Oct 2012 15:21:31 -0700
From:      Xin Li <delphij@delphij.net>
To:        Garrett Cooper <yanegomi@gmail.com>
Cc:        Ian Lepore <freebsd@damnhippie.dyndns.org>, src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org>, Maxim Sobolev <sobomax@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   Re: svn commit: r241576 - in head/usr.sbin/cron: cron crontab lib
Message-ID:  <507C8C6B.80707@delphij.net>
In-Reply-To: <CAGH67wSATkcsMMFcd3=rkM%2BDZ=g-ke67zeuXd9RZ-=UY_9sdLg@mail.gmail.com>
References:  <201210150821.q9F8Lobc047576@svn.freebsd.org> <20121015202615.GJ1383@garage.freebsd.pl> <1350333885.1123.153.camel@revolution.hippie.lan> <CAGH67wSATkcsMMFcd3=rkM%2BDZ=g-ke67zeuXd9RZ-=UY_9sdLg@mail.gmail.com>

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On 10/15/12 13:52, Garrett Cooper wrote:
> On Mon, Oct 15, 2012 at 1:44 PM, Ian Lepore 
> <freebsd@damnhippie.dyndns.org> wrote:
>> On Mon, 2012-10-15 at 22:26 +0200, Pawel Jakub Dawidek wrote:
>>> On Mon, Oct 15, 2012 at 08:21:50AM +0000, Maxim Sobolev wrote:
>>>> Author: sobomax Date: Mon Oct 15 08:21:49 2012 New Revision:
>>>> 241576 URL: http://svn.freebsd.org/changeset/base/241576
>>>> 
>>>> Log: Add per-second scheduling into the cron(8). Right now
>>>> it's only available via the new @every_second shortcut.
>>>> ENOTIME to implement crontab(5) format extensions to allow
>>>> more flexible scheduling.
>>>> 
>>>> In order to address some concerns expressed by Terry Lambert 
>>>> while discussing the topic few years ago, about per-second
>>>> cron possibly causing some bad effects on /etc/crontab by
>>>> stat()ing it every second instead of every minute now (i.e.
>>>> atime update), only check that database needs to be reloaded
>>>> on every 60-th loop run. This should be close enough to the
>>>> current behaviour.
>>>> 
>>>> Add "@every_minute" shortcut while I am here.
>>> 
>>> Do I read the code correctly and the cron deamon will wake up
>>> every second now even if @every_second is not used at all?
>> 
>> It appears to, which I don't think is a bad thing at all.  But
>> the way it waits is to wake up, do some work, and go back to
>> sleep for an integer 1 second.  That will occasionally lead to a
>> second in which no wakeup happens, as the "do some work" part
>> always takes some fraction of a second.
> 
> This is silly. It should be waking up at the lowest common 
> denominator of time quanta, not every second; this could be
> determined via the crontab its managing.

This will break crontab change detection -- instead of pickup the
change in a minute, now you end up with the smallest common divisor.

BTW it seems that I need to clean dust on my forever WIP cron update
sooner :-/

Cheers,
- -- 
Xin LI <delphij@delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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