tickless cron

[Rogelio Serrano]

On 9/1/06, walter harms <wharms at bfs.de> wrote:
>
>
> Rogelio Serrano wrote:
> > On 9/1/06, walter harms <wharms at bfs.de> wrote:
> >> hi,
> >> i am courious,
> >> setting an timeout will be risky if a task in between takes more time
> >> than anticipated
> >> causing an overrun. (think or a datatransfer every 1minute that takes
> >> 1.5 minutes).
> >> why should i do it ?
> >>
> >
> > you dont understand my question.
> >
> >> i do not think that you will win much but that. on the other hand if
> >> you need it to start
> >> at sunday,11:00 you can use at. what is much better suited for that.
> >>
> >> inotify is nice but has changed a lot and is a challenge to support it
> >> between
> >> different kernel versions. and frankly stat() is not a bad solution.
> >>
> >> re,
> >>  wh
> >
> > tickless kernel does this already.
> >
> > the timers are in a sorted list. everytime a new timer is inserted the
> > list is sorted and the timer with the closest timeout is chosen.
> >
> > my main problem is computing the next timeout given a crontab format
> > schedule string.
> >
> > for example: given "60 * * * * *" when is the next timeout from now?
> >
> that means "every 60 minutes" or when the minute counter == 60 and rest is anything.
> (of cause 60m will not work but it does not matter here)
>
> > or "12 60 * * * *" when is the next timeout?
> >
> same here read as (minute counter == 12) && (hour counter == 60) && (rest == anything)
>
> complicated are stuff like "next 3. Friday this month". i guess you need to recalculate
> everytime you encounter it.
>
> so your basic idea is to calculate the next epoch the command should be executed, and then
> recalculated the next epoch every time.
>
> did i get the point now ?
>
> re,
>  wh
>

yes thats right. so these epochs are placed in a priority queue. then
a timer, like select, is programmed by the difference between the
current time and next epoch.

-- 
things i hate about my linux pc:

1. it takes more than a second to boot up
2. keeps asking about filenames and directories
3. does not remember what i was working on yesterday
4. does not remember all the changes i have ever made
5.cannot figure out necessary settings by itself