From: Eric Wong <normalperson@...>
Date: 2011-06-29T04:22:22+09:00
Subject: Re: clock-scheduled operations

Chad Perrin <code@apotheon.net> wrote:
> Obviously, scheduling something to happen every foo seconds is easy.
> What is a reasonably performant, simple way to schedule an operation to
> occur at a particular time of day (preferably specified by a particular
> time zone)?

If it has to be within a long-running program:

You can install a signal handler and have cron signal the process.

I don't know of anything that takes care of timezones/calculations for
you, but...

> The first thing that comes to my mind is checking Time.now, checking the
> time between that and the desired time of day, then spawn a thread that
> sleeps for that length of time (because I need the program to do other
> things in the meantime).  Is there a better way to do this?

Cool.io and EventMachine both expose timer functionality which should
be reasonably portable across different *nixes.

If you're only targetting recent-ish Linux systems, the
sleepy_penguin[1] library exposes TimerFD as an IO object which you can
IO.select/poll/epoll on.  This functionality is only lightly-tested,
so feedback is welcome (I'm the maintainer).

[1] http://bogomips.org/sleepy_penguin/

-- 
Eric Wong