linux-kernel - Re: Real time clock update notification

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Message-ID: <1327760814.5816.1.camel@lenny>
Date:	Sat, 28 Jan 2012 09:26:54 -0500
From:	Colin Walters <walters@...bum.org>
To:	Bob Richmond <bob@...ez.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Real time clock update notification

On Fri, 2012-01-27 at 14:52 -0800, Bob Richmond wrote:
> Is there any kind of facility for a process that is blocking in any one 
> of the event notification system calls (select/poll/epoll_wait) to be 
> unblocked in the event that the realtime clock has been updated? For 
> instance, say I want to fire off an event at the exact moment that the 
> realtime clock flips to 2pm. I first query the realtime clock via 
> clock_gettime(CLOCK_REALTIME), and know that in 3 hours, it will be 2pm 
> and I want to unblock at that moment. So I block in epoll_wait for 3 hours.

You're looking for "timerfd".  Our use in GNOME is here:

http://git.gnome.org/browse/gnome-desktop/tree/libgnome-desktop/gnome-datetime-source.c

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