Description of problem:
The at daemon sleeps for 3600 seconds at a time if there is no task to run in the next hour. If during this, the computer is suspended to RAM, when it resumes, the kernel will continue the nanosleep, sleeping for the remaining (up to 3600) seconds.

The problem is, if there is a task scheduled in the minutes after the resume, they will usually be run late. In my case I use 'at' to schedule my alarm clock, then use the rtc alarm function of my BIOS to wake the computer a couple of minutes before my alarm goes off. If atd sleeps for almost an hour past this desired time, it's not a very effective method.

Is there some way to patch atd so that it gets some kind of signal on a resume from suspend (I imagine the problem also occurs with hibernate). Alternatively, is there a sleep call that attempts to sleep in wall time (if such a system call exists) -- that is, sleep until this many seconds past Jan 01 1970, as oppose to sleep for x seconds; this would mean the sleep would finish just after resume, as the wall time would be well and truly past what it should be?

As a current workaround, I have put the following script in /etc/pm/sleep.d/signal_atd:
#!/bin/sh
# When resuming, send atd a SIGHUP to recalculate sleep timer

if [ "$1" == "resume" -a -f /var/run/atd.pid ]; then
	pid=`cat /var/run/atd.pid`
	if [ -d "/proc/$pid" ]; then
		kill -HUP "$pid"
	fi
fi

Version-Release number of selected component (if applicable):
at-3.1.10-23.fc9.i386

How reproducible:
Very.

Steps to Reproduce:
1. Schedule a job using 'at' for the current time plus 65 minutes
2. Suspend the system for 10 minutes (or more), then resume
3. Check what time the job runs.
  
Actual results:
The job is run at least 5 minutes later than it should have. If you suspended the system for 60 minutes at step 2, it would have run the job almost 60 minutes late.


Expected results:
If the system is running, run the requested jobs at the right time. So, given that the system is no longer in suspend, it should be able to service requests as usual.


Additional info:
An strace -t -T gives something like:
04:09:47 nanosleep({3600, 0}, 0xbf84c4e4) = ? ERESTART_RESTARTBLOCK (To be restarted) <31763.781788>
12:59:11 restart_syscall(<... resuming interrupted call ...>) <3496.452345>