How to figure out what process is preventing sleep?

FROM : Peter Creath
DATE : Tue Jun 20 21:28:36 2006

Is there any way to ask the root power manager to log what events or
processes are tickling it?  I'd at least like to know when it's being
tickled and by what process.  It would also be useful to know what
kind of tickle it's receiving -- e.g. via UpdateSystemActivity() or
disk accesses, or even an IOCancelPowerChange() response to a
kIOMessageCanSystemSleep message.

I've scoured the documentation, and I don't see any clear way to trap
this kind of information.  Any clever ideas out there?