> I never found the source of the problem, but it hasn't happened again since
> that one time. Does just plain sleep(1) sleep forever (in nanosleep?)

That's exactly it.  I have a simple program which is basically a loop of
	open, read, close a file
	broadcast a packet on the local ethernet with send()
	sleep(1);

and it is now hanging in nanosleep after running for just a few minutes.
What is strange is that this had been working perfectly for a year, but
suddenly started going haywire about a week ago (and repeatably so), after
I rebooted my system due to mysteriously runniing out of swap space.