The latest disappointment is that the Pi can't do real interrupts.
The poll() system call waits for an event on a file descriptor. Your program stops running and the kernel takes over, allowing other "stuff" to run until the kernel itself sees the event, then it un-stalls your program and lets it run.
in this thread:-
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=33&t=10377
As I said, I don't call that real interrupts but apparently Linux people do. :~