Event Notification

Select/Poll provide single interface to both declare interest and retrieve events.
One system call for both operations.
Interest is not retained.
Old and stupid.  Sorry.

Available on almost every operating system.
Mac OS X does not support poll.  Why?

Does not scale with many file descriptors.
Application and kernel needs to check every possible file descriptor for readiness.
Imagine 100,000 file descriptors with just one ready event.
Poll is a little bit better.