Introduction to OS X Notification Overview
Notifications are a means of sharing state information between two applications, daemons, or other processes in a way that is robust while maintaining good performance.
You should read this document if you are writing an application that uses interprocess communication. You should also read this document if you need to learn about Darwin notifications (including kernel event notifications).
Organization of This Document
This document is organized into four chapters:
Notification Basics—describes notifications at a high level.
Choosing a Notification Technology—highlights the differences between notification technologies and provides guidance about what notification API you should use under different circumstances.
Darwin Notification Concepts—describes the Darwin notification mechanism.
Alternatives to Notification—describes alternatives to notifications and provides guidelines for their use.