Why Apache Commons Exec Needs the Watchdog Working as Observer?

Currently, I can’t see the requirements.

Watchdog & Observer Design Pattern

What is Observer Pattern

http://en.wikipedia.org/wiki/Observer_pattern

The observer pattern (a subset of the publish/subscribe pattern) is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is mainly used to implement distributed event handling systems.