What is a plugin?

A plugin is any class which implements the IPlugin interface in org.jtrix.project.beatrix.plugins. At this stage we don't need to worry about what's in this interface, although it's quite simple.

Plugins are collected together into a plugin manager object. Any object which implements IPluginManager (in the same package as IPlugin) is considered a plugin manager.

Any class which thinks it might benefit from having a plugin-style architecture can be a plugin manager, and any class which wants to provide ``pluggable'' features can be a plugin. Here are some examples:

• The class WorkerPool is a tool that organises groups of worker netlets. But there are some application-specific things it doesn't know: what kind of resources they need, if any extra action is needed when a new one starts, etc. So WorkerPool is a plugin manager. It relies on plugins to provide this extra intelligence.
• The class ServiceManager is a tool that handles service requests from consumers, checking security, etc. But it doesn't carry the functionality of the services themselves. Therefore it is a plugin manager, relying on plugins themselves to provide the service functionality.
• The class Manager represents a manager netlet. It knows it should provide workers and services, but they could be of various kinds. Therefore it is a plugin manager. It relies on worker pools and service managers as plugins for those extra details. So we can see that WorkerPool and ServiceManager are plugins themselves as well as plugin managers.