/**
 @page engine_controller Engine Controller module

 @section Overview
Engine Controller module provides encapsulated multi-thread environment plus its control.<br>

 @image html overview_engine_controller.png "Software architecture of Engine Controller module"

It uses an internal object called "Task", and it contains
	- A pointer to a user-registered function
	- Input/output parameters of the function and relationship to other Tasks

Engine Controller provides two kinds of Tasks - Sync and Async.
	- Sync Tasks return after execution finish.
	- Async Tasks return before execution finish, and afterwards call user-specified callback when the execution finished.

User need to define and register expected Tasks in advnace before using it.<br>
And by registering queueing rule connected to user Tasks, user may control their processing order.<br>
For example, precedent condition such as "Task B should be executed after Task A has finished." can be specified.

Engine Controller module has following sub implementations with each corresponding roles.<br>
	- <b>Task generator</b><br>
	Provides APIs to generate and register Task object, and to register between-Tasks relationship called "Queuing rule".<br>

	- <b>Task Manager</b><br>
	Manages user-registered Tasks and their relationship with other Tasks internally.<br>

	- <b>Task Executor</b><br>
	Executes/cancels user-registerd Tasks on demand.<br>
*/