Explore Patterns in Context-Aware Applications

--Using Reactor Pattern to Develop In/Out Board

Fall 2002

Yu Du

Outline

Motivation Pattern definition In / Out Board using Reactor Pattern

– Requirements– Design– Reactor Pattern– Screen shots

Conclusions

Motivation

Context-aware applications is complex. Patterns are a recent software engineering

problem-solving discipline. An attempt to describe good designs, and

capture experience for reuse. “The long term goal is to develop handbooks

for software engineers.”

Explore patterns in context-aware applications development.

What is pattern

A pattern is a reusable solution to a recurring problem. Context Program structure Participants Consequences: both positive and negative Examples!

Pattern example

class Singleton { public:

static Singleton* Instance(); // gives back a real object! proof(void); // proof that the object was made protected:

Singleton(); // constructor private:

static Singleton* _singleton; };

In/Out Board

Displays the in/out status of users Displays the day and time when the users last

entered/left the room Web-based application User-defined services will be triggered upon user’s

entering / leaving. – Turn on / off the lights – Pull out the seat– Turn on and log in the user’s computer– Coffee will be served

Architecture Design

Client(Web Browser)

User Info DB(MS Access)

In/Out EventSimulator

HTTP

RMI Main Server(Java programs)

Web Server(Tomcat, JSP)

JDBC

RMI

Main Server Design -- Reactor Pattern

For demultiplexing and dispatching handles for synchronous events.

Also known as dispatcher, notifier. Used in

– CORBA ORBs– InterViews– Ericsson EOS Call Center Management System– ACE Framework

Main Server Design -- Reactor Pattern

Reactor Pattern

Handles: identify resources Synchronous Event Demultiplexer: blocks awaiting

events to occur on a set of Handles. Initiation Dispatcher: an interface for registering,

removing, and dispatching Event Handlers. Event Handler: specifies hook methods Concrete Event Handler: implements the hook

method, as well as the methods to process these events

Reactor Pattern – General Collaborations

Pro’s & Con’s

Separation of concerns Improve modularity, reusability Improve application portability Provides coarse-grained concurrency control Non-preemptive Hard to debug

User Interface

User Interface -- Event Simulator

Conclusions

Patterns are useful for developing and documenting software.

Patterns repositories have been set up for– Distributed systems– Database systems– Fault tolerant systems…

More exploration on context-aware applications

Questions?