Architectural Middleware

Copyright © Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy. All rights reserved.

Architectural Middleware

Eric M. DashofyCSCI 578 at the University of Southern

CaliforniaMarch 24, 2011

Software Architecture: Foundations, Theory, and Practice

Review: From Architecture to Design to Implementation

ProblemSpace

SolutionSpace

A D I


Mapping Architecture to Implementation There is a community who advocates Model-

Driven Architecture or Model-Driven Development Ideal: fully generate implementations

from architectural models This ideal is rarely feasible

Models are necessarily abstractionsof systems We can take the modeled

parts and map those,especially with domainknowledge

A

I

Limit/prevent architectural erosion


The Gap to Bridge Architecture Concepts

Application: Components, connectors, interfaces (at component level), high-level behaviors

Style: Connection rules, communication rules, concurrency rules…

Programming language concepts Functions, conditionals, variables, structures,

assignments, classes and objects… Operating system concepts

Threads, mutexes, sockets, files and filesystems, IPC mechanisms…


The Key Question How do we take architectural concepts and

realize them using the elements that we have in the implementation world?


A Discussion About MappingArchitectural Concept

Implementation Concepts

Components ?Connectors ?Interfaces ?Configurations ?Design Rationale ?Behavior ?Concurrency Rules ?NFPs ?


A Discussion About MappingArchitectural Concept

Implementation Concepts

Components Classes, packages, modules, …Connectors Software buses, middleware; others?Interfaces APIs, protocolsConfigurations Module dependencies, possibly supported

by reflectionDesign Rationale Comments, documentationBehavior Translated algorithmsConcurrency Rules Design patterns using OS-level concurrency

constructsNFPs Verified separately through testing,

inspections, etc.


Middleware, Frameworks, and Mappings (oh my!)

Middleware has a lot of broad definitions My definition: any software that sits in between

your application and your Programming Language/OS to provide services not provided by PL/OS

Architectural frameworksare a special typeof middleware

Application

Programming Language & OS

“Middleware”


So what’s the difference? There’s no clear, bright line

Middleware is designed based on services Architectural concerns are secondary

Frameworks are designed based on architectural styles and patterns Services are secondary


Traditional Middleware Traditional middleware may be based on services,

but it induces an architectural style (Di Nitto and Rosenblum)

Consider CORBA Services: Network transparency, language

transparency, OS transparency Induced properties: (primarily) synchronous

request-response point-to-point communication, hiding of network properties, OO-style topologies


Middleware is Everywhere Software reuse is alive and well, but perhaps

thriving most at the middleware layer Software systems today are increasingly built on

growing stacks of underlying middleware – whether we call it “Middleware” “Frameworks” “Component Libraries” “Toolkits”

All of it has architectural implications Who is really designing your software?


Let’s Discuss some Middleware “Distributed Systems Middleware”

DCE, Courier, CORBA, (D)COM(+), RMI, Web Services

Message-Oriented Middleware MQ Series, MSMQ, JMS implementations

“Enterprise Service Buses” Web Application Middleware

Server-side: JSP, Spring, JSF, Rich Faces, Rails, Grails, Pylons, TurboGears

Client-Side: YUI, JQuery, JQuery UI, Dojo, Prototype


Architecture Frameworks Start from an architectural style (or specific

architecture) Pipe-and-filter Web Services C2 Prism Myx

Develop middleware that supports (not necessarily enforces) the constraints of the style, tailored to support Desirable NFPs Additional desirable properties/services


A Tale of Four Frameworks Supporting the evolution of one system

(ArchStudio) over four versions. Through a fundamental change in architectural

style (C2Myx) Three research-based (Lightweight C2, Flexible

C2, Myx) One off the shelf (OSGi)


Review: C2 Style


Framework #1: Lightweight C2 Framework

16 classes, 3000 lines of code

Components & connectors extend abstract base classes

Concurrency, queuing handled at individual comp/conn level

Messages are request or notification objects

16Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; (C) 2008 John Wiley & Sons, Inc. Reprinted with permission.


Lightweight C2 Framework Advantages

Simple, small Control concurrency (or not) at brick level

Disadvantages Fixed top, bottom interfaces Potential for deadlock Single-inheritance limitation of Java


ArchStudio 2


Framework #2: Flexible C2 Framework

73 classes, 8500lines of code

Uses interfacesrather than baseclasses

Threading policyfor applicationis pluggable

Message queuing policy isalso pluggable

19

Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; (C) 2008 John Wiley & Sons, Inc. Reprinted with permission.


Framework #2: Flexible C2 Framework

20



Flexible C2 Framework Advantages

Ability to implement and change out message queuing, threading policies

…but it turned out not to matter However, it did enable the “Steppable Engine”

Reduced dependency on base classes Flexible interfaces permit non-C2-topologies Synchronous call support Fully serializable control interface

Disadvantages Complexity Performance Certain threading policies (e.g., shepherd threads)

difficult to implement


ArchStudio 3


The Myx Style Combines useful qualities of C2, Weaves

(C2) All communication through interfaces (C2) No assumption of shared

state (C2) Substrate Independence

Top, bottom interfaces, enforced layering

(C2) Asynchronous eventing (Weaves) Synchronous

invocations (Weaves) Connectors create

threading policy Relatively hard to deadlock


Myx: Synchronous Patterns

Direct Call With Proxy


Myx: Asynchronous Patterns

Downward Event Upward Event


Myx: Nifty Patterns


Framework #3: Myx Framework 62 classes, 2600 lines of code Minimal required support for brick classes Pluggable brick loaders Framework does not get

involved in anyinter-brickcommunication


<<interface>>

IMyxRuntime

<<interface>>

IMyxBrick

<<interface>>

IMyxProvidedServiceProvider

<<interface>>

IMyxRequiredServiceProvider

1

*

1

1

<<interface>>

IMyxContainer

1

*

<<interface>>

IMyxBrickLoader

<<interface>>

IMyxBrickFactory

1

creates*

1

*

<<interface>>

IMyxLifecycleProcessor+init()+begin()+end()+destroy()

1*

<<create>>


Myx Framework Advantages

Performance: all communication between bricks direct Library of reusable connectors Pluggable brick loaders permit operation in different

contexts This becomes important later

Can support non-Myx topologies Fully serializable control interface Flexible dynamism

Disadvantages Complexity (sorta) Monitorability


ArchStudio 4


Worlds are Mixing! OSGi and Myx Myx was developed as a general-purpose

architectural style But was specifically built to support ArchStudio

4 ArchStudio 4 was going to be built in Eclipse

Considered AS3+Myx but rejected Eclipse has its own framework (OSGi), inducing a

style


Simplified view of OSGi

Bundleclass class

Exposed Pkgsclass class

Bundleclass class




Bundleclass class


Bundleclass class




Bundleclass class


Bundleclass class




Bundleclass class


Bundleclass class



OSGi Why? Provide a system with deployable and

undeployable units With well-known, manageable lifecycles

Permit lazy loading of bundles Permit dynamism

In a limited way


Integration Attempt #1 (AS4)

Bundle (all exposed)


Handling the Master of the Universe problem

ArchEditxArchADT

ArchEditEclipseView

myx.fw architecture implementation framework

Eclipse framework

communication

Instantiates and controls

Instantiates and controlsEclipseLayer

MyxLayer


Approach #1: Evaluation (+) “Hatting” solution solves MOU problem

(-) But it’s a dirty dirty hack (+) Requires no Eclipse-specific code in Myx

framework (+) Otherwise works OK with Eclipse and permits

deploy/undeploy through the Eclipse Update system (-) But the unit of deployment is the whole app!



“Core” Bundleclass class

“Common” Bundle

class class


“Common” Bundle

class class




“Common” Bundle

class class


“Common” Bundle

class class


Approach #2: Evaluation (+) “Hatting” solution still solves MOU problem

(-) But it’s still a dirty dirty hack (+) Eclipse-specific code in Myx framework can

be written entirely as extensions in a separate bundle

(+) Deploy/undeploy at the level of an individual component/connector


Takeaways Middleware is Everywhere and Everyware

May have more influence on your architecture than you do!

Beware middleware that gives you enticing services, but does not improve your cognitive control over your system

Frameworks are tricky to build But well-built frameworks can substantially

reduce the burden on app developersConcurrency is an area where this can be

especially true


Takeaways (cont.) Efficient frameworks stay out of the way of inter-

component communication Component granularity matters for efficiency

The difficulty in elegantly merging an architecture framework with existing middleware is very high This may be the biggest barrier to the adoption

of strong architectural styles.


BACKUP CHARTS


Implementing Lunar Lander in C2 Framework: Lightweight

C2 framework Each component has its

own thread of control Components receive

requests or notificationsand respond with newones

Message routing followsC2 rules

This is a real-time, clock-driven version of Lunar Lander 45



Implementing Lunar Lander in C2 (cont’d) First: Clock component Sends out a ‘tick’ notification

periodically Does not respond to any

messages



Clock Component

47

import c2.framework.*;

public class Clock extends ComponentThread { public Clock() { super.create("clock", FIFOPort.class); }

public void start() { super.start();

Thread clockThread = new Thread() { public void run() { // Repeat while the application runs while (true) { // Wait for five seconds try { Thread.sleep(5000); } catch (InterruptedException ie) {}

//Send out a tick notification Notification n = new Notification("clockTick"); send(n); } } };



Clock Component

48


public class Clock extends ComponentThread{ public Clock(){ super.create("clock", FIFOPort.class); }

public void start(){ super.start();

Thread clockThread = new Thread(){ public void run(){ //Repeat while the application runs while(true){ //Wait for five seconds try{ Thread.sleep(5000); } catch(InterruptedException ie){}

//Send out a tick notification Notification n = new Notification("clockTick"); send(n); } } };

clockThread.start(); }

protected void handle (Notification n) { // This component does not handle notifications }

protected void handle (Request r) { // This component does not handle requests }}



Implementing Lunar Lander in C2 Second: GameState

Component Receives request to update

internal state Emits notifications of new

game state on requestor when state changes

Does NOT compute newstate Just a data store



GameState Component

50


public class GameState extends ComponentThread{

public GameState() { super.create("gameState", FIFOPort.class); }

// Internal game state and initial values int altitude = 1000; int fuel = 500; int velocity = 70; int time = 0; int burnRate = 0; boolean landedSafely = false;



GameState Component

51



public GameState(){ super.create("gameState", FIFOPort.class); }

//Internal game state and initial values int altitude = 1000; int fuel = 500; int velocity = 70; int time = 0; int burnRate = 0; boolean landedSafely = false;

protected void handle (Request r) { if (r.name().equals("updateGameState")) { // Update the internal game state if (r.hasParameter("altitude")) { this.altitude = ((Integer)r.getParameter("altitude")).intValue(); } if (r.hasParameter("fuel")) { this.fuel = ((Integer)r.getParameter("fuel")).intValue(); } if (r.hasParameter("velocity")) { this.velocity = ((Integer)r.getParameter("velocity")).intValue(); } if (r.hasParameter("time")) { this.time = ((Integer)r.getParameter("time")).intValue(); } if (r.hasParameter("burnRate")) { this.burnRate = ((Integer)r.getParameter("burnRate")).intValue(); } if (r.hasParameter("landedSafely")) { this.landedSafely = ((Boolean)r.getParameter("landedSafely")) .booleanValue(); } // Send out the updated game state Notification n = createStateNotification(); send(n); }



GameState Component

52



public GameState(){ super.create("gameState", FIFOPort.class); }

//Internal game state and initial values int altitude = 1000; int fuel = 500; int velocity = 70; int time = 0; int burnRate = 0; boolean landedSafely = false;

protected void handle(Request r){ if(r.name().equals("updateGameState")){ //Update the internal game state if(r.hasParameter("altitude")){ this.altitude = ((Integer)r.getParameter("altitude")).intValue(); } if(r.hasParameter("fuel")){ this.fuel = ((Integer)r.getParameter("fuel")).intValue(); } if(r.hasParameter("velocity")){ this.velocity = ((Integer)r.getParameter("velocity")).intValue(); } if(r.hasParameter("time")){ this.time = ((Integer)r.getParameter("time")).intValue(); } if(r.hasParameter("burnRate")){ this.burnRate = ((Integer)r.getParameter("burnRate")).intValue(); } if(r.hasParameter("landedSafely")){ this.landedSafely = ((Boolean)r.getParameter("landedSafely")) .booleanValue(); } //Send out the updated game state Notification n = createStateNotification(); send(n); }

else if (r.name().equals("getGameState")) { //If a component requests the game state //without updating it, send out the state

Notification n = createStateNotification(); send(n); } }

protected Notification createStateNotification() { // Create a new notification comprising the // current game state

Notification n = new Notification("gameState"); n.addParameter("altitude", altitude); n.addParameter("fuel", fuel); n.addParameter("velocity", velocity); n.addParameter("time", time); n.addParameter("burnRate", burnRate); n.addParameter("landedSafely", landedSafely); return n; } protected void handle (Notification n) { // This component does not handle notifications }}



Implementing Lunar Lander in C2 Third: GameLogic

Component Receives notifications of

game state changes Receives clock ticks

On clock tick notification,calculates new stateand sends request up



GameLogic Component

54


public class GameLogic extends ComponentThread { public GameLogic() { super.create("gameLogic", FIFOPort.class); }

// Game constants final int GRAVITY = 2;

// Internal state values for computation int altitude = 0; int fuel = 0; int velocity = 0; int time = 0; int burnRate = 0;

public void start() { super.start(); Request r = new Request("getGameState"); send(r); }



GameLogic Component

55


public class GameLogic extends ComponentThread{ public GameLogic(){ super.create("gameLogic", FIFOPort.class); }

//Game constants final int GRAVITY = 2;

//Internal state values for computation int altitude = 0; int fuel = 0; int velocity = 0; int time = 0; int burnRate = 0;

public void start(){ super.start(); Request r = new Request("getGameState"); send(r); }

protected void handle (Notification n) { if (n.name().equals("gameState")) { if (n.hasParameter("altitude")) { this.altitude = ((Integer)n.getParameter("altitude")).intValue(); } if (n.hasParameter("fuel")) { this.fuel = ((Integer)n.getParameter("fuel")).intValue(); } if (n.hasParameter("velocity")) { this.velocity = ((Integer)n.getParameter("velocity")).intValue(); } if (n.hasParameter("time")) { this.time = ((Integer)n.getParameter("time")).intValue(); } if (n.hasParameter("burnRate")) { this.burnRate = ((Integer)n.getParameter("burnRate")).intValue(); } }



GameLogic Component

56






protected void handle(Notification n){ if(n.name().equals("gameState")){ if(n.hasParameter("altitude")){ this.altitude = ((Integer)n.getParameter("altitude")).intValue(); } if(n.hasParameter("fuel")){ this.fuel = ((Integer)n.getParameter("fuel")).intValue(); } if(n.hasParameter("velocity")){ this.velocity = ((Integer)n.getParameter("velocity")).intValue(); } if(n.hasParameter("time")){ this.time = ((Integer)n.getParameter("time")).intValue(); } if(n.hasParameter("burnRate")){ this.burnRate = ((Integer)n.getParameter("burnRate")).intValue(); } }

else if (n.name().equals("clockTick")) { // Calculate new lander state values int actualBurnRate = burnRate; if (actualBurnRate > fuel) { //Ensure we don’t burn more fuel than we have actualBurnRate = fuel; }

time = time + 1; altitude = altitude - velocity; velocity = ((velocity + GRAVITY) * 10 – actualBurnRate * 2) / 10; fuel = fuel - actualBurnRate;

// Determine if we landed (safely) boolean landedSafely = false; if (altitude <= 0) { altitude = 0; if (velocity <= 5) { landedSafely = true; } }



GameLogic Component

57






protected void handle(Notification n){ if(n.name().equals("gameState")){ if(n.hasParameter("altitude")){ this.altitude = ((Integer)n.getParameter("altitude")).intValue(); } if(n.hasParameter("fuel")){ this.fuel = ((Integer)n.getParameter("fuel")).intValue(); } if(n.hasParameter("velocity")){ this.velocity = ((Integer)n.getParameter("velocity")).intValue(); } if(n.hasParameter("time")){ this.time = ((Integer)n.getParameter("time")).intValue(); } if(n.hasParameter("burnRate")){ this.burnRate = ((Integer)n.getParameter("burnRate")).intValue(); } }

else if(n.name().equals("clockTick")){ //Calculate new lander state values int actualBurnRate = burnRate; if(actualBurnRate > fuel){ //Ensure we don’t burn more fuel than we have actualBurnRate = fuel; }

time = time + 1; altitude = altitude - velocity; velocity = ((velocity + GRAVITY) * 10 – actualBurnRate * 2) / 10; fuel = fuel - actualBurnRate;

//Determine if we landed (safely) boolean landedSafely = false; if(altitude <= 0){ altitude = 0; if(velocity <= 5){ landedSafely = true; } }

Request r = new Request("updateGameState"); r.addParameter("time", time); r.addParameter("altitude", altitude); r.addParameter("velocity", velocity); r.addParameter("fuel", fuel); r.addParameter("landedSafely", landedSafely); send(r); } }

protected void handle (Request r) { //This component does not handle requests }}



Implementing Lunar Lander in C2 Fourth: GUI Component Reads burn rates from

user and sends themup as requests

Receives notifications ofgame state changes andformats them to console



GUI Component

59

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;


public class GUI extends ComponentThread{ public GUI() { super.create("gui", FIFOPort.class); }

public void start() { super.start(); Thread t = new Thread(){ public void run(){ processInput(); } }; t.start(); }



GUI Component

60



public class GUI extends ComponentThread{ public GUI(){ super.create("gui", FIFOPort.class); }

public void start(){ super.start(); Thread t = new Thread(){ public void run(){ processInput(); } }; t.start(); }

public void processInput() { System.out.println("Welcome to Lunar Lander"); try{ BufferedReader inputReader = new BufferedReader( new InputStreamReader(System.in));

int burnRate = 0; do { System.out.println("Enter burn rate or <0 to quit:"); try { String burnRateString = inputReader.readLine(); burnRate = Integer.parseInt(burnRateString);

Request r = new Request("updateGameState"); r.addParameter("burnRate", burnRate); send(r); } catch (NumberFormatException nfe) { System.out.println("Invalid burn rate."); } } while(burnRate >= 0); inputReader.close(); } catch (IOException ioe) { ioe.printStackTrace(); } }



GUI Component

61





public void processInput(){ System.out.println("Welcome to Lunar Lander"); try{ BufferedReader inputReader = new BufferedReader( new InputStreamReader(System.in));

int burnRate = 0; do{ System.out.println("Enter burn rate or <0 to quit:"); try{ String burnRateString = inputReader.readLine(); burnRate = Integer.parseInt(burnRateString);

Request r = new Request("updateGameState"); r.addParameter("burnRate", burnRate); send(r); } catch(NumberFormatException nfe){ System.out.println("Invalid burn rate."); } }while(burnRate >= 0); inputReader.close(); } catch(IOException ioe){ ioe.printStackTrace(); } }

protected void handle (Notification n) { if (n.name().equals("gameState")) { System.out.println(); System.out.println("New game state:");

if (n.hasParameter("altitude")) { System.out.println(" Altitude: " + n.getParameter("altitude")); } if (n.hasParameter("fuel")) { System.out.println(" Fuel: " + n.getParameter("fuel")); } if (n.hasParameter("velocity")) { System.out.println(" Velocity: " + n.getParameter("velocity")); } if (n.hasParameter("time")) { System.out.println(" Time: " + n.getParameter("time")); } if (n.hasParameter("burnRate")) { System.out.println(" Burn rate: " + n.getParameter("burnRate")); }



GUI Component

62





public void processInput(){ System.out.println("Welcome to Lunar Lander"); try{ BufferedReader inputReader = new BufferedReader( new InputStreamReader(System.in));

int burnRate = 0; do{ System.out.println("Enter burn rate or <0 to quit:"); try{ String burnRateString = inputReader.readLine(); burnRate = Integer.parseInt(burnRateString);

Request r = new Request("updateGameState"); r.addParameter("burnRate", burnRate); send(r); } catch(NumberFormatException nfe){ System.out.println("Invalid burn rate."); } }while(burnRate >= 0); inputReader.close(); } catch(IOException ioe){ ioe.printStackTrace(); } }

protected void handle(Notification n){ if(n.name().equals("gameState")){ System.out.println(); System.out.println("New game state:");

if(n.hasParameter("altitude")){ System.out.println(" Altitude: " + n.getParameter("altitude")); } if(n.hasParameter("fuel")){ System.out.println(" Fuel: " + n.getParameter("fuel")); } if(n.hasParameter("velocity")){ System.out.println(" Velocity: " + n.getParameter("velocity")); } if(n.hasParameter("time")){ System.out.println(" Time: " + n.getParameter("time")); } if(n.hasParameter("burnRate")){ System.out.println(" Burn rate: " + n.getParameter("burnRate")); }

if (n.hasParameter("altitude")) { int altitude = ((Integer)n.getParameter("altitude")).intValue(); if (altitude <= 0) { boolean landedSafely = ((Boolean)n.getParameter("landedSafely")) .booleanValue(); if (landedSafely) { System.out.println("You have landed safely."); } else { System.out.println("You have crashed."); } System.exit(0); } } } }

protected void handle (Request r) { //This component does not handle requests }}



Implementing Lunar Lander in C2 Lastly, main program Instantiates and connects

all elements of the system



Main Program

64


public class LunarLander {

public static void main(String[] args) { // Create the Lunar Lander architecture Architecture lunarLander = new SimpleArchitecture("LunarLander");

// Create the components Component clock = new Clock(); Component gameState = new GameState(); Component gameLogic = new GameLogic(); Component gui = new GUI();

// Create the connectors Connector bus = new ConnectorThread("bus");

// Add the components and connectors to the architecture lunarLander.addComponent(clock); lunarLander.addComponent(gameState); lunarLander.addComponent(gameLogic); lunarLander.addComponent(gui);

lunarLander.addConnector(bus);



Main Program

65


public class LunarLander{

public static void main(String[] args){ //Create the Lunar Lander architecture Architecture lunarLander = new SimpleArchitecture("LunarLander");

//Create the components Component clock = new Clock(); Component gameState = new GameState(); Component gameLogic = new GameLogic(); Component gui = new GUI();

//Create the connectors Connector bus = new ConnectorThread("bus");

//Add the components and connectors to the architecture lunarLander.addComponent(clock); lunarLander.addComponent(gameState); lunarLander.addComponent(gameLogic); lunarLander.addComponent(gui);

lunarLander.addConnector(bus);

// Create the welds (links) between components and // connectors lunarLander.weld(clock, bus); lunarLander.weld(gameState, bus); lunarLander.weld(bus, gameLogic); lunarLander.weld(bus, gui);

//Start the application lunarLander.start(); }}


Architectural Middleware

Documents

practice mapping architecture

practice middleware

modeldriven architecture

practice review

architectural styles

architectural concepts

architectural style

language transparency