Reading C2-style Applications Built in c2.fw

1
Reading C2-style Applications Built in c2.fw

• Eric M. Dashofy
• edashofy_at_ics.uci.edu
• For ICS 52
• October 20, 2004

2
Overview

• Software architectures
• The C2 architectural style
• With live example
• The Klax application

3
Software Architecture Basic Elements
Interfaces
Clock
Component
Connector
Bus1
Interfaces
4
Software Architecture Basic Elements (cont).
Clock
Configuration
Links
Bus1
LCD Driver
5
An Architectural Style

• One definition of an architectural style
• An architectural style is a named set of
  constraints (e.g., rules) you put on your
  development
• Constraints may be topological, behavioral,
  communication-oriented, you name it
• This can complicate development because these
  constraints may be inconvenient or unfamiliar
• BUT architectural styles elicit beneficial system
  properties that would be really hard to get
  otherwise

6
Examples from building architecture

1. Name some constraints in each style
2. Name some benefits (-ilities) elicited by each
   style.

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The C2 Architectural Style

• Topological Constraints
• All components, connectors have two interfaces,
  top and bottom
• Components can be connected to 0-1 connector on
  each interface
• Connectors can be connected to 0 components or
  connectors on each interface

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The C2 Architectural Style

• Communication Constraints
• Components connectors communicate using only
  independent events or messages
• Requests go up (requests rise)
• Notifications go down
• No passing pointers
• Components connectors communicate
  asynchronously
• Can send/receive events at any time
• No blocking!

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The C2 Architectural Style

• Dependency Constraints
• Components may make assumptions about services
  provided above them
• But not who is providing them
• Components may NOT make assumptions about
  services provided below them
• Concurrency Constraints
• Each component connector assumes its running
  in its own thread of control

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Live Example
Data Store
GUI Interpreter
Alarm
GUI
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Live Example
Data Store
Stores data emits notifications whenever data
changes.
GUI Interpreter
Alarm
GUI
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Live Example
Interprets basic GUI actions translates them
into data store operations
Data Store
GUI Interpreter
Alarm
GUI
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Live Example
Data Store
Rings a bell whenever value of X changes
GUI Interpreter
Alarm
GUI
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Live Example
Data Store
GUI Interpreter
Alarm
Accept process user actions
GUI
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Live Example
Data Store
GUI Interpreter
Alarm
Bus connector routes messages
GUI
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Live Example
Data Store
GUI Interpreter
Alarm
GUI
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What ilities does C2 buy us?

• What do you think?

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-ilities bought by C2

• Flexibility
• Loose coupling lets you swap out components,
  interpose components
• Flexible connectors allow run-time changes
• Distributability
• Since no assumption of shared address space,
  distributing an app across machines is easy
• Visibility
• Since all messages go through connectors, they
  are easy to catch and log
• Parallelizability
• One-thread-per-brick means multiprocessor
  machines are effectively utilized

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Event-based vs. OO

• Event-based
• Communication by events
• Mostly asynchronous
• Requests emitted to unknown parties
• Responses and state changes go to many parties
• No shared pointers

• Object Oriented
• Communication by procedure calls
• Mostly synchronous
• Requests emitted to named party only
• Responses to caller only, state changes to many
• Lots of shared pointers

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Implementing a C2 architecture
C2 architecture
Event-basedWorld
Implemented by
Application (implemented)
???
How do we bridge this gap?
Java/JVM
Object-orientedWorld
Uses services provided by
Native OS
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Implementing a C2 architecture
C2 architecture
Event-basedWorld
Implemented by
Application (implemented)
Uses services provided by
Architecture Framework
Uses services provided by
Java/JVM
Object-orientedWorld
Uses services provided by
Native OS
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Whats an architecture framework?

• An architecture framework is software that helps
  to bridge the gaps between an architectural style
  and a particular implementation platform.

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Example

• C2 World
• Components
• Connectors
• Events
• Links
• Many threads
• Asynchronous communication

• Java World
• Objects
• Method calls
• Parameters
• References
• Few threads
• Synchronous communication

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Enter c2.fw

• c2.fw is an architecture framework for the C2
  style built in Java, providing
• Abstract base classes for components, connectors
• Reusable connectors (local network)
• (Pluggable) topology management
• (Pluggable) message queuing policies
• (Pluggable) threading policies
• Essentially, c2.fw does the hard work, components
  and connectors simply implement behaviors.

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What does a message look like?

• In c2.fw, a message can be any serializable (e.g.
  no pointers) object
• NamedPropertyMessages (or subclasses) are popular
  though
• Have a String name
• Plus a set of name-value pairs
• e.g. description, Rectangle 1
• e.g. width, 123
• e.g. color, java.awt.Color.BLACK

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Reading a c2.fw application

• Basic format
• Lifecycle methods
• init(), begin(), end(), destroy()
• start(), stop(), suspend(), resume()
• Handling messages
• void handle(Message m)
• Sending messages
• sendToAll(Message m, Interface i)

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Your basic c2.fw component
package edu.uci.ics.mypackageimport c2.fw.
//import c2.fw packageimport c2.legacy.
//import support for 2-interface
//C2 components
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Your basic c2.fw component
package edu.uci.ics.mypackageimport c2.fw.
//import c2.fw packageimport c2.legacy.
//import support for 2-interface
//C2 componentspublic class MyC2Component
extends AbstractC2Brick
Implements lots of boilerplate functionality from
the base c2.fw.Brick interface declares a top
interface topIface and a bottom interface
bottomIface.
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A boilerplate c2.fw component
package edu.uci.ics.mypackageimport c2.fw.
//import c2.fw packageimport c2.legacy.
//import support for 2-interface
//C2 componentspublic class MyC2Component
extends AbstractC2Brick public
MyC2Component(Identifier id) super(id)

Each component or connector has a unique
identifier.
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A boilerplate c2.fw component
package edu.uci.ics.mypackageimport c2.fw.
//import c2.fw packageimport c2.legacy.
//import support for 2-interface
//C2 componentspublic class MyC2Component
extends AbstractC2Brick public
MyC2Component(Identifier id) super(id)
public void begin() //called automatically
by fw. //send out initial events
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Lifecycle Methods
public void init() //called when
component/connector is created //but component
not guaranteed to be hooked up public void
begin() //called when component/connector is
hooked up //in the architecture, should send
initial messages public void end() //called
when component/connector is about to be
//unhooked, should send final messages public
void destroy() //called when
component/connector is about to be //destroyed
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A boilerplate c2.fw component
package edu.uci.ics.mypackageimport c2.fw.
//import c2.fw packageimport c2.legacy.
//import support for 2-interface
//C2 componentspublic class MyC2Component
extends AbstractC2Brick public
MyC2Component(Identifier id) super(id)
public void begin() //called automatically
by fw. //send out initial events
public void handle(Message m) //handle
message
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Implementing handle()
//handle() method for our hypothetical alarm
component //Called automatically when component
receives a message //Should ring bell whenever
value of X changes public void
handle(Message m) //handle message
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Implementing handle()
//handle() method for our hypothetical alarm
component public void handle(Message m)
//handle message if(m instanceof
NamedPropertyMessage) NamedPropertyMessage
npm (NamedPropertyMessage)m
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Implementing handle()
//handle() method for our hypothetical alarm
component public void handle(Message m)
//handle message if(m instanceof
NamedPropertyMessage) NamedPropertyMessage
npm (NamedPropertyMessage)m String name
npm.getName() if((name ! null)
(name.equals(valueChanged))
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Implementing handle()
//handle() method for our hypothetical alarm
component public void handle(Message m)
//handle message if(m instanceof
NamedPropertyMessage) NamedPropertyMessage
npm (NamedPropertyMessage)m String name
npm.getName() if((name ! null)
(name.equals(valueChanged)) String
varName (String)npm.getParameter(varName)
if((varName ! null) (varName.equals(x))

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Implementing handle()
//handle() method for our hypothetical alarm
component public void handle(Message m)
//handle message if(m instanceof
NamedPropertyMessage) NamedPropertyMessage
npm (NamedPropertyMessage)m String name
npm.getName() if((name ! null)
(name.equals(valueChanged)) String
varName (String)npm.getParameter(varName)
if((varName ! null) (varName.equals(x))
ringBell()
NamedPropertyMessage rnpm new
NamedPropertyMessage(AlarmFired)
rnpm.addProperty(time,
System.currentTimeMillis())
sendToAll(rnpm, bottomIface)

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Implementing handle()
If we care, we could have checked what interface
that message came in on if(m.getDestination().g
etInterfaceIdentifier().equals(
AbstractC2Brick.TOP_INTERFACE_ID)) //its a
notification