1. Aspect Oriented Software Design
Therapon Skotiniotis Karl Lieberherr
Northeastern University
Boston, MA USA
5/24/2019
ABB Workshop

2. The talk will cover .. The problem The solution The benefits
“code tangling”
The solution
Better abstractions to provide advanced “Separation of Concerns”
The benefits
Higher code modularity
Better code reuse
Ease of program extensions/maintenance/understanding
5/24/2019
ABB Workshop

3. The problem Readers Writers Protocol Multiple Readers Single Writer
class Book:
// data
Book() {Message = new StringBuffer("null");}
public int write (String msg, int ip) {
if ((ip % 10) > 0) return 0;
else if (AuthClients < MaxAuthClients) {
AuthClients++;
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
if (getWWriters() == 0) {
Message.replace(0, Message.length(), msg); }
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify();
decrAWriters();
synchronized (AuthQueue) {
AuthClients--;
AuthQueue.notify();
return 1;
else synchronized (WQueue) {
WQueue.wait();
else synchronized (AuthQueue) {
AuthQueue.wait();
} }
Readers Writers Protocol
Multiple Readers
Single Writer
Waiting Writers get priority
Authentication required
Enforcing the requirements
Authentication
Synchronization
Scheduling
Functionality
5/24/2019
ABB Workshop

4. Concerns and their Separation
In Readers Writers
Functionality
read(), write()
Authentication
Yes, no
Synchronization
Resource available or not
Scheduling
Policy on who has priority to go next
5/24/2019
ABB Workshop

5. Concerns and their Separation (cont)
In Readers Writers
Functionality
read(), write()
Authentication
Yes, no
Synchronization
Resource available or not
Scheduling
Policy on who has priority to go next
Operation
System Constraints
5/24/2019
ABB Workshop

6. Concerns and their Separation (cont)
In OOP, functional decomposition
has been performed along one
dimension: component.
Crosscutting concerns are not
random properties
Systematically repeated at different
points within your code
Affect the semantics and/or
performance of your system
AOSD proposes the means to encapsulate
crosscutting concerns
objects
aspects
5/24/2019
ABB Workshop

7. Concerns and their Separation (cont)
“Separation of Concerns” [Parnas 72] drives software development.
A concern is a concept, realized as a unit of software.
Each concern is addressed separately in isolation
Each concern becomes a module keeping inter-module dependencies to the minimum
“Do not talk to strangers” The Law Of Demeter
There is no established methodology on how to achieve this principle.
5/24/2019
ABB Workshop

8. From this … Authentication Synchronization Scheduling Functionality
class Book:
// data
Book() {Message = new StringBuffer("null");}
public int write (String msg, int ip) {
if ((ip % 10) > 0) return 0;
else if (AuthClients < MaxAuthClients) {
AuthClients++;
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
if (getWWriters() == 0) {
Message.replace(0, Message.length(), msg); }
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify();
decrAWriters();
synchronized (AuthQueue) {
AuthClients--;
AuthQueue.notify();
return 1;
else synchronized (WQueue) {
WQueue.wait();
else synchronized (AuthQueue) {
AuthQueue.wait();
} }
Authentication
Synchronization
Scheduling
Functionality
5/24/2019
ABB Workshop

9. … to this synchronized (AuthQueue) { Authentication Synchronization
if (getWWriters() == 0) { }
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
class Book:
// data
Book() {Message = new StringBuffer("null");}
public int write (String msg, int ip) {
Message.replace(0, Message.length(), msg);
return 1; }
if ((ip % 10) > 0) return 0;
else if (AuthClients < MaxAuthClients) {
AuthClients++;
synchronized (AuthQueue) {
AuthClients--;
AuthQueue.notify(); }
else synchronized (AuthQueue) {
AuthQueue.wait();
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
Authentication
Synchronization
Scheduling
Functionality
5/24/2019
ABB Workshop

10. Concerns and their Separation (cont)
if (getWWriters() == 0) { }
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
class Book:
// data
Book() {Message = new StringBuffer("null");}
public int write (String msg, int ip) {
Message.replace(0, Message.length(), msg);
return 1; }
if ((ip % 10) > 0) return 0;
else if (AuthClients < MaxAuthClients) {
AuthClients++;
synchronized (AuthQueue) {
AuthClients--;
AuthQueue.notify(); }
else synchronized (AuthQueue) {
AuthQueue.wait();
Aspect
Base
Aspect
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
Authentication
Synchronization
Scheduling
Functionality
Aspect
5/24/2019
ABB Workshop

11. Putting it all together
The program needs to maintain the overall problem/solution semantics
Code in aspects is only to be executed at specific execution points
Control (ordering) at this execution points matters
JoinPoint Model
Provides the means to identify points within the execution to which aspectual code can be executed
Weaving: Underlying AOSD tool performs the integration
At JoinPoints as specified by your code
Attaching code as specified by your Aspect
The “mechanics” behind the JoinPoint make all the difference
Static Vs Dynamic
Expressiveness of JoinPoint definition language
Aspect Code scope and execution capabilities
5/24/2019
ABB Workshop

12. Concerns and their Separation (cont)
public int write (String msg, int ip) {
before:
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
after:
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
before:
if (getWWriters() == 0) {
return true; }
after:
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
before:
if (ip %10 == 0) { … }
after:
authenticated --;
5/24/2019
ABB Workshop

13. Concerns and their Separation (cont)
pointcut: call(Book.write(…));
public int write (String msg, int ip) {
before:
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
after:
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
before:
if (getWWriters() == 0) {
return true; }
after:
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
before:
if (ip %10 == 0) { … }
after:
authenticated --;
5/24/2019
ABB Workshop

14. Concerns and their Separation (cont)
JoinPoint
pointcut: call(Book.write(…));
public int write (String msg, int ip) {
before:
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
after:
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
before:
if (getWWriters() == 0) {
return true; }
after:
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
before:
if (ip %10 == 0) { … }
after:
authenticated --;
5/24/2019
ABB Workshop

15. Concerns and their Separation (cont)
pointcut: call(Book.write(…));
public int write (String msg, int ip) { 1
before:
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
after:
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
before:
if (getWWriters() == 0) {
return true; }
after:
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
before:
if (ip %10 == 0) { … }
after:
authenticated --;
5/24/2019
ABB Workshop

16. Concerns and their Separation (cont)
pointcut: call(Book.write(…));
public int write (String msg, int ip) { 2
before:
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
after:
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
before:
if (getWWriters() == 0) {
return true; }
after:
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
before:
if (ip %10 == 0) { … }
after:
authenticated --;
5/24/2019
ABB Workshop

17. Concerns and their Separation (cont)
pointcut: call(Book.write(…));
public int write (String msg, int ip) { 3
before:
if ((getAReaders() == 0) && (getAWriters() == 0)) {
if(getWWriters() > 0 )
decrWWriters();
incrAWriters();
else if (getWReaders() > 0)
synchronized (ReadQueue){
ReadQueue.notify(); }
after:
decrAWriters();
else synchronized (WQueue) {
WQueue.wait();
before:
if (getWWriters() == 0) {
return true; }
after:
if (getWWriters() > 0)
synchronized (WQueue) {
WriteQueue.notify();
before:
if (ip %10 == 0) { … }
after:
authenticated --;
5/24/2019
ABB Workshop

18. Terminology Aspect JoinPoint Model
Encapsulation of an aspect as a software entity
Includes code “Advice” to be executed at specific “PointCuts”
Types of advice
Before
After
Around
JoinPoint Model
A means to specify PointCuts
PointCuts are sets JoinPoints
JoinPoint: a point within the execution of your base system
Specification of PointCuts can be based on
Dynamic program information [ known at runtime]
Static program information [known at compile time]
5/24/2019
ABB Workshop

19. Aspect – Aspect Interaction
Dependence of Aspectual behavior
Orthogonal
No dependence between aspects (Logging and Scheduling)
Non-Orthogonal
Dependence between aspects (Synchronization and Scheduling)
Orthogonal aspects “play” nice
Non-orthogonal aspects hinder a protocol between them
Reuse requires all related dependent aspects
Alterations in aspects should maintain the dependence protocol
Alteration of the protocol may require code alterations throughout all affected aspects
5/24/2019
ABB Workshop

20. Benefits Better abstractions to capture crosscutting concerns
Separate development
Easier means for program extensibility and evolution
Higher potential for reuse
Better software quality
Easier to reason about program behavior
Closer to Program Design
PointCuts can be viewed as a generalization of Aspect/Object interactions
Separation between
Functional decomposition (OOP)
Cross-cutting Concerns ( Aspects)
Evolution towards “Plug-and-Play” Software Components and Components of the Shelf (COTS)
Non-invasive program reconfiguration, adaptation, evolution
5/24/2019
ABB Workshop