Remote Pointcut - A Language Construct for Distributed AOP

AOSD'04, Lancaster, UK 1

Remote Pointcut- A Language Construct for Distributed AOP

Muga Nishizawa (Tokyo Tech, Japan)Shigeru Chiba (Tokyo Tech, Japan)

Michiaki Tatsubori (TRL, Japan IBM)


This Talk Our goal

To modularize crosscutting concerns in distributed software

Motivating problem AspectJ can separate them But, the implementation is NOT simple E.g. a test code for distributed software

Our solution Remote pointcut


Test Code for Distributed Authentication Service

Confirm addUser() is executed on Database when client remotely calls registerUser() Client calls registerUser(),

registerUser() calls addUser()

Authenticator

Database

registerUser()

Client

addUser()

Register a new user on a DB


Ideal Design for Test Code

On Client, 1. flag = false. 2. call registerUser() on Authenticator. 3. if addUser() is executed on Database,

then flag = true. 4. assert flag == true.

Authenticator

Database

registerUser()

addUser()

Client


Test Code in Java Crosscutting concern

Database code must be edited for test

1. Flag = false2. Call registerUser()

3. assert flag == true

class Database { void addUser() { invoke Callback … … add the user to the database } … …}

Client

Flag = true

Callback

Database

Authenticator

RMI (Remote Method Invocation)

Crosscutting concern


Test Code in Java and AspectJ

The concern is separated Database code is not edited

1. Flag = false2. Call registerUser()

3. Assert flag == true

Client

Flag = true

Callback

class Database { void addUser() {

… … add the user to the database }}

Database

aspect DatabaseTest { before(): execution(void addUser()){ invoke Callback }}

DatabaseTest

RMI


This Design is Not Satisfactory When writing the test code, we must consider two

concerns: Test Distribution

It requires to divide the code into three sub-modules Network processing (RMI) and deployment

1. flag = false.2. call registerUser() on Authenticator.

3. if addUser() is invoked on Database,

flag = true.

4. Assert flag == ture

Three distributed sub-modules

Don’t consider this!


Our Solution - Remote Pointcut

To identify join points in a program on a remote host To run advice on a different host from the host w

here join points are pointcut Like RMI for distributed OOP

class Database { void addUser() { … … }}

Remote pointcut

aspect Log { before() : execution(void addUser()) { System.out.println(“addUser”); }}

Identified join point


Test Code using a Remote Pointcut Test program is a single non-distributed module

Authenticator

1. flag = false2. call registerUser()

3. assert flag == true

before(): cflow(call(void registerUser()))&&execution(void addUser()){ flag = true}

call addUser()

Remote Pointcut

class Database { void addUser() {

} … …}

Database

AuthenticatorTest(Aspect)

call registerUser()


Test Code Implementationaspect AuthenticatorTest extends TestCase { boolean flag;

void testRegisterUser() { flag = false; String userId = "muga", password = "xxx"; Authenticator auth = (Authenticator) Naming.lookup("auth"); auth.registerUser(userId, password); assertTrue(flag); }

before(): // remote pointcut cflow(call(void Authenticator.registerUser())) && execution(void Database.addUser()) { flag = true; }}

When addUser() is executed, the flag is set to true

Confirms the flag is true

Calls registerUser()

Declares and initializes the flag


DJcutter - Distributed AOP Language

It’s an extension of AspectJ language Remote pointcut Remote inter-type declaration

Load-time weaving Aspect weaving in DJcutter is performed at loa

d-time


DJcutter Language Specification Pointcut

DJcutter provides pointcut designators in AspectJ Call, execution, within, target, …

Hosts(Host, …) The join points in execution on the hosts

Cflow(Pointcut) All join points that occur between the entry and exit of

each join point specified by Pointcut

Advice Before, after, and around


Remote Inter-type Declaration To declare methods and fields in classes

on a remote host

Database

aspect AuthenticatorTest { boolean Database.containsUser(String userId) { // If the user entry specified by userId is found // in the database. }}

boolean containsUser();

Append at load-timeAuthenticatorTest


Use of Remote Inter-type Declaration

aspect AuthenticatorTest extends TestCase {

void testRegisterUser() { String userId = "muga", password = "xxx"; Authenticator auth = (Authenticator) Naming.lookup("auth"); Database db = (Database) Naming.lookup(“db”); assertTrue(! db.containsUser(userId)); auth.registerUser(userId, password); assertTrue(db.containsUser(userId)); }

boolean Database.containsUser(String userId) { // If the user entry specified by userId is // found in the database. }}

Confirms that the user entry


DJcutter Implementation - Load-time Weaving

Aspect source file

Java bytecode

Compiler

Aspect ServerClass Loader

Class Loader

entry

Distributed software

Distributed software

weave

weave

deploy

deploy

Runtime InfrastructureRuntime Infrastructure

Runtime Infrastructure


Related Work 1

Middleware for automatic distribution E.g. J-Orchestra and Addistant They completely hide distribution concern Conbination of AspectJ and them

We are not sure they are good for Tomcat, Oracle, …


Related Work 2 Other distributed AOP languages

E.g. D language framework JAC (Java Aspect Componenets)

DADO To modularize functional crosscutting concerns

DJcutter Remote pointcut To modularize non-functional crosscutting con

cerns


Conclusion Remote pointcut

To transparently identify join points on remote hosts Like RMI for distributed OOP

To run advice on a different host from the host where join points are pointcut Without consideration of distribution concern

DJcutter – Distributed AOP Language Remote pointcut Extension of AspectJ language


The End

Thanks




Even if writing RMI is very easy,

We still have a question: Why the test code consists of three sub-modules? Because of not test but distribution concern



flag = true.


Design Problem


DJcutter Implementation

Compiler To generate a Java-bytecode representing an

aspect Runtime infrastructure

To implement load-time weaving Aspect server Extended class loader



Our Solution

To run advice on a different host from the host where join points are pointcut

Implementing a single module without consideration of distribution

That is, it can separate distribution concern from the test code Non-distributed sub-modules, Automatic deployment, And separation of crosscutting concerns


Remote Pointcut

To identify join points in a program flow on remote host transparently Corresponding to RMI for distributed OOP Extends to pointcut designators in AspectJ

A single non-distributed module on a single host

class Database { void addUser() { System.out.println(“addUser”); … … }}

Database

Remote pointcut

aspect Log { before() : execution(void addUser()) { System.out.println(“addUser”); }}

Log


Three Distributed Sub-modules Ideally, a concern should be described a non-distributed single module We want to write without consideration of distribution

The test code is written with consideration of distribution As a result, sub-modules, complicated network

processing, deployment



flag = true.



Three Distributed Sub-modules Idealy, a concern should be described as a non-dist

ributed single module on a single host この test code は、分散した sub-modules に

なっている Separated, but far from the ideal test code Remote method invocation among sub-modules Deployment

Client

Callback

DatabaseTest

RMI

DatabaseTest

ClientCallback

DatabaseTest


Related Work


Ideal Test Code In the test code, we declare a flag for comfirming t

hat addUser() was executed

AuthenticatorTest Program call registerUser()

1. Sets flag to false2. Remotely calls registerUser()

3. Confirms that flag is ture

Flag is set to true, when addUser() is executed

Main part for testingcall addUser()

class DbServer { void addUser() { … … }}

Database


実際に実装するAuthServer

DbServer

AuthServerTest 1.registerUser() 呼出

2.addUser() 呼出

class AuthServerTest extends TestCase {

boolean wasAddUserCalled; void testRegisterUser() { Naming.rebind("test", new RecieverImpl()); wasAddUserCalled = false; String userId = "muga", password = "xxx"; AuthServer auth = (AuthServer) Naming.lookup("auth"); auth.registerUser(userId, password); assertTrue(wasAddUserCalled); }class ReceiverImpl extends UnicastRemoteObject implements NotificationReceiver {

void confirmCall() { wasAddUserCalled = true; } }interface NotificationReceiver { void confirmCall(); }

interface NotificationReceiver { void confirmCall(); }

aspect Notification { before(): execution(void DbServer.addUser()){ NotificationReceiver test = (NotificationReceiver) Naming.lookup("test"); test.confirmCall(); }}

RMI


Experimental Results

Documents

Remote Pointcut - A Language Construct for Distributed AOP