AspectWerkz 2 -and the road to AspectJ™ 5

Jonas BonérSenior Software Engineer

BEA Systems

• Overview• Plain Java™ AOP• Integration • Dynamicity• Extensible Aspect Container• AW Bench

Outline

Overview

• Plain Java™ AOP (syntax is JLS compatible)• Annotation-defined aspects• Integrates well in J2EE environments• Load time, runtime and static weaving• Runtime deployment and undeployment of aspects• Open Source, founded Q4 2002• Performance is comparable to ~ AspectJ™ -XnoInline• Extensible Aspect Container

Overview

• Pointcuts call(..), execution(..), set(..), get(..), cflow(..),

cflowbelow(..), handler(..), staticinitialization(..), within(..), withincode(..), hasfield(..), hasmethod(..), args(..), this(..), target(..)

• Life-cycle singleton, perthis(..), pertarget(..), perclass(..),

percflow(..)

• Intertype declarations (ITD) through Mixins (interface + methods implementing this interface)

• Pointcut pattern language very similar to AspectJ™: <annotation>* <modifier>* <type> <type>.<name>(<type>*)

Plain Java AOP

• JLS compatible• Annotation-defined aspects

– Java 5 @Annotation(…)– Java 1.3/1.4 /** @Annotation(…) */

• Benefits– Does not break IDEs, tools etc.– Gives the impression of flattening out the learning curve

(psychological effect)

• Drawbacks:– JLS compatibility: can not break type-checking, f.e. ITDs– Less elegant and concise syntax

Code-style defined aspect -AspectJ 5

import foo.bar.Baz;

aspect AsynchAspect { private ExecutorService m_threadPool = ...

void around(): execution(void Baz.*(..)) { m_threadPool.execute(new Runnable() { public void run() { try { // proceed the execution in a new thread proceed(); } catch (Throwable e) { // handle exception } } ); } }

Plain Java AOP

@Aspect class AsynchAspect { private ExecutorService m_threadPool = ...

@Around(“execution(void foo.bar.Baz.*(..))”) void execute(JoinPoint jp) throws Throwable { m_threadPool.execute(new Runnable() { public void run() { try { // proceed the execution in a new thread jp.proceed(); } catch (Throwable e) { // handle exception } } ); } }

Annotation-defined aspect - AspectWerkz Plain Java AOP

@Aspect class AsynchAspect { private ExecutorService m_threadPool = ...

@Around(“execution(void foo.bar.Baz.*(..))”) void execute(ProceedingJoinPoint jp) throws Throwable { m_threadPool.execute(new Runnable() { public void run() { try { // proceed the execution in a new thread jp.proceed(); } catch (Throwable e) { // handle exception } } ); } }

Annotation-defined aspect - AspectJ 5 Plain Java AOP

pointcut transactedOps() : execution(public void Account.credit(..)) || execution(public void Account.debit(..)) || execution(public void Customer.setAddress(..)) || execution(public void Customer.addAccount(..)) || execution(public void Customer.removeAccount(..));

Annotation-driven AOPPlain Java AOP

• Annnotion-based pointcuts can – Raise the abstraction level – Be more robust and predictable– Rely on standard annotations

• EJB 3, JSR-250, JSR-181

pointcut transactedOps() : execution(@Transactional * *.*(..));

• Challenges1. Allow the user to have strong typed direct access

to parameter values 2. Should be able to pass them on in the

proceed(..) without wrapping them3. Performance comparable with AspectJ™ 1.2

ChallengesPlain Java AOP

• Solutions1. Use args(..) for parameter access2. Custom proceed: user defines a custom JoinPoint interface

and defines his own proceed(..)3. Implementation of the interface is generated on the fly

public interface MyJP extends JoinPoint { Object proceed(long[] l, String s);}

@Around(..)Object advice(MyJP jp, long[] l, String s) { ... // modify the values return jp.proceed(l, s);}

ChallengesPlain Java AOP

Integration

• Load time weaving• Deployment modules (aop.xml)• Proxy based weaving• XML-based pointcut definitions

Load-time weaving

• Classes are weaved when loaded• Pre Java 5

– JRockit™ pre-processor– Class loader patching (credit to JMangler)

• Standardized in Java 5– JVMTI (agents)

• Implemented in AspectJ™ 5– Java 5 using JVMTI agent– Java 1.3/1.4 using JRockit™ pre-processor

Integration

Deployment modules

• Need to control which aspects are used in which module (class loader)– Include or exclude aspects higher up in class

loader hierarchy (or in my own module)

=> need for an AOP ‘deployment descriptor’

• Enabled through the aop.xml file• Is put in the META-INF directory in a JAR,

WAR or EAR file• Implemented in AspectJ™ 5

Integration

Proxy-based weaving

• Create a proxy

Target target = (Target)Proxy.newInstance( Target.class

);

• Proxy for target class is created (on the fly) and weaved before returned

• The target instance will now be advised by all the matching aspects (that are found in the class hierarchy)

• Implemented for AspectJ™ 5

Integration

Proxy-based weaving

• Benefits– Very transparent and lightweight– Same performance as static weaving (much

better than all other proxy implementations)– Same aspects and pointcuts can be used – no need for using Type+ etc.– Good enough in many situations in J2EE

environments• Drawbacks

– Only ‘method execution’ pointcuts– Can not advise:

•final methods•private methods

Integration

XML-based pointcut definitions

• AspectWerkz allows defining the whole aspect in XML (aop.xml)– Is very widely used by users– Had many benefits (f.e. no extra compilation step)– Powerful

• Drawbacks– Sometimes too powerful– Error prone– Hard to keep consistent semantics

• Solved in a better way in AspectJ™ 5– More restricted but guarantees consistent semantics– Still does what most users want; provide definition for

abstract pointcuts (e.g. “late binding”)

Integration

Sample: XML-based pointcut definitions

• Allows extending an abstract aspect• Needs to provide definition for all abstract

pointcuts

<aspectj> <aspects> <concrete-aspect name=“myaspects.DeploymentTimeAspect”

extends=“lib.AbstractLibraryAspect”> <pointcut name=“abstractPointcut” expression=“within(com.biz..*)”/> </concrete-aspect> </aspect></aspectj>

Integration

Dynamicity

• Runtime deployment of aspects (runtime weaving)

• Programmable per-instance deployment of aspects

Runtime weaving

• ”Hot” deployment and undeployment of aspects

• Based on HotSwap API• Atomic ’change sets’• Support for rollback• Resulting code is staticallly woven

Dynamicity

Sample: Runtime weaving

public void enableMonitoring() { Deployer.deploy(ResponseTimeAspect.class);

}

public void disableMonitoring() { Deployer.undeploy(ResponseTimeAspect.class);

}

public void enableMonitoring(String pointcut) { String xmlDef = "<aspect>" + "<pointcut name=‘toMonitor' expression='" + pointcut + "'/></aspect>"; Deployer.deploy(ResponseTimeAspect.class, xmlDef); }

Dynamicity

Challenges

• Same performance for runtime deployed aspects as for regularly woven aspects

• Zero overhead for target code after an aspect has been undeployed

• Ensure consistent and atomic aspect deployments– At specific join point – “all or nothing”

Dynamicity

Architecture

1. JoinPoint abstraction – Generated at runtime– Contains all data and logic for this join point– Has a public method:

public static final invoke(…){…}

– Inlined by VM– Also functions as the “closure” for around advice (can hold state

etc.)

2. Weave in a call to this static method in the target class (replaces the join point “code block”)

3. Can swap the logic in the JoinPoint without affecting the target class

Dynamicity

Limitations

• HotSwap limitations: – New methods can not be added at runtime

(supported in spec. but currently not in any impl.)

– Means that execution pointcuts for around advice needs to be prepared (we add empty method)

• Need wrapper methods to access private methods and fields in target class

Dynamicity

Programmable per-instance deployment

• Advice can be added to specific instance– Runtime deployment – Is pure per-instance (always ”this” instance)

• Target classes must be ‘prepared’ – set to implement the Advisable interface

• Credit to JBoss AOP

• Drawbacks– Introduces a new API

Dynamicity

Sample: Programmable per-instance deployment

• Prepare the classes you might want to advise later

<advisable pointcut-type="call|execution|set|get" expression="within(com.biz..*)"/> • Add advice to a specific instance (only) at runtime

POJO pojo = new POJO();

((Advisable) pojo).aw_addAdvice( "execution(@javax.ejb.TransactionAttribute)", new BeforeAdvice() { public void invoke(JoinPoint jp) { // start a new transaction } } );

Dynamicity

Aspects.aspectOf(TxAspect.class).beginTx(jp);

Extensible aspect container

• Pluggable weaver• Support for different ’aspect models’• Reference implementation supports

– AspectWerkz– Spring AOP– AOP Alliance– AspectJ™ (not complete)

• Dynamicity etc. to all aspect models• Weaver implementations

– ASM– Javassist– JRockit™ VM weaving (prototype)

Overview

Architecture overviewExtensible aspect container

Discussion

• Why did we implement it?1. Proof of concept for the merge with

AspectJ™

2. To ensure correct semantics when different frameworks co-exist (aspect precedence etc.)

3. To give (almost) equally good performance for all the ‘aspect models’

Extensible aspect container

Performance

• Spring aspects are executed – up to 13 times faster when running in the aspect container– Similar for all proxy based implementations

• AspectJ™ aspects are executed– from equally fast (before/after/non-inlined around)– to 6 times slower (inlined around)

• For details see the AW Bench microbenchmark suite

Extensible aspect container

Benefits for AspectJ users

• Production stable load-time weaving– Implemented in AspectJ™ 5

• Runtime deployment of aspects• Can reuse old AspectJ™ pointcut libraries

Extensible aspect container

AW Bench

• Compares the performance of major (industrial) AOP implementations

– AspectJ, AspectWerkz, JBoss AOP, JAsCo, Spring, dynaop, cglib proxy

• Currently tests:– All advice types (not ITDs)– Different kinds of context exposure (reflective and static)– execution pointcuts and singleton aspects only

• Please contribute – with tests and/or new frameworks

• More info: – http://docs.codehaus.org/display/AW/AOP+Benchmark

Micro-benchmark suite

Links

• Project home pages:– http://aspectwerkz.codehaus.org/– http://eclipse.org/aspectj/

• Articles:– http://www.theserverside.com/articles/article.tss?l=AspectWerkzP1– http://www.theserverside.com/articles/article.tss?l=AspectWerkzP2

• Benchmark:– http://docs.codehaus.org/display/AW/AOP+Benchmark

• AspectJ™ 5 FAQ:– http://dev.eclipse.org/viewcvs/indextech.cgi/~checkout~/aspectj-home/

aj5announce.html

• JRockit™ home page:– http://commerce.bea.com/products/weblogicjrockit/5.0/jr_50.jsp

Questions...?

Thanks for listening