abc :the AspectBench Compilerfor AspectJ Oege de Moor

Programming Tools GroupUniversity of Oxford

Joint work with: Chris Allan, Pavel Avgustinov, Sascha Kuzins, Neil Ongkingco, Damien Sereni, Ganesh Sittampalam, Julian Tibble (Oxford), Laurie Hendren, Jennifer Lhoták, Ondřej Lhoták, Bruno Dufour, Christopher Goard, Clark Verbrugge (McGill), Aske Simon Christensen (Aarhus)

What is AspectJ?

Disciplined Metaprogramming

Bluffer’s guide to aspect-lingoStatic: inject new members into existing

classes at compile-time

Dynamic: aspects observe composite events in

base program; run extra code at

begin/end of certain events

joinpoint = composite event = node in generalised dynamic call graph

pointcut = pattern of events = set of nodes in call graph

advice = extra code

shadow = program point that corresponds to joinpoint

Events, joinpoints and adviceProgram:

int x;void f() { x = x+1;}

execute:

… f(); …

events: begin/end joinpoints: boxes

begin call f();

begin execution f();

begin get x; end get x;

begin set x; end set x;

end execution f();

end call f();Advice can be run: before a joinpoint (immediately following “begin” event) after a joinpoint (immediately preceding “end” event) around a joinpoint (replacing whole contents of box between begin/end)

Example aspects

AspectJ: extension of Java

No allocations with “new” in inner loopaspect NoNewInRound { private int allocations;

before() : call(* World.play(..)) { allocations = 0; }

before() : cflow(call(* World.play(..))) && call(*.new(..)) &&

!within(NoNewInRound) { System.err.println("alloc at: "+ thisJoinPoint.getSourceLocation()); allocations++; }

after() : call(* World.play(..)) { if (allocations > 0) System.err.println("allocations per game "+allocations); }}

Memoisation

aspect Memo {Hashtable table;

pointcut toMemo() : call(Integer ackermann(Integer));

before() : toMemo() && !cflowbelow(toMemo()) {table = new Hashtable();

}

Integer around(Integer n) : toMemo() && args(n) { Integer entry = (Integer) table.get(n);

if (entry == null) { entry = proceed(n); table.put(n, entry);

} return entry; } }

Observing an oblivious subjectaspect Observe {

List Subject.observers = new ArrayList();

after(Subject s) returning(Observer o) :call(Observer.new(..)) && args(s) {

s.observers.add(o);}

after(Subject s) : call(* Subject.update(..)) && target(s) {for (Iterator obsit = s.observers.iterator(); obsit.hasnext(); ) {

Observer o = (Observer) obsit.next();o.refreshView();

}}

}

AOP languages: summary

Conceptual model:traces of (composite) events at runtime

Pointcuts: query language for events

Advice:run extra code before/after/aroundselected events

Compiling AspectJ

Match events at compile timewhenever possible: “weaving”

AspectJ compilers

ajc: • de facto standard• developed at Xerox, then IBM• extends Eclipse compiler• integrated with Eclipse IDE

abc:• research compiler• extensible for experiments in language design• aggressive optimisation• no IDE integration

The AspectBench Compiler

.class .java

bytecode

AspectJ

AST

parsing, type-checking

separator

advice weaving + postprocessing

Jimple IR

code generation + static weaving

Java

AST

Aspect

Info

Pol

yglo

t-ba

sed

fron

tend

Soo

t-ba

sed

back

end

Close-up of the advice weaverJimple IR

for bytecodeIR

for pointcuts

Shadowfinder Shadows Matcher Weaving

instructionsOptimiser

Analysisresults

Weaver

Woven Jimple

Analyser

Bytecodegenerator

Jimple is a typed, stackless3-address intermediate representationof Java bytecode

Does this work? cflow benchmarks (1)

figure quicksort sablecc ants LoD-sim LoD-weka Cona-stack Cona-sim0

1000

2000

3000

4000

5000

6000

abc-none

abc-intra

abc-inter

ajc 1.2

ajc 1.2.1

cflow benchmarks (2)

figure quicksort sablecc ants LoD-sim LoD-weka Cona-stack Cona-sim0

50

100

150

200

250

abc-intra

abc-inter

ajc 1.2.1

Sample language extension

Tracematches:

match regular patterns

on sequences of begin/end events

Failsafe enumeration over vectorspublic aspect FailSafeEnum {

pointcut vector_update() : call(* Vector.add*(..)) || … ;

tracematch(Vector ds, Enumeration e) {

sym create_enum after returning(e) : call(Enumeration+.new(..)) && args(ds);

sym call_next before : call(Object Enumeration.nextElement()) && target(e);

sym update_source after : vector_update() && target(ds);

create_enum call_next* update_source+ call_next

{ throw new ConcurrentModificationException(); }

}}

Database connection pooling

public aspect DBConnectionPoolingTM { …Connection tracematch(Connection connection, String url, String uid, String password) { sym get_connection1 after returning(connection) :

connectionCreation(url, uid, password); sym get_connection2 around (url, uid, password):

connectionCreation(url, uid, password); sym release_connection before:

connectionRelease(connection); get_connection1 release_connection get_connection2 { return connection; } }

void around() : connectionRelease(*) { }}

Anatomy of an abc extension

abc.tmglue for new, extended compiler

ast17 new AST node classesnew AST node factory

parsenew lexer and parser rules

visitone new pass to translate tracematches to advice

weavingaspectInfo

IR for tracematches (3 classes)matching

compile-time state machines (5 classes)weaver

Jimple code generation (4 classes)

No change w

hatsoever to abc base code

Performance of generated code

Memory usageof animations inJHotDraw +FailSafeEnum:NO leaks!

Running time of dbpooling: (seconds)Pure Java without pooling: 6.0with hand-coded pooling aspect: 1.0with tracematch 1.2

Sample of other abc extensions Bruno Harbulot:

LoopsAJloop joinpoints for parallelisation

Aotani & Masuhara:SCoPEstatic evaluation of conditional pointcuts

Bodden & Stolz:J-LOrun-time checking of LTL properties

abc goes shopping at GPCE

What typical GPCE technologies might be used in a tool like abc?

Frontend shopping list

Automated pass orderingdemand-driven attribute evaluation

Extending AST nodes in middle of hierarchyvirtual classes; nested inheritance

Rewrite rules and strategies

In the m

arket fo

r:

JastA

dd (Hedin and E

kman)

Stratego (V

isser e

t al)

Backend shopping list

Quotation for Jimple

Guarantees that generated Jimple iswell-formed

In the market for:

MetaBorg (Bravenboer a

nd Visser)

Safegen (Huang et al)

AspectJ design shopping list

Virtual classes in lieu of intertype declarations Regular query language (Datalog?) for

traces and static structure Hiding (and exposure) of implementation detail to

various degrees of “pure” advice(TR abc-2005-2)

Interaction of all this with generics

In th

e m

arke

t for

:

sem

antic

s!

Further information:http://aspectbench.org

Papers, dissertations, talksDownloadsBug reportsMailing lists

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Oxford University Computing Laboratory

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types for reflection, termination analysis, compositional model checking of higher-order programs, games semantics for aspects

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