abc : the AspectBench Compiler for AspectJ

1. abc :the AspectBench Compilerfor AspectJ Oege de Moor Programming Tools Group University 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)

2. What is AspectJ? Disciplined Metaprogramming

3. Bluffer’s guide to aspect-lingo Static: 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

4. Events, joinpoints and advice 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(); Program: int x; void f() { x = x+1; } execute: … 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)

5. Example aspects AspectJ: extension of Java

6. No allocations with “new” in inner loop aspect 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); } }

7. 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; } }

8. Observing an oblivious subject aspect 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(); } } }

9. AOP languages: summary Conceptual model: traces of (composite) events at runtime Pointcuts: query language for events Advice: run extra code before/after/around selected events

10. Compiling AspectJ Match events at compile timewhenever possible: “weaving”

11. 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

12. The AspectBench Compiler .class .java parsing, type-checking AspectJ AST Polyglot-based frontend separator Aspect Info Java AST code generation + static weaving Soot-based backend Jimple IR advice weaving + postprocessing bytecode

13. Close-up of the advice weaver Jimple IR for bytecode IRfor pointcuts Shadow finder Shadows Matcher Weavinginstructions Optimiser Weaver Analysisresults Woven Jimple Analyser Jimple is a typed, stackless 3-address intermediate representation of Java bytecode Bytecode generator

14. Does this work? cflow benchmarks (1)

15. cflow benchmarks (2)

16. Sample language extension Tracematches: match regular patterns on sequences of begin/end events

17. Failsafe enumeration over vectors public aspect FailSafeEnum { pointcut vector_update() : call(* Vector.add*(..)) || … ; tracematch(Vector ds, Enumeration e) { sym create_enum afterreturning(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(); } } }

18. 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(*) { } }

19. Anatomy of an abc extension abc.tm glue for new, extended compiler ast 17 new AST node classes new AST node factory parse new lexer and parser rules visit one new pass to translate tracematches to advice weaving aspectInfo IR for tracematches (3 classes) matching compile-time state machines (5 classes) weaver Jimple code generation (4 classes) No change whatsoever to abc base code

20. Performance of generated code Memory usage of animations in JHotDraw + FailSafeEnum: NO leaks! Running time of dbpooling: (seconds) Pure Java without pooling: 6.0 with hand-coded pooling aspect: 1.0 with tracematch 1.2

21. 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

22. abc goes shopping at GPCE What typical GPCE technologies might be used in a tool like abc?

23. Frontend shopping list • Automated pass ordering demand-driven attribute evaluation • Extending AST nodes in middle of hierarchy virtual classes; nested inheritance • Rewrite rules and strategies In the market for: JastAdd (Hedin and Ekman) Stratego (Visser et al)

24. Backend shopping list • Quotation for Jimple • Guarantees that generated Jimple iswell-formed In the market for: MetaBorg (Bravenboer and Visser) Safegen (Huang et al)

25. 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 the market for: semantics!

26. Further information:http://aspectbench.org Papers, dissertations, talks Downloads Bug reports Mailing lists

27. Oxford Centre for Metacomputation Oxford University Computing Laboratory A new EPSRC-funded venture led by: Samson Abramsky, Tom Melham, Oege de Moor, and Luke Ong types for reflection, termination analysis, compositional model checking of higher-order programs, games semantics for aspects 4-year postdoc position available further postdocs for a shorter period ask Oege for further information