ArchJava A software architecture tool –components –connections –constraints on how components interact Implementation must conform to architecture

References ECOOP 2002 paper ICSE 2002 paper website on ArchJava ArchJava reference manual

Architectural Conformance communication integrity –each component in the implemented system may only communicate directly with the components to which it is connected in the architecture.

public component class Parser { public port in { provides void setInfo(Token symbol, SymTabEntry e); requires Token nextToken() throws ScanException; } public port out { provides SymTabEntry getInfo(Token t); requires void compile (AST ast);} void parse (String file) { Token tok = in.nextToken(); AST ast = parseFile(tok); out.compile(ast); } AST parseFile(Token lookahead) { … } void setInfo(Token t, SymTabEntry e) {… } SymTabEntry getInfo(Token t) { … } … } strange that parse does not belong to a port; parse is provided.

collaboration Parser { public participant in { provides void setInfo(Token symbol, SymTabEntry e); requires Token nextToken() throws ScanException; } public participant out { provides SymTabEntry getInfo(Token t); requires void compile (AST ast); void parse (String file) { Token tok = in.nextToken(); AST ast = parseFile(tok); out.compile(ast); } AST parseFile(Token lookahead) { … } void setInfo(Token t, SymTabEntry e) {… } SymTabEntry getInfo(Token t) { … } … } can we do the same with an aspectual collaboration?

public component class Compiler { private final Scanner scanner = … ; private final Parser parser = … ; private final CodeGen codegen = … ; connect scanner.out, parser.in; connect parser.out, codegen.in public static void main(String args[]) { new Compiler().compile(args); } public void compile(String args[]) { // for each file in args do: … parser.parse(file); … }

Composite components sub component: component instance nested within another component. singleton sub components: final connections: connect primitive is symmetric –bind each required method to a provided method with same name and signature –args to connect: components own ports or those of subcomponents in final fields

Composite components Provided methods can be implemented by forwarding invocations to sub components or to the required methods of another port. Alternative connection semantics: write smart connectors. Only a component’s parent can invoke its methods directly.

Dynamic architectures create component instances with new. typed references to sub components may not escape the scope of their parent. Garbage collection when components are no longer reachable through references or connections.

public component class WebServer { private final Router r = new Router(); connect r.request, create; // may be instantiated at run-time // personality analogy connect pattern Router.workers, Worker.serve; public void run() { r.listen(); } private port create { provides r.workers requestWorkers() { final Worker newWorker = new Worker(); r.workers connection = connect(r.workers, newWorker.serve); return connection; }

public component class Router {

Limitations of ArchJava only Java inter-component connections must be implemented through method calls (not events, for example) focus on communication integrity no reasoning about temporal ordering of architectural events shared data

Example: Aphyds Developed by EE professor with PhD in CS

Hypotheses Do those hypotheses hold for aspectual collaborations? A port corresponds to a participant. In ArchJava: no renaming of methods in connectors

Hypotheses Refactoring an application to expose its architecture is done most efficiently in small increments Applications can be translated into ArchJava with a modest amount of effort and without excessive code bloat

Hypotheses Expressing software in ArchJava highlights refactoring opportunities by making communication protocols explicit. Note: the name of a port gives a clue about the purpose of the port’s methods.

Hypotheses Using separate ports and connections to distinguish different protocols and describing protocols with separate provided and required port interfaces may ease program understanding tasks. Communication integrity in ArchJava encourages local communication and helps to reduce coupling between components.

Architectural Refactoring during Translation ArchJava’s

Ideas Can ArchJava constraints be simulated in AspectJ? Simulate a component class with aspects that check the constraints? What are the connections between ports and participants? Law of Demeter and default architecture.

Ports and Participants Sounds like ports are a second very useful application of the participant idea. Participants are connected in a graph; ports don’t rely on that.

Ports and Participants ArchJava has provides/requires connect: link ports no renaming no component merging AC has provides/requires attach: link participants renaming of method names component merging

component class Flying { port flier { provides void fly(); requires void takeOff(); requires void land(); …}} component class Bat { port flier_infra { provides void takeOff(); provides void land(); … } } component class FlyingBat { private final Flying f = … ; private final Bat b = … ; connect f.flier, b.flier_infra; public void fly() { f.fly();} }

Topic Switch

Hygienic Components and Mixins class AddAttribute extends C{ // mixin class that adds a field of type // Attribute to any class C private Attribute _a; void setAttribute(Attribute a) {_a = a;} Attribute getAttribute() {return _a;} } class Point { … }