IOA PRESENTATION

1. IOAPRESENTATION May 01, 1999

2. IOA2JAVA Tool Joe Balthazar Jim Byrne Christine Kenney Ainsley Nathaniel Computer Science & Engineering Department The University of Connecticut 191 Auditorium Road, Box U-155 Storrs, CT 06269-3155

3. Input/Output Automata P1 P2 init(v2) init(v1) decide(v2) Process decide(v1) send(m(1,2)) Channel C(1,2) receive(m(2,1)) receive(m(1,2)) C(2,1) send(m(2,1))

4. Structure of an IOA • Main components of an I/O Automaton(A): • sig(A), a signature • states(A), a set of states • start states • trans(A), a state-transition relation that follows a precondition-effect style • input actions - no preconditions and hence, are permanently enabled • internal and output actions - have preconditions and effects • optional tasks

5. Objectives • Create a tool to convert the general structure of an IOA to Java code • IOA can be used for algorithm correctness proofs • Recognize only a subset of the language • Automaton name, states and data types • Input, internal, and output actions • Preconditions and effects • Parses majority of language • Convert a single IOA to a single Java class • Produce necessary additional Java code to create a executable program with IOA functionality • Code will run on one machine

6. Assumptions • Action names, parameters, and state variables are unique • Deal only basic data types • boolean • double • int • Preconditions and effects written as Java Code • May change state variables so long as same names are used • Code copied directly to Java class

7. Assumptions • Internal and output actions have no parameters • Parameters values selected by IOA code in preconditions based on state • A large enough subset of IOA is not yet implemented to do this • Changes to IOA code in parser • All keywords have the first letter capitalized ie. Automaton, Transition, etc. • Some symbols were changed to accommodate the keyboard ie. E - There exist. • Java types were used instead of IOA types- this eliminated the need for a symbol table. • Type checking done by the Java Compiler.

8. Java Compiler Compiler • Compiler Tool for Java Language. • The Java equivalent of Lex and Yacc • Parses grammar to produce Java code • JavaCC uses an input file written in a standard BNF grammar. • Example of simple BNF grammar • <exp> :: = <simp exp><rel op> <simp exp> • <rel op> :: = < | >= | <= | = | >

9. Compiler Procedure • Get the tokens • The first part of the JCC specification defines the tokens for the language. • Parse the Language • The second part defines the transitions that make up the language. • Generate the code • The compiler output is generated by the insertion of Java code in the transitions.

10. IOA Tokens • IOA Token definitions. • < AUTOMATON: “Automaton” > • < TRANSITION: “Transition” > • < INPUT: “Input” > • < OUTPUT: “Output” > • Resulting Java code is too complicated to put here, looks like assembly language.

11. IOA grammar to JavaCC grammar • IOA grammar specification translates directly into JCC grammar because of similarity in structures. • states ::= ‘states’ state,+ (‘so’ ‘that’ predicate)? • void states() : • {} • { • <STATES> state()(“,” state())* • (<SO> <THAT> predicate())? • }

12. Translation of Grammar Cont’d • JavaCC grammar with Java code inserted to create the IOA compiler. • states ::= ‘states’ state,+ (‘so’ ‘that’ predicate)? • void states() : • {} • { {String lTokStr;} • <STATES> lTokStr = state() • {pwOutput.println(lTokStr);} • ("," lTokStr = state() • {pwOutput.println(lTokStr);})* • ( <SO> <THAT> predicate())? • }

13. Java file which implements the Parser • The IOA compiler takes an automaton definition as input and produces an equivalent automaton, written in Java, as output. • static final public void states() throws ParseException { • String lTokStr; • jj_consume_token(STATES); • lTokStr = state(); • System.out.println(lTokStr); • label_12: • while (true) { • if (jj_2_38(2)) { ;

14. Differences in Grammars • JCC does not permit left recursion and hence two transitions have to be modified. • For example, A  C | AB is a transition with left-recursion. • The equivalent transition A  CB+ does not contain left recursion and can be used in a JavaCC grammar file. • subterm ::= subterm (opSym subterm)+ • | (quantifier | opSym)* opSym secondary • | (quantifier | opSym)* quantifier primary • | secondary opSym*

15. Left Recursion Removed • String subterms() : • { } • { • subterm() (opSym() subterm())* • } • String subterm() : • { } • { • ( ((quantifier() | opSym())* secondary()) • | ((quantifier() | opSym())* quantifier() primary()) • | ( secondary() (opSym())*) • ) • }

16. The FibonacciSkew IOA • What does it do? • Produces the Fibonacci sequence • The sequence can be skewed by a certain value from time to time • States • ready indicate state of sequence generation • skew value • printFlag indicates print state • first, second, current holding last three sequence values

17. The FibonacciSkew IOA • Actions in the IOA • Input action to start or end the sequence • Input action to skew the sequence • Internal action that calculates the next value in the sequence • Output action that prints the next value

18. The FibonacciSkew IOA setReady print FibonacciSkew skew Input Action Output Action calculate Internal Action

19. IOA States to Private Data • IOA States automaton FibonacciSkew states ready: boolean := false; skew: int := 0; printFlag: boolean := false; first: int := 1; sec: int := 0; current: int := 0; • Private Data in Java Class class FibonacciSkew { // Private Data private boolean ready = false; private int skew = 0; private boolean printFlag = false; private int first = 1; private int sec = 0; private int current = 0; // Public Methods };

20. Input Action to Public Method • IOA Input Action input setReady(flag: boolean) eff $ if (ready!=flag) { ready = flag; first = 1; sec = 0; current = 0; } $ • Public Method in Java Class public void setReady(boolean flag) { if (ready!=flag) { ready = flag; first = 1; sec = 0; current = 0; } }

21. Input Action to Public Method • IOA Input Action input skew(k: int) eff $ if (ready==true) skew = k; else System.out.println(“Cannot skew: No sequence is being generated”); $ • Public Method in Java Class public void skew(int k) { if (ready==true) skew = k; else System.out.println(“Cannot skew: No sequence is being generated”); }

22. Internal and Ouput Actions to Public Methods • IOA Internal Action internal calculate() pre $ return (ready); $ eff $ current = first + second + skew; skew = 0; first = sec; sec = current; printFlag = true; $ • Public Methods in Java Class public boolean Precalculate() { return (ready); } public void calculate() { current = first + second + skew; ... }

23. Internal and Ouput Actions to Public Methods • IOA Output Action output print() pre $ return (printFlag); $ eff $ System.out.println(“The current value in sequence is “ + current); printFlag = false; $ • Public Methods in Java Class public boolean Preprint() { return (printFlag); } public void print() { System.out.println(“The current value in sequence is “ + current); printFlag = false; }

24. IOA Input Parameters • paramFibonacciSkew.java • Created by Parameter.java • Simulates input parameter values for input actions coming in from environment • IOA Input Action parameter input setReady(flag: boolean) • Public Java method for each parameter public boolean returnflag() { input = getInput(“flag”); return retboolean(input); }

25. Helper Methods • Methods for converting String to type value private boolean retboolean(String s) { return Boolean.valueOf(s).booleanValue(); } • Method to get any parameter value from user public String getInput(String message) { String response = “”; System.out.println(“Enter “ + message); try { BufferedReader brInp.readLine(); response = brInp.readLine(); } catch(Exception e){ e.printStackTrace(); } return response; }

26. IOA Scheduler • FibonacciSkewScheduler.java • Created by Scheduler.java • Contains main program which calls a round robin scheduler to cycle through actions public static void RoundRobin() { boolean NotQuit; FibonacciSkew ioaFibonacciSkew = new FibonacciSkew(); paramFibonacciSkew inputFibonacciSkew = new paramFibonacciSkew(); while(NotQuit) { // Check each action NotQuit = askuser(“cycle again”); } }

27. Round Robin Scheduler Internal Output Input while(NotQuit) { if(askuser(“setReady”)) { ioaFibonacciSkew.setReady( inputFibonacciSkew.Returnflag()); } if(askuser(“skew”)) { ioaFibonacciSkew.skew( inputFibonacciSkew.Returnk()); } if(ioaFibonacciSkew.PreCalculate()) { ioaFibonacciSkew.calculate(); } if(ioaFibonacciSkew.Preprint()) { ioaFibonacciSkew.print(); } NotQuit = askuser(“cycle again”); }

28. Future Research • Solving Composition of Automata • Public Composed IOA Class Approach • All classes are in a package • Each independent IOA class is private • The composed IOA class is public • IOA Class Library Approach • All IOAs have their own class in a library • Create a new composed IOA importing 2 or more IOA classes from the library • Put back composed classes in library and reuse • Combination of Both • Package last composition of classes from library • Adapt parser to handle assumes clause

29. Future Research • Generation of pre-conditions and effects in Java • Determining parameters for internal and output actions • Common mechanism for selecting values from state • Consider distributed systems modeled by IOA • Interaction in Java • Use of Java distributed technologies

30. References • MIT-Theory of Distributed Systems Group • I/O Automata Model, Language and Tool Set. http://theory.lcs.mit.edu/tds/~vaziri/ioa.html • S. J. Garland, N. A. Lynch, and M.Vaziri, “IOA: A Language for Specifying, Programming, and Validating Distributed Systems Draft”, December 1997. • O. M. Cheiner and A. A. Shvartsman, “Implementing An Eventually-Serializable Data Service as a Distributed System Building Block”, July 1998. • Java Compiler Compiler - The Java Parser Generator - http://www.suntest.com/JavaCC/

31. Flow ioaname.ioa IOA.java associated Java files IOA.jj grammar file *.class MethodInfo.java Scheduler.java Parameter.java Executable IOA ioaname.java ioanameScheduler.java paramioaname.java ioanameScheduler *.class javacc javac java java javac