A Model for Software Plans

Transcription

1 A Model for Software Plans Robert R. Painter and David Coppit Department of Computer Science The College of William and Mary

2 private static Vector readdata() { BufferedReader stdin = new BufferedReader( new InputStreamReader( System.in ) ); Vector list = new Vector(); int inputsize = Integer.parseInt( stdin.readline()); for (int i = 0; i < inputsize; i++) { int value = Integer.parseInt( stdin.readline()); list.add(new Integer(value)); Input return list; 2

3 private static Vector readdata() { BufferedReader stdin = new BufferedReader( new InputStreamReader( System.in ) ); Vector list = new Vector(); System.out.print( "Enter the number of values: " ); int inputsize = Integer.parseInt( stdin.readline()); System.out.println( "Enter " + inputsize + " values." ); for (int i = 0; i < inputsize; i++) { int value = Integer.parseInt( stdin.readline()); list.add(new Integer(value)); Input Prompting return list; 3

4 private static Vector readdata() { BufferedReader stdin = new BufferedReader( new InputStreamReader( System.in ) ); Vector list = new Vector(); System.out.print( "Enter the number of values: " ); int inputsize = 0; try { inputsize = Integer.parseInt( stdin.readline() ); catch (IOException e) { System.err.println( "Encountered an I/O exception. Exiting."); System.exit(1); System.out.println( "Enter " + inputsize + " values." ); for (int i = 0; i < inputsize; i++) { int value = 0; try { value = Integer.parseInt( stdin.readline() ); catch (IOException e) { System.err.println( "Encountered an I/O exception. Exiting."); System.exit(1); list.add(new Integer(value)); return list; Input Prompting I/O Exception 4

5 private static Vector readdata() { BufferedReader stdin = new BufferedReader( new InputStreamReader( System.in ) ); Vector list = new Vector(); System.out.print( "Enter the number of values: " ); int inputsize = 0; { boolean inputisvalid = false; while (!inputisvalid) { try { inputsize = Integer.parseInt( stdin.readline() ); catch (NumberFormatException e) { System.err.println( "Invalid number entered. (" + e.getmessage() + ")" ); catch (IOException e) { System.err.println( "Encountered an I/O exception. Exiting."); System.exit(1); System.out.println( "Enter " + inputsize + " values." ); for (int i = 0; i < inputsize; i++) { int value = 0; { boolean inputisvalid = false; while (!inputisvalid) { try { value = Integer.parseInt( stdin.readline() ); catch (NumberFormatException e) { System.err.println( "Invalid number entered. (" + e.getmessage() + ")" ); catch (IOException e) { System.err.println( "Encountered an I/O exception. Exiting."); System.exit(1); list.add(new Integer(value)); return list; Input Prompting I/O Exception Input Validation 5

6 Character Level Tangling Invasive compositions [Carver & Griswold 1999] fprintf(stderr, %s: failed to open %s\n, argv[0], szfilename); 6

7 Software Plans An approach for fine-grained separation and tangling of context-dependent concerns Inspired by architectural plans Multiple semi-independent code views Orthogonal to modular decomposition Each view has code for one or a few related concerns, in their necessary context A plan can reconcile concern code from other plans 7

8 8

9 Example: Plans for Tangling in GNU Sort if (fp == stdin) { /* Allow reading stdin from tty more than once. */ if (feof (fp)) clearerr (fp); static else void if (fp xfclose == stdout) (FILE *fp) { { if (fflush (fp)!= 0) { error (0, errno, _("flushing stdout")); cleanup (); else { exit (SORT_FAILURE); if (fclose (fp)!= 0) { error (0, errno, _("closing file")); static cleanup void xfclose (); (FILE *fp) { exit (SORT_FAILURE); /* Allow reading stdin from tty more than once. */ if (feof (fp)) if (fflush (fp)!= 0) { error (0, errno, _("flushing stdout")); cleanup (); clearerr (fp); exit (SORT_FAILURE); if (fclose (fp)!= 0) { error (0, errno, _("closing file")); cleanup (); exit (SORT_FAILURE); 9

10 Implementation One approach: use existing code model, augmented with concern information Annotate code with concerns Hide portions to create a plan Doesn't work: Forces ordering of unrelated code blocks Cost of manual concern annotation Edits to shared code may damage other plans Doesn't track edits by plan Not plan-oriented 10

11 Blocks if (fp == stdin) { /* Allow reading stdin from tty more than once. */ if (feof (fp)) clearerr (fp); else if (fp == stdout) { if ( fflush (fp)!= 0) { error (0, errno, _("flushing stdout")); cleanup (); exit (SORT_FAILURE); else { if ( fclose (fp)!= 0) { error (0, errno, _("closing file")); cleanup (); exit (SORT_FAILURE); Block: Span of text Set of related concerns Creation time 11

12 Plans if /* ( Allow fflush reading (fp)!= stdin 0) { from tty more than once. */ if error (feof(0, (fp)) errno, _("flushing stdout")); clearerr cleanup (); (fp); exit (SORT_FAILURE); Plan: Sequence of blocks (possibly repeated) Set of related concerns Set of context concerns Last update time 12

13 Document and View Document: Set of plans View: Concatenation of block spans Related code shown along with context code 13

14 Editing Operations Design principles: Reduce manually concern annotation No non-local editing effects Favor normal editing techniques Character-level concern manipulation Edits on a view modify the underlying document Transparently Maintain concern-code relationships New code automatically associated with related concerns (not context concerns) 14

15 Operations View ComputeView InsertSpan DeleteSpan Plan AddBlock DeleteBlock SplitBlock MergeBlock Document AddBlockToPlan DeleteBlockFromPlan SplitBlock MergeBlock UpdatePlan NewPlan Clipboard ImportBlocks ExportBlocks 15

16 Editing Example: New Plan if (feof (fp)) clearerr (fp); if ( fflush (fp)!= 0) { error (0, errno, _("flushing stdout")); cleanup (); exit (SORT_FAILURE); if ( fclose (fp)!= 0) { error (0, errno, _("closing file")); cleanup (); exit (SORT_FAILURE); Related: STDIN File fflush (fp) STDOUT Close Close Reconciliation Context: if (feof (fp)) clearerr (fp); fclose (fp) 16

17 Editing Example: Insert Span if (feof (fp)) clearerr (fp); if ( fflush (fp)!= 0) { error (0, errno, _("flushing stdout")); cleanup (); exit (SORT_FAILURE); if (fp == stdin) { if (feof (fp)) clearerr (fp); else if (fp == stdout) { fflush (fp) else { ; if ( fclose (fp)!= 0) { error (0, errno, _("closing file")); cleanup (); exit (SORT_FAILURE); fclose (fp) ; 17

18 Editing Example: Delete Span if (feof (fp)) clearerr (fp); if ( fflush (fp)!= 0) { error (0, errno, _("flushing stdout")); cleanup (); exit (SORT_FAILURE); if (fp == stdin) { if (feof (fp)) clearerr (fp); else if (fp == stdout) { fflush (fp) else { ; if ( fclose (fp)!= 0) { error (0, errno, _("closing file")); cleanup (); exit (SORT_FAILURE); fclose (fp) ; 18

19 Related Work Aspect-oriented programming [Kiczales] Better for loosely coupled, scattered concerns Hyperspaces [Tarr and Ossher] Interface-level SoC Code elision Folding: Hiding based on syntax (e.g. brackets) Hiding: P-Edit [Kruskal], Spotlight [Cox & Coppit] hide concern-annotated code Perspectives [Black and Jones], slicing [Weiser] and partial evaluation [Jones] Reduced views, but not independently editable 19

20 Current Status and Future Work Prototype proof-of-concept implements model Tool assisted, semi-automatic plan merging Language-dependent block dependency analysis Improved editing operations Inter-plan constraints Plan design Reverse-engineering of plans User studies, industrial studies Eclipse plugin 20

21 Conclusion Tangling of character-level concerns a problem Loosely-coupled tangling can be separated Context dependencies are important Software plans offer a potential solution Our model is a more sophisticated code representation That explicitly represents concerns and plans Supports software plans 21

22 Thank you Research Software Plans 22

23 Aspect-Oriented Programming Extend the language to allow cross-cutting concerns to be modularized [Kiczales, Tarr, Murphy, Griswold, ] Aspect abstraction encapsulates scattered code Compiler weaves aspects into classes Joinpoints: well-defined locations in the program (field access, method call, etc.) Pointcuts: declarative selection of joinpoints Advice: code to insert 23

24 Example: Prompting in AspectJ aspect Prompting { pointcut numberprompt(): execution(* Average.promptForNumber(..)); before(): numberprompt() { System.out.print( "Enter the number of values: " ); pointcut valueprompt(int inputsize): call(* Average.promptForValues(..)) && args(..,inputsize); before(int inputsize): valueprompt(inputsize) { System.out.println( "Enter " + inputsize + " values." ); 24

25 Example: I/O Exception Handling aspect IOExceptionHandling { declare soft : IOException : call(* *.*(..) throws IOException) && within(average); after() throwing(org.aspectj.lang.softexception ex) : execution(* Average.*(..)) && within(average) { System.err.println( "Encountered an I/O exception. Exiting."); System.exit(1); 25

26 private static int promptfornumber(final BufferedReader stdin) { int inputsize = 0; boolean inputisvalid = false; while (!inputisvalid) { try { inputsize = Integer.parseInt( stdin.readline() ); catch (NumberFormatException e) { System.err.println( "Invalid number entered. (" + e.getmessage() + ")" ); return inputsize; private static Vector promptforvalues(final BufferedReader stdin, final int inputsize) { Vector list = new Vector(); for (int i = 0; i < inputsize; i++) { int value = 0; boolean inputisvalid = false; while (!inputisvalid) { try { value = Integer.parseInt( stdin.readline() ); catch (NumberFormatException e) { System.err.println( "Invalid number entered. (" + e.getmessage() + ")" ); list.add(new Integer(value)); return list; private static Vector readdata() { BufferedReader stdin = new BufferedReader( new InputStreamReader( System.in ) ); int inputsize = promptfornumber(stdin); return promptforvalues(stdin, inputsize); 26

27 AOP Good For Scattering Pointcuts very general Method call/return Within some class Get/set of a field Exception handling Within call stack (cflow) Aspects meant to be context-independent Can hack context-dependent aspects by introducing dummy methods or refactoring to create needed join points 27

28 AOP Not Good For Tangling Invasive compositions [Carver & Griswold 1999] fprintf(stderr, %s: failed to open %s\n, argv[0], szfilename); AspectJ pointcuts poor for exposing and separating some concerns [Murphy et. al 2001] int[] match(... ) { // Multiline matching if (newline && (mymatch.offset > 0) && (input.charat(idx - 1) == \n )) return next(input,idx,eflags,mymatch); // Not BOL match if ((eflags & RE.REG_NOTBOL) > 0) return null;... 28