IBM Haifa Research Lab © 2008 IBM Corporation Automating Big Refactorings for Componentization and...

IBM Haifa Research Lab

© 2008 IBM Corporation

Automating Big Refactorings forComponentization and the Move to SOAIBM Programming Languages and Development Environments Seminar 2008

Aharon Abadi, Ran Ettinger and Yishai Feldman

Software Asset Management GroupIBM Haifa Research Lab


© 2008 IBM Corporation2

Background

What is Refactoring?

– The process of gradually improving the design of an existing software system by performing source code transformations that improve its quality in such a way that it becomes easier to maintain the system and reuse parts of it, while preserving the behavior of the original system

For example: Extract Method

void printOwing(double amount) {

printBanner();

// print details

print(“name:” + _name);

print(“amount:” + amount);

}

void printOwing(double amount) {

printBanner();

printDetails(amount);

}

void printDetails(double amount) {

print(“name:” + _name);

print(“amount:” + amount);

}Source: Martin Fowler’s online refactoring catalog



Prior Art

Refactoring to Design Patterns

+



Our Interest: Big Refactorings

Enterprise Architecture Patterns



The Gap: Techniques and Tools for Enterprise Refactoring

? ?



Automating Big RefactoringsEnterprise Refactorings

Separate Presentation Code from Business Logic (introduce the MVC pattern),

Extract Reusable Services (implementing SOA), etc.

Small RefactoringsRename Paragraph, Split/Merge Paragraphs, Extract/Inline Paragraph/Section/Program,

Extract Slice, Swap Consecutive (Independent) Statements/Sentences/Paragraphs/Sections,Split/Merge (Consecutive) Conditionals, Loop-Invariant Code Motion, etc.

Composition

Flexibility

Allow (user-determined)

choice between alternatives

Reliability*

Guarantee behavior preservation

Applicability

Avoid unnecessary rejections by precise

identification of (weak) preconditions

Deep Program AnalysisProgram analysis infrastructure for legacy enterprise software systems:

A powerful static analysis infrastructure using the plan-calculus intermediate representation

Enabling Technology

Required Quality

*See http://progtools.comlab.ox.ac.uk/projects/refactoring/bugreports for examples of bugs in modern IDEs



Example: Introduce the MVC Pattern



As-Is Version: Photo Album Web Application

Source: Alex Chaffee, draft “Refactoring to MVC” online article, 2002



To-Be Version: Photo Album Web Application

Source: Alex Chaffee, draft “Refactoring to MVC” online article, 2002

ControllerView

Model

Presentation Model



Small Refactorings on the move to MVC

All kinds of renaming

– Variables, fields, methods, etc.

Extracting program entities

– Constants, local (temp) variables, parameters, methods (Extract Method, Replace Temp with Query, Decompose Conditional), classes (Extract Class, Extract Superclass, Extract Method Object)

– Some reverse refactorings too, to inline program entities

Moving program entities

– Constants, fields, methods (Move Method, Pull-Up Method), statements (Swap Statements), classes

Replace Algorithm



Shortcomings of Eclipse on the move to MVC

Missing implementation for key transformations

– Extract Class, Extract Method Object

Buggy implementation of some refactorings

– Extract/Inline Local Variable: Ignores potential modification of parameters (on any path from source to target location)

– See http://progtools.comlab.ox.ac.uk/projects/refactoring/bugreports for examples of bugs in (earlier releases of) modern IDEs

Restricted implementation of existing refactorings

– Extract Method: contiguous code only; weak control over parameters

– Move Method: Source class must have a field with type of target class

– Extract Local Variable: No control over location of declaration



Thanks!



Backup



Internal Representation: The Plan Calculus

Wide-spectrum

– Specification to implementation

Canonical

– Abstracts away from syntactic variations

Language independent

– All legacy languages have similar capabilities

Expressive

– Directly expresses program semantics in terms of data-flow and control-flow

Convenient for machine manipulation

– Naturally expresses semantic transformations

Rich, C. 1986. A formal representation for plans in the programmer's apprentice. In Readings in Artificial intelligence and Software Engineering, C. Rich and R. C. Waters, Eds. Morgan Kaufmann Publishers, San Francisco, CA, 491-506 .



MOVE 0 TO TOTAL-SALE

MOVE 0 TO TOTAL-PAY

PERFORM VARYING i FROM 1 BY 1 UNTIL i > DAYS

ADD SALE(i) TO TOTAL-SALE

COMPUTE TOTAL-PAY = TOTAL-PAY + 0.1*SALE(i)

IF SALE(i)>1000

ADD 50 TO TOTAL-PAY

END-IF

END-PERFORM

COMPUTE PAY = TOTAL-PAY / DAYS + 100

COMPUTE PROFIT = 0.9*TOTAL-SALE - COST

MOVE 0 TO TOTAL-PAY



IF SALE(i)>1000

ADD 50 TO TOTAL-PAY

END-IF

END-PERFORM





END-PERFORM



MOVE 0 TO TOTAL-PAY




IF SALE(i)>1000

ADD 50 TO TOTAL-PAY

END-IF

END-PERFORM



Program Sliding A family of provably-correct code-motion

untangling transformations

– Automate slice extraction: Sequential composition of a selected slice with its complement (i.e. co-slice); Useful for refactoring, componentization, the move to SOA, obfuscation, etc.

– Combine statement reordering with code duplication, including duplication of assignments

– Benefit from the best of leading earlier solutions without suffering some of their respective deficiencies

Sliding is particularly strong in

– Preserving behavior

– Maximizing reuse (of extracted computation’s results, in the complement)

– Minimizing code duplication, i.e. yielding a smaller, more desirable complement;

– Improving applicability, i.e. less reasons to reject a request

Example source: Lakhotia and Deprez (rewritten in COBOL)



Towards a COBOL Refactoring Catalog Rename Paragraph

– This refactoring might look trivial, but as it is with the renaming of variables, it must be done with care: the new name must be valid, it must not conflict with existing names, and it must be replaced correctly in each call (PERFORM, GO TO, etc.), without violating any column restrictions

Split/Merge Paragraphs– When merging two consecutive paragraphs, one must check the second is not referenced, or if it is, its reference must

always follow a call to the first paragraph such that the two calls can be merged. Similarly, one must verify that any call to the first paragraph is either followed by a call to the second, or it must be a non-returning call that implies fall-through to the second paragraph

Extract/Inline Paragraph/Section/Program– Could support clone detection too, such that upon extraction, the tool will identify (at least exact) clones of the selected

code, and suggest to replace it too with a call to the newly introduced program Extract Slice (through Sliding)

– First support the extraction of the code for computing a set of variables in a selected compound statement (or sentence); later add support for extraction from internal program points, i.e., the slicing criteria involves pairs of program point and (sets of) variables of interest (at that particular point); and finally support arbitrary method extraction, i.e., the slicing criteria involves a set of statements (or sentences), not necessarily contiguous, for extraction

Swap Consecutive (Independent) Executable Program Entities– Such as compound statements, sentences, and even paragraphs or sections

Split/Merge (Consecutive) Conditionals– So long as two instances of the conditional’s predicate are guaranteed to evaluate similarly

Loop-Invariant Code Motion– Computation flavor: A loop-invariant computation is moved inside/outside that loop, as in optimizing compilers– Conditional flavor: Instead of a computation, it is a loop-invariant conditional being moved

• If moved out, the loop itself is duplicated, for each branch of the conditional, but with each branch simplified based on the known conditional’s result

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