aharon abadi, ran ettinger and yishai feldman software asset management group
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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
IBM 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
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© 2008 IBM Corporation3
Prior Art
Refactoring to Design Patterns
+
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Our Interest: Big Refactorings
Enterprise Architecture Patterns
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The Gap: Techniques and Tools for Enterprise Refactoring
? ?
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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
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Example: Introduce the MVC Pattern
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As-Is Version: Photo Album Web Application
Source: Alex Chaffee, draft “Refactoring to MVC” online article, 2002
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© 2008 IBM Corporation9
To-Be Version: Photo Album Web Application
Source: Alex Chaffee, draft “Refactoring to MVC” online article, 2002
ControllerView
Model
Presentation Model
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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
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© 2008 IBM Corporation11
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
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© 2008 IBM Corporation12
Thanks!
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© 2008 IBM Corporation13
Backup
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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 .
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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
PERFORM VARYING i FROM 1 BY 1 UNTIL i > DAYS
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
MOVE 0 TO TOTAL-SALE
PERFORM VARYING i FROM 1 BY 1 UNTIL i > DAYS
ADD SALE(i) TO TOTAL-SALE
END-PERFORM
COMPUTE PROFIT = 0.9*TOTAL-SALE - COST
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
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)
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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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