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Automatic Workarounds: Exploiting the Intrinsic Redundancy of Software to Improve Reliability Antonio Carzaniga , Alessandra Gorla, Nicol` o Perino, Mauro Pezz` e Faculty of Informatics University of Lugano Switzerland March 22, 2012 Scope

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Automatic Workarounds: Exploiting the Intrinsic Redundancy

  • f Software

to Improve Reliability

Antonio Carzaniga, Alessandra Gorla, Nicol`

  • Perino, Mauro Pezz`

e

Faculty of Informatics University of Lugano Switzerland

March 22, 2012

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Scope of this work:

reliability = correctness reliability ≈ fault tolerance

“self-healing. . . ”

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reliability ⇒ redundancy

. . . some redundancy is necessary.

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Examples

N-version programming [Avizenis’75] Recovery blocks [Randell’75]

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Examples

N-version programming [Avizenis’75] Recovery blocks [Randell’75] Many forms of specifications

◮ invariants ◮ assertions ◮ pre/post-conditions

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Examples

N-version programming [Avizenis’75] Recovery blocks [Randell’75] Many forms of specifications

◮ invariants ◮ assertions ◮ pre/post-conditions

Data diversity [Ammann&Knight’88] Robust data structures [Taylor et al.’80] “Rejuvenation” [Garg et al.’96] Rx: “bugs as allergies” [Qin et al.’07] Micro-reboots [Candea et al.’03] . . .

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Examples

N-version programming [Avizenis’75] Recovery blocks [Randell’75] Many forms of specifications

◮ invariants ◮ assertions ◮ pre/post-conditions

Data diversity [Ammann&Knight’88] Robust data structures [Taylor et al.’80] “Rejuvenation” [Garg et al.’96] Rx: “bugs as allergies” [Qin et al.’07] Micro-reboots [Candea et al.’03] . . .

deliberate redundancy

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Examples

N-version programming [Avizenis’75] Recovery blocks [Randell’75] Many forms of specifications

◮ invariants ◮ assertions ◮ pre/post-conditions

Data diversity [Ammann&Knight’88] Robust data structures [Taylor et al.’80] “Rejuvenation” [Garg et al.’96] Rx: “bugs as allergies” [Qin et al.’07] Micro-reboots [Candea et al.’03] . . .

deliberate redundancy

expensive

and possibly ineffective!

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Hypothesis:

Software is intrinsically redundant

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Hypothesis:

Software is intrinsically redundant

. . . and this intrinsic redundancy can be used to deal with faults at runtime.

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Hypothesis:

Software is intrinsically redundant

. . . and this intrinsic redundancy can be used to deal with faults at runtime. at practically no cost

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Prior Plausibility

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Prior Plausibility

Code clones

◮ pervasive even in binaries [Sæbjørnsen et al.:ISSTA’09] ◮ including semantic clones that are syntactically different [Gabel et

al.:ICSE’08,Jiang&Zu:ISSTA’09]

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Prior Plausibility

Code clones

◮ pervasive even in binaries [Sæbjørnsen et al.:ISSTA’09] ◮ including semantic clones that are syntactically different [Gabel et

al.:ICSE’08,Jiang&Zu:ISSTA’09]

Design for reusability

◮ display functions in JQuery: fadeIn(), show(), fadeTo(), animate() ◮ mutually interchangeable methods in Java SWT: setLocation(Point)

and setLocation(int x, int y), setSize(Point) and setSize(int), etc.

◮ alternative operations in Java containers: add(Component comp),

add(Component comp, int index), add(Component comp, Object constraints), add(Component comp, Object constraints, int index), remove(Component comp), remove(int index), removeAll(), etc.

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Prior Plausibility (2)

Performance optimization

◮ in the Apache Ant library StringUtils.endsWith() reimplements

java.lang.String.endsWith(); CollectionUtils.frequency() reimplements java.util.Collection.frequency(), SelectorUtils.tokenizePathAsArray() reimplements tokenizePath(), etc.

◮ the GNU Standard C++ Library has two implementations of stable

sort (insertion-sort used for small sequences, and merge-sort for the general case)

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Prior Plausibility (2)

Performance optimization

◮ in the Apache Ant library StringUtils.endsWith() reimplements

java.lang.String.endsWith(); CollectionUtils.frequency() reimplements java.util.Collection.frequency(), SelectorUtils.tokenizePathAsArray() reimplements tokenizePath(), etc.

◮ the GNU Standard C++ Library has two implementations of stable

sort (insertion-sort used for small sequences, and merge-sort for the general case)

Backward compatibility

◮ 45 classes and 365 methods in the Java 6 standard library are

deprecated, and they duplicate exactly or almost exactly the functionality of newer classes and methods

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Example: Google Maps Issue n. 1305

polyline.enableDrawing();

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Example: Google Maps Issue n. 1305

v = polyline.deleteVertex(polyline.getVertexCount()-1); polyline.insertVertex(polyline.getVertexCount()-1,v); polyline.enableDrawing();

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Do Workarounds Exist?

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Do Workarounds Exist?

Analysis of issues recorded in issue-tracking systems system reported faults selected “workaround” confirmed workarounds

Google Maps ≈ 400 63 43 YouTube 21 9

10% of reported faults in Google Maps admit to a workaround

◮ conservative estimate

42% of reported faults in YouTube admit to a workaround

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Do Automatic Workarounds Exist?

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Do Automatic Workarounds Exist?

Which workarounds can be plausibly generated automatically? system confirmed workarounds confirmed automatic workarounds

Google Maps 43 14 YouTube 9 5

33% workarounds in Google Maps could be generated automatically 55% of workarounds in YouTube could be generated automatically

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space

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General Idea

application state space failure detection

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General Idea

application state space failure detection checkpoint recovery

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General Idea

application state space failure detection checkpoint recovery workaround

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Web Applications

An initial “easy” context. . .

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Web Applications

An initial “easy” context. . . failure detection: the user can do that for us

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Web Applications

An initial “easy” context. . . failure detection: the user can do that for us checkpoint/recovery: simply reload the page

◮ applications are mostly stateless (on the client-side)

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Web Applications

An initial “easy” context. . . failure detection: the user can do that for us checkpoint/recovery: simply reload the page

◮ applications are mostly stateless (on the client-side)

workarounds: alternative sequences

◮ represented as code-rewriting rules

Example: setTags($X,$Y); − → setTags($X); appendTags($Y);

◮ implemented as a proxy or as a browser extension ◮ priority scheme, automatic oracle, . . . [Carzaniga et al. FSE’10]

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Does It Work?

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Does It Work?

system rewriting rules issues considered known WA unknown WA total

Google Maps 39 14 24 38 YouTube 40 5 1 6 jQuery 68 25 77 102

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Does It Work?

system rewriting rules issues considered known WA unknown WA total

Google Maps 39 14/14 15+9/24 38 YouTube 40 5/5 1/1 6 jQuery 68 25/25 42+35/77 102 (found, not found)

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Does It Work?

system rewriting rules issues considered known WA unknown WA total

Google Maps 39 14/14 15+9/24 38 YouTube 40 5/5 1/1 6 jQuery 68 25/25 42+35/77 102 (found, not found) Google Maps: 76% YouTube: 100% jQuery: 65%

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Does It Work?

system rewriting rules issues considered known WA unknown WA total

Google Maps 39 14/14 15+9/24 38 YouTube 40 5/5 1/1 6 jQuery 68 25/25 42+35/77 102 (found, not found) Google Maps: 76% YouTube: 100% jQuery: 65% max iterations found not found 9 15 8 5 8

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Does It Work?

system rewriting rules issues considered known WA unknown WA total

Google Maps 39 14/14 15+9/24 38 YouTube 40 5/5 1/1 6 jQuery 68 25/25 42+35/77 102 (found, not found) Google Maps: 76% YouTube: 100% jQuery: 65% max iterations w/ oracle found not found 2 3 1 2 2

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Current and Future Work

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Current and Future Work

Supporting general-purpose applications Measuring software’s intrinsic redundancy Approximate redundancy: almost-equivalent sequences Dealing with multi-threaded applications. . .

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Anything to do with. . .

multiplicity computing?

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Anything to do with. . .

multiplicity computing?

Yes! Use available computing power to improve reliability by exploiting software’s intrinsic redundancy

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right now it’s only a notion but I think I can get money to make it into a concept and later turn it into an idea

[Woody Allen ’77, “Annie Hall”]

exploiting intrinsic redundancy by design extended contracts + infrastructure + runtime analysis

document potential intrinsic redundancy “orchestrate” some development at runtime