Method Shelters : Another Way to Resolve Class Extension Conflicts

Method Shelters :Another Way to Resolve ClassExtension ConflictsClassboxes でも Refinements でもない別のやり方 Shumpei Akai / 赤井駿平 @flexfrank

What I talk about todayOpen Class causes conflicts of methodsMethod Shelters resolve it!

% whoami Shumpei Akai / 赤井駿平 @flexfrank Ph.D. Student / 学生(博士課程) ◦ 東工大の千葉研 ◦ Programming Languages and Moduralization ◦ プログラミング言語とモジュール化 Today’s topic is my current research

Open Class Ruby’s one of the important features You can (re)define methods in existing classes ◦ including Object, Integer, Array, … Frequently used in Ruby world

in open-uri open-uri redefines “open” method ◦ It accepts URI open("http://penguindrum.jp/"){|f|f.read} # => Errno::ENOENT: No such file or directory require "open-uri” open("http://penguindrum.jp/"){|f|f.read} # => "<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1- transitional.dtd”…”

in Ruby on Rails ActiveSupport adds various convenient methods to core classes ◦ e.g. 10.megabytes # => 10485760 1.day.ago # => Sat Jul 16 16:15:00 +0900 2011 "survival strategy".pluralize #=> "survival strategies"

Or Monkey Patching

Problem of Open Class Methods may conflict When One library adds a method ◦ and another library adds a method with the same name in the same class The method defined first is vanished! ◦ depends on the order of “require” ◦ Confusing!

Method conflicts I encountered about five years ago ◦ Ruby on Rails and flvtool added a method to String ◦ they used String as binary/array of int Difficult to collaborate these two libraries ◦ I separated processes ◦ communicating via dRuby

Another example of conflicts “mathn” redefines the “Integer#/” ◦ returns a Rational object ◦ Ordinary code expects “/” returns a integer  Programs get broken

Existing Solutions Several module systems are proposed to resolve conflicts ◦ Selector namespaces (for Smalltalk) ◦ Classboxes (for Smalltalk and Java) ◦ Refinements (for Ruby) ◦ …

Refinements Proposed by Shugo Maeda [ruby-core:33322] class Foo module MathN using MathN refine Fixnum do def foo def /(other) p1/2 quo(other) end end end end end f = Foo.new f.foo #=> (1/2) p1/2

Refinements (cont.) Refinements changes behavior of methods in a lexical scope ◦ methods defined by Refinements are not enabled in indirectly called methods ◦ No local rebinding I need local rebinding ◦ e.g. scoped monkey patching

Classboxes You might have known via matz’s diary

Classboxes A classbox restrict the scope of methods A classbox can import a class in another classbox ◦ You can use an imported class ◦ You can add/redefine methods to the imported class ◦ A redefined method can be called from the imported class  Local rebinding property

Classboxes Cited from “Classbox/J: Controlling the Scope of Change in Java”

The Problem in Classboxes Importing overwrites internally used classes ◦ Importing causes another conflict

The Problem in Classboxes Redefines Original Integer#div IntegerUses redefined Use original Integer#div Integerreturns rational Oops! returns integer

I need another module system A new module should: ◦ have local rebinding ◦ provide a way to resolve conflicts cause by importing ◦ not depends on the order of load

Method Shelters

Key conceptHide your methodsHide your imports

What is a method shelter A method shelter is a module which provides a scope of methods ◦ define methods in a method shelter ◦ import other method shelters  You can call methods in the imported shelter  You can call methods in the shelter which is importing the current shelter  for local rebinding call importee call importer

A Code with Method Sheltersshelter :MathN do class Fixnum # fixed size integer in Ruby def /(x) Rational(self,x) end endendshelter :Average do class Array def avg sum = self.inject(0){|r,i|r+i} sum / self.size end end hide import :MathNend

What conforms a method shelter A method shelter is separated into tow parts ◦ An exposed chamber and a hidden chamber ◦ in order to protect internally used methods ◦ Each chamber can define methods and import - Exposed - Hidden

Exposed Chambers S0 - Obj#m0 for public API Exposed methods ◦ Visible from importer ◦ Importer can call or redefine exposed S1 methods Exposedly import ◦ Transitive importing ◦ Imported methods are S2 also visible from importer

Hidden chamber S0 - Obj#m1 - Obj#m0 for internally used methods Hidden method S1 ◦ invisible in importing shelter Hiddenly import S2 ◦ Imported methods are not exposed

Global Methods Ordinal methods not in shelters ◦ Callable from any shelter ◦ Global methods can call methods in a shelter if the caller is in the shelter Global - Obj#g0 S0 obj.g0()

No Ambiguity If 2+ methods are found in imported shelters S3 - C#m0 ◦ Error! S1 S2 - C#m0 S0 Error!

Syntax I don’t want to edit parse.y define methods in a block shelter :ShelterName do class Foo def hoge # <- defined in the method shelter end end end

Syntax: Importshelter :ShelterName do import :AnotherShelterNameend

Syntax: hide “hide” method switches a chamber ◦ do def or import below “hide”shelter :ShelterName do # exposed chamber hide # hidden chamberend

Evaluate Evaluate within a shelter shelter_eval :ShelterName do #shelter is enabled end

Method Lookup Algorithm 1. look up hidden-chamber 2. look up exposed-chamber 3. look up global methods If not found, go to superclass

8 3 7 6 2 5 1 startGlobal 9 4

Found! 1Start Global

Implementation Based on Ruby 1.9.2 Add one implicit argument to method: ◦ A node of method shelter tree

Optimization: Method Cache Shelter node cache ◦ Caches method entry in a node of shelter Extend inline cache ◦ Size of an inline cache : 3 word -> 4word (per method call) ◦ Stores the found shelter node

Performance: empty methods Call a empty method 10,000,000 times ◦ Less than 5% overhead when shelters are used

Performance: Fibonacci fib(33) in a method shelter ◦ Up to 20% overhead

Performance: Ruby on Rails Enabled in an action method ◦ Numeric#/.*bytes?/ methods are in a shelter In the action ◦ 1. Call one method in shelter ◦ 2. One access to SQLite via ActiveRecord on WEBRick Rails3

Performance: Ruby on Rails (result)  4% overhead on production env.  50% on development ◦ Method caches are invalidated per req.productiondevelopment

Cache hit ratio on rails Count shelter’s cache hit

Performance: tDiary 3.0.1 defined String#to_a, String#each, String#method_ missing in a shelter ◦ These are used for compatibility of 1.8 & 1.9 Ran on CGI with apache Method shelter improved performance !! ◦ Why?

Why shelter made tDiary fast String#method_missing issue “require” calls its arg’s to_path method if defined ◦ If arg’s method_missing is defined, try to call it ◦ String#method_missing slows “require” Method shelter restrict its negative effect

Other Usage:protect optimized methods In ruby, + - * / … are optimized ◦ only if they are not redefined ◦ Redefinition slows programs Method shelters can confine effect of redefinition Method shelter can improve performance

Other Usage:shelter-private accessor Ruby has no private instance variables A method shelter can mimic private ivars ◦ by generating unique name ◦ Accessible within the defined shelter and visible shelters

class Module def shelter_accessor(name) define_method name do ivname=get_unique_name(name) self.instance_variable_get(ivname) end define_method( (name.to_s+"=").to_sym) do|val| ivname= get_unique_name(name) self.instance_variable_set(ivname,val) end endend

Conclusion Open class is dangerous Method shelters resolving conflicts ◦ With hidden methods, hiddenly importing I implemented in Ruby ◦ Not so slow (個人的な感覚) For more details or the source code, ◦ wait for the acceptance of my paper  Deadline: 2.days.since

Questions?

時間が余ったら

Global

 In my lookup algorithm, ◦ Shelter must have up to one parent For simpler semantics For efficient implementation

before C B A

after C’ C’’ B A

Method Shelters : Another Way to Resolve Class Extension Conflicts

by S Akai on Feb 03, 2012

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Method Shelters : Another Way to Resolve Class Extension Conflicts — Presentation Transcript