From: "sam.saffron (Sam Saffron)" <sam.saffron@...>
Date: 2013-10-04T15:38:12+09:00
Subject: [ruby-core:57662] [ruby-trunk - Feature #8977] String#frozen that	takes advantage of the deduping


Issue #8977 has been updated by sam.saffron (Sam Saffron).


@nobu 

You can implement a separate string pool in 2.0 using like so:

require 'weakref'

class Pool
  def initialize
    @pool = {}
  end
  def get(str)
    ref = @pool[str]

    # GC may run between alive? and __getobj__
    copy = ref && ref.weakref_alive? && copy = ref.__getobj__ rescue nil
    unless copy
      copy=str.dup
      ref=WeakRef.new(copy)
      copy.freeze
      @pool[str] = ref
    end
    copy
  end

  def scrub!
    GC.start
    @pool.delete_if{|k,v| v.nil?}
  end

  def length
    @pool.length
  end
end

@pool = Pool.new
def test
  puts @pool.get("test").object_id
end

test #69822933011880
test #69822933011880

p @pool.length #1

@pool.scrub!

test #69822914568080
test #69822914568080

p @pool.length #1

but the disadvantage is that it is fiddely, requires manual management and will not reuse FrozenTable
----------------------------------------
Feature #8977: String#frozen that takes advantage of the deduping 
https://bugs.ruby-lang.org/issues/8977#change-42280

Author: sam.saffron (Sam Saffron)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: current: 2.1.0


During memory profiling I noticed that a large amount of string duplication is generated from non pre-determined strings.

Take this report for example https://gist.github.com/SamSaffron/6789005 (generated using the memory_profiler gem that works against head) 

">=" x 4953
    /Users/sam/.rbenv/versions/2.1.0-dev/lib/ruby/2.1.0/rubygems/requirement.rb:93 x 4535

This string is most likely extracted from a version. 

Or 

"/Users/sam/.rbenv/versions/2.1.0-dev/lib/ruby/gems" x 5808
    /Users/sam/.rbenv/versions/2.1.0-dev/lib/ruby/gems/2.1.0/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251 x 3894

A string that can not be pre-determined. 

---- 


It would be nice to have 

"hello,world".split(",")[0].frozen.object_id == "hello"f.object_id 

Adding #frozen will give library builders a way of using the de-duping. It also could be implemented using weak refs in 2.0 and stubbed with a .dup.freeze in 1.9.3 . 

Thoughts ?  





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