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Bug #4181

closed

Backport Ruby 1.9 singleton.rb, since 1.8's is not thread-safe

Added by headius (Charles Nutter) over 13 years ago. Updated almost 11 years ago.

Status:
Closed
Target version:
ruby -v:
Any Ruby 1.8 version
[ruby-core:33796]

Description

=begin
Ruby 1.9 modified singleton.rb by eliminating much of the lazy init logic, using a real mutex instead of Thread.critical, and eliminating the redefinition of "instance" on first call. None of these changes have been backported into a 1.8 release, which means all 1.8 releases have a broken singleton.rb.

The following script breaks under any version of 1.8:

require 'singleton' $jruby = RUBY_PLATFORM =~ /java/ require 'jruby/synchronized' if $jruby

loop do
$inits = []
$inits.extend JRuby::Synchronized if $jruby
classes = []
1000.times do
classes << Class.new do
include Singleton
end
end

(0..10).map do
  Thread.new do
    classes.each do |cls|
      cls.instance
    end
  end
end.map(&:join)
puts "loop completed"

end

Results:

~/projects/jruby ➔ ruby -v singleton_killer.rb
ruby 1.8.7 (2010-08-16 patchlevel 302) [i686-darwin10.4.0]
loop completed
loop completed
loop completed
loop completed
loop completed
loop completed
loop completed
loop completed
loop completed
singleton_killer.rb:18: undefined method instance' for #<Class:0x1001896a0> (NoMethodError) from singleton_killer.rb:1:in join'
from singleton_killer.rb:1:in to_proc' from singleton_killer.rb:21:in map'
from singleton_killer.rb:21
from singleton_killer.rb:5:in `loop'
from singleton_killer.rb:5

~/projects/jruby ➔ ruby -v singleton_killer.rb
ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]
loop completed
loop completed
loop completed
loop completed
singleton_killer.rb:18: undefined method instance' for #<Class:0x100348c70> (NoMethodError) from singleton_killer.rb:1:in join'
from singleton_killer.rb:1:in to_proc' from singleton_killer.rb:21:in map'
from singleton_killer.rb:21
from singleton_killer.rb:5:in `loop'
from singleton_killer.rb:5

This can lead to lazy failures in any library that uses singleton.rb. See also this commit to Nokogiri, where they had to stop using Singleton because of this issue:

https://github.com/tenderlove/nokogiri/commit/5eb036e39ea85a8e12eebee11bc5086b0e4ce6e3
=end

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