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mruby-weakref

(日本語で書かれた原文 / Written original README in Japanese)

A weak reference object available on mruby.

I'm trying to mimic the CRuby standard attachment library weakref.

Inspired by How to weakly reference a mrb_value in C++ #4479 and created.

How to install

Build mruby by adding it as a gem to build_config.rb.

MRuby::Build.new do |conf|
  conf.gem "mruby-weakref", github: "dearblue/mruby-weakref"
end

If you want to depend on the mruby gem package, write it in mrbgem.rake.

# mrbgem.rake
MRuby::Gem::Specification.new("mruby-XXX") do |spec|
  ...
  spec.add_dependency "mruby-weakref", github: "dearblue/mruby-weakref"
end

How to use

Maybe it works as https://docs.ruby-lang.org/ja/latest/library/weakref.html ... hopefully.

  • Sample code (example.rb):

    def makeref
      target = [*"A".."Z"]
      ref = WeakRef.new(target)
      puts ref.inspect
      ref
    end
    
    ref = makeref
    p ref.weakref_alive?
    20.times { GC.start }
    p ref.weakref_alive?
    p ref.__getobj__
  • run with mruby:

    % ./build/host/bin/mruby example.rb
    ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
    true
    nil
    trace (most recent call last):
            [0] example.rb:12
    example.rb:12: Invalid Reference - probably recycled (WeakRef::RefError)
    
  • run with ruby-2.6.3:

    % ruby26 -r weakref example.rb
    ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
    true
    nil
    Traceback (most recent call last):
    example.rb: Invalid Reference - probably recycled (WeakRef::RefError)
    

About the implementation method

Please see HOW_TO_IMP.md for implementation method.

Specification

  • Package name: mruby-weakref
  • Version: 0.1
  • Product quality: CONCEPT
  • Author: dearblue
  • Project page: https://github.com/dearblue/mruby-weakref
  • Licensing: Creative Commons Zero License (CC0; likely Public Domain)
  • Required mruby version: 1.4.0 or later
  • Object code size: About 4 Ki bytes on FreeBSD 12.0 AMD64 with clang
  • Heap usages per one weakref instance on FreeBSD 12.0 AMD64 (rough estimate for string object):
    • 48 bytes: weakref object
    • 20×N bytes: delegated method table (N is count of string methods (probably more than 160))
    • 48 + 32 bytes: capture object
    • 48 bytes: singleton class
    • 144 bytes (?): instance variable table
    • 48 bytes: array for back reference
    • 3500+ bytes: total
  • Dependency external mrbgems:
  • Bundled C libraries (git-submodules): (NONE)

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`WeakRef` implementation for mruby

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