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:
  • mruby-delegate
• Bundled C libraries (git-submodules): (NONE)