[ruby-core:121468] [Ruby Feature#17414] Ractor should allow access to shareable attributes for Modules/Classes

28 Mar 2025

      Issue #17414 has been updated by jhawthorn (John Hawthorn).

Status changed from Assigned to Closed

I think we can close this as accessing the class instance variables has been allowed for a while (Ruby 3.1?)

``` ruby
module Config
  class << self
    attr_accessor :conf
  end
  self.conf = 42
end

Ractor.new { Config.conf = 66 }.take # => can not set instance variables of classes/modules by non-main Ractors (Ractor::IsolationError)
Ractor.new { puts Config.conf }.take # => 42
```

----------------------------------------
Feature #17414: Ractor should allow access to shareable attributes for Modules/Classes
https://bugs.ruby-lang.org/issues/17414#change-112475

* Author: marcandre (Marc-Andre Lafortune)
* Status: Closed
* Assignee: ko1 (Koichi Sasada)
----------------------------------------
Current situation is *very* limiting.

Use-case: global config.

Example: [yaml has a global config](https://github.com/ruby/psych/blob/master/lib/psych.rb#L637-L640) and it's not clear to me how to make that Ractor-aware (nicely).

It is possible to have the same effect but in ugly ways:

```ruby
# Using instance variables of Module not allowed:

module Config
  class << self
    attr_accessor :conf
  end
  self.conf = 42
end

Ractor.new { Config.conf = 66 }.take # => can not access instance variables from non-main Ractors
Ractor.new { puts Config.conf }.take # => can not access instance variables from non-main Ractors

# Same functionality using constants allowed:
module Config
  class << self
    def conf
      CONF
    end

    def conf=(new_conf)
      remove_const(:CONF)
      const_set(:CONF, new_conf)
    end
  end
  CONF = 42
end

Ractor.new { Config.conf = 66 }.take # => ok
Ractor.new { puts Config.conf }.take # => 66

# Same functionality using methods allowed:
module Config
  class << self
    def conf
      42
    end

    def conf=(new_conf)
      singleton_class.undef_method(:conf)
      define_singleton_method(:conf, &Ractor.make_shareable(Proc.new { new_conf }))
    end
  end
end

Ractor.new { Config.conf = 66 }.take # => ok
Ractor.new { puts Config.conf }.take # => 66
```

The priority would be to allow reading these instance variables if they are shareable. Ideally writing would also be allowed, but limiting that to main ractor is less probablematic than with reading.

-- 
https://bugs.ruby-lang.org/