From: eregontp@...
Date: 2020-12-21T15:56:40+00:00
Subject: [ruby-core:101592] [Ruby master Feature#17414] Ractor should allow access to shareable attributes for Modules/Classes

Issue #17414 has been updated by Eregon (Benoit Daloze).


marcandre (Marc-Andre Lafortune) wrote in #note-2:
> Using `yaml/psych` should be doable easily in multiple Ractors, right?

Ideally, but I guess there might be many issues with existing gems and the restrictions of Ractor.

> Having the global config be per-Ractor would complicate the design for no gain.

It depends what you do with Ractor. If it was hosting multiple apps in the same process, it might make a lot of sense.

> At any point in time, the global config [...]

I think Ractor compatibility is a good opportunity to actually revisit whether things need to be global.

In many (all?) cases, it does not need to be global.
For instance, such  domain specific handlers could be passed explicitly to YAML.load/dump, which would be much clearer and cleaner.

----------------------------------------
Feature #17414: Ractor should allow access to shareable attributes for Modules/Classes
https://bugs.ruby-lang.org/issues/17414#change-89378

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* 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.



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