[ruby-core:101202] [Ruby master Bug#17359] Ractor copy mode is not Ractor-safe

Issue #17359 has been updated by Dan0042 (Daniel DeLorme).


ko1 (Koichi Sasada) wrote in #note-6:
> One idea is prohibit `initialize_copy` written in Ruby, for ractor_copy.
> But I'm not sure how it is feasible.
> 
> ```
> ko1@aluminium:~$ gem-codesearch 'def initialize_clone' | wc -l
> 120
> ko1@aluminium:~$ gem-codesearch 'def initialize_copy' | wc -l
> 3430
> ```

I think it's feasible. `initialize_clone` and `initialize_copy` are mostly (only?) used because `clone` and `dup` only perform shallow copies. See the examples below. Since ractor-copy already performs a deep-copy, the extra copy/cloning in these examples is redundant. Actually... it's buggy? Since the `initialize_clone` is executed in the parent ractor, the objects are created as part of the parent ractor's heap rather than the child ractor's heap?


```
activemodel-6.0.0/lib/active_model/attribute_set.rb
72:    def initialize_clone(_)
73-      @attributes = attributes.clone
74-      super
75-    end

regexp_parser-1.6.0/lib/regexp_parser/expression/classes/group.rb
36:      def initialize_clone(orig)
37-        @name = orig.name.dup
38-        super
39-      end
40-    end

regexp_parser-1.6.0/lib/regexp_parser/expression/quantifier.rb
15:    def initialize_clone(orig)
16-      @text = orig.text.dup
17-      super
18-    end

regexp_parser-1.6.0/lib/regexp_parser/expression/subexpression.rb
15:    def initialize_clone(orig)
16-      self.expressions = orig.expressions.map(&:clone)
17-      super
18-    end

regexp_parser-1.6.0/lib/regexp_parser/expression.rb
24:    def initialize_clone(orig)
25-      self.text       = (orig.text       ? orig.text.dup         : nil)
26-      self.options    = (orig.options    ? orig.options.dup      : nil)
27-      self.quantifier = (orig.quantifier ? orig.quantifier.clone : nil)
28-      super
29-    end

actionpack-6.0.0/lib/action_controller/metal/strong_parameters.rb
1017:      def initialize_copy(source)
1018-        super
1019-        @parameters = @parameters.dup
1020-      end

actionpack-6.0.0/lib/action_dispatch/http/content_security_policy.rb
157:    def initialize_copy(other)
158-      @directives = other.directives.deep_dup
159-    end

actionpack-6.0.0/lib/action_dispatch/middleware/flash.rb
147:      def initialize_copy(other)
148-        if other.now_is_loaded?
149-          @now = other.now.dup
150-          @now.flash = self
151-        end
152-        super
153-      end

actionpack-6.0.0/lib/action_dispatch/middleware/stack.rb
95:    def initialize_copy(other)
96-      self.middlewares = other.middlewares.dup
97-    end

actionview-6.0.0/lib/action_view/path_set.rb
22:    def initialize_copy(other)
23-      @paths = other.paths.dup
24-      self
25-    end
```


----------------------------------------
Bug #17359: Ractor copy mode is not Ractor-safe
https://bugs.ruby-lang.org/issues/17359#change-88886

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 3.0.0dev (2020-11-30T10:06:25Z master 89774a938a) [x86_64-darwin18]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
It should not be possible to mutate an object across Ractors, but the copy mode allows it currently:

```ruby
class Foo
  attr_accessor :x

  def initialize_copy(*)
    $last = self
    super
  end
end
o = Foo.new
o.x = 42

r = Ractor.new(o) do |copy|
  puts copy.x # => 42
  Ractor.yield :sync
  Ractor.yield :sync
  puts copy.x # => 666
end
r.take # => :sync
$last.x = 666
r.take # => :sync
r.take
```

Maybe the `copy` object should be marked as moved?



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