[ruby-core:101183] [Ruby master Bug#17359] Ractor copy mode is not Ractor-safe

Issue #17359 has been updated by ko1 (Koichi Sasada).


Dan0042 (Daniel DeLorme) wrote in #note-3:
> The `initialize_copy` is executed in the main ractor, that's why it can set a global variable. It should be executed in the sub-ractor I think.

It is not acceptable because the src object is accessed from main and sub (`initialize_copy`) simultaneously.


----------------------------------------
Bug #17359: Ractor copy mode is not Ractor-safe
https://bugs.ruby-lang.org/issues/17359#change-88865

* 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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