[ruby-core:102196] [Ruby master Bug#17543] Ractor isolation broken by `self` in shareable proc

Issue #17543 has been updated by Eregon (Benoit Daloze).


I think conceptually sharing the self would be cleaner/simpler/consistent-with-captures-vars, but I agree in practice that's rarely wanted.
So changing the receiver to something like `Ractor::DETACHED_SELF` is probably the most convenient.

MaxLap (Maxime Lapointe) wrote in #note-7:
> And if the person does want to go the make self sharable way, it's easy and clear:
> ```
> Ractor.make_shareable(self)
> other_ractor.send([:use_this_block, Ractor.make_shareable(proc { |k| k << value})])
> ```

Ah, so `Ractor.make_shareable` would use the existing receiver if shareable and `Ractor::DETACHED_SELF` otherwise?
That seems nice e.g. for a block in a class method, where the class itself is shareable.
It might lead to some confusion to have such dynamic behavior though, which also depends on whether `self` was made shareable at some point.

----------------------------------------
Bug #17543: Ractor isolation broken by `self` in shareable proc
https://bugs.ruby-lang.org/issues/17543#change-90043

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: 3.0.0p0
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
Discussing with @MaxLap we realized that the `self` in a shareable proc is not properly isolated:

```
class Foo
  attr_accessor :x

  def pr
    Ractor.make_shareable(Proc.new { self })
  end
end

f = Foo.new
f.x = [1, 2, 3]
Ractor.new(f.pr) { |pr| pr.call.x << :oops }
p f.x # => [1, 2, 3, :oops]
```

If the `self` refers to a shareable object then it's fine, but for non-shareable objects it has to be reset to `nil` or to a global shareable object that would have an instructive `inspect`.

```ruby
Ractor::DETACHED_SELF = Object.new
def << Ractor::DETACHED_SELF
  def inspect
    '<#detached self>'
  end
  alias to_s inspect
end
Ractor::DETACHED_SELF.freeze
```




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