[ruby-core:102305] [Ruby master Feature#17592] Ractor should allowing reading shareable class instance variables
From:
marcandre-ruby-core@...
Date:
2021-01-29 15:29:20 UTC
List:
ruby-core #102305
Issue #17592 has been reported by marcandre (Marc-Andre Lafortune).
----------------------------------------
Feature #17592: Ractor should allowing reading shareable class instance variables
https://bugs.ruby-lang.org/issues/17592
* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
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It would be very helpful if Ractor was allowing reading class instance variables from non-main Ractor.
Currently is raises an IsolationError:
```ruby
module Foo
singleton_class.attr_accessor :config
Foo.config = {example: 42}.freeze
end
Ractor.new { p Foo.config } # => IsolationError
```
This limitation makes it challenging to have an efficient way to store general configs, i.e. global data that mutated a few times when resources get loaded but it immutable afterwards, and needs to be read all the time.
Currently the only way to do this is to use a constant and use `remove_const` + `const_set` (which can not be made atomic easily).
I think that allowing reading only may be the best solution to avoid any race condition, e.g. two different Ractors that call `@counter += 1`.
The only 3 scenarios I see here are:
0) declare the constant hack the official way to store config-style data
1) allow reading of instance variables for shareable objects (as long as the data is shareable)
2) allow read-write
I prefer 1)
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