From: "rm155 (Rohit Menon)" <noreply@...>
Date: 2021-08-23T22:05:18+00:00
Subject: [ruby-core:105057] [Ruby master Bug#18128] Ractor allows class variables that have been used before

Issue #18128 has been reported by rm155 (Rohit Menon).

----------------------------------------
Bug #18128: Ractor allows class variables that have been used before
https://bugs.ruby-lang.org/issues/18128

* Author: rm155 (Rohit Menon)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
In order to avoid data races, Ractor is not supposed to allow class variables. For example, the following code does not run:
``` ruby
class C
  def initialize
    @@var = 1
  end
end
Ractor.new do
  C.new
end.take
#=> can not access class variables from non-main Ractors (Ractor::IsolationError)

```

This error is expected because of Ractor's rules.


However, there appears to be a bug that lets class variables be accessed in Ractors if they have already been used in the main Ractor. For example, the following code does unexpectedly run:
``` ruby
class C
  def initialize
    @@var = 1
  end
end
C.new
Ractor.new do
  C.new
end.take
```


This program doesn���t detect the problem and runs without an error message. This could potentially pose problems, as it may allow class variables to remain unnoticed in Ractors, which could lead to a data race situation.



-- 
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