From: "skhrshin (Shintaro Sakahara) via ruby-core" <ruby-core@...>
Date: 2024-05-13T04:33:49+00:00
Subject: [ruby-core:117852] [Ruby master Bug#20485] Simple use of Fiber makes GC leak objects with singleton method

Issue #20485 has been updated by skhrshin (Shintaro Sakahara).


Do you mean this is fixed in trunk? Or are you saying this shouldn't happen on Ruby 3.3.1? If latter, that is not correct as I wrote `[1].each` and `Mutex.new.synchronize` versions reproduce the problem on Ruby 3.3.1.
I would like you to reopen this issue. Should I update `ruby -v` to `3.3.1 (2024-04-23 revision c56cd86388) [x86_64-linux]` here, or should I create a new issue?

----------------------------------------
Bug #20485: Simple use of Fiber makes GC leak objects with singleton method
https://bugs.ruby-lang.org/issues/20485#change-108260

* Author: skhrshin (Shintaro Sakahara)
* Status: Closed
* ruby -v: ruby 3.2.4 (2024-04-23 revision af471c0e01) [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
I found a possible memory leak which occurs only when several conditions are met.

The code to reproduce the problem is below:

```
class Work
  def add_method
    singleton_class.define_method(:f) {}
  end
end

1.times { Fiber.new {}.resume }

work = Work.new
work.add_method
work = nil
GC.start

num_objs = ObjectSpace.each_object.select { |o| o.is_a?(Work) rescue false }.size
unless num_objs.zero?
  raise "NG"
end
```

Expected result: The script exits normally.
Actual result: RuntimeError "NG" is raised.

If I change `1.times { Fiber.new {}.resume }` to just `Fiber.new {}.resume` or remove `work.add_method`, GC works as expected.
Is there any problem at the way to use Fiber in this code, or is it a bug due to Ruby?

I tested ruby 3.3.1 (2024-04-23 revision c56cd86388) [x86_64-linux] too and the result was a little different. The code above didn't reproduce the problem, but if I changed `1.times` to `Mutex.new.synchronize`, it was able to reproduce.



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