From: "k0kubun (Takashi Kokubun) via ruby-core" <ruby-core@...>
Date: 2025-01-15T01:40:44+00:00
Subject: [ruby-core:120676] [Ruby master Bug#20868] Method#hash changes after compaction

Issue #20868 has been updated by k0kubun (Takashi Kokubun).

Backport changed from 3.1: WONTFIX, 3.2: DONE, 3.3: REQUIRED to 3.1: WONTFIX, 3.2: DONE, 3.3: DONE

ruby_3_3 commit:42f043c1893b320b9d2a38ec3b1065dee71ce863 merged revision(s) commit:56ecc243e230e8e99761ec0ffc5116601f094bb0.

----------------------------------------
Bug #20868: Method#hash changes after compaction
https://bugs.ruby-lang.org/issues/20868#change-111499

* Author: peterzhu2118 (Peter Zhu)
* Status: Closed
* Backport: 3.1: WONTFIX, 3.2: DONE, 3.3: DONE
----------------------------------------
Fix: https://github.com/ruby/ruby/pull/12004

The hash value of a Method may change after a compaction but must remain constant because otherwise it may not work as the key in a hash table.

For example:

```ruby
def a; end

# Need this method here because otherwise the iseq may be on the C stack
# which would get pinned and not move during compaction
def get_hash
  method(:a).hash
end

puts get_hash # => 2993401401091578131

GC.verify_compaction_references(expand_heap: true, toward: :empty)

puts get_hash # => -2162775864511574135
```



-- 
https://bugs.ruby-lang.org/
 ______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/