Bug #20868: Method#hash changes after compaction

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.1: WONTFIX, 3.2: DONE, 3.3: REQUIRED

[peterzhu2118 (Peter Zhu)]

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:

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

[peterzhu2118 (Peter Zhu)]

• Backport changed from 3.1: UNKNOWN, 3.2: REQUIRED, 3.3: REQUIRED to 3.1: WONTFIX, 3.2: REQUIRED, 3.3: REQUIRED

[peterzhu2118 (Peter Zhu)]

• Status changed from Open to Closed

Applied in changeset git|56ecc243e230e8e99761ec0ffc5116601f094bb0.

---

[Bug #20868] Fix Method#hash to not change after compaction

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

For example:

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

[nagachika (Tomoyuki Chikanaga)]

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

ruby_3_2 ee3428aa0e3a11ed1574b7d99222f6f08737f818 merged revision(s) 56ecc243e230e8e99761ec0ffc5116601f094bb0.