Bug #22064: GC compaction breaks compare-by-identity sets

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.3: DONTNEED, 3.4: DONTNEED, 4.0: DONE

[peterzhu2118 (Peter Zhu)]

GitHub PR: https://github.com/ruby/ruby/pull/16923

Compare-by-identity sets use the address for hashing, so we must pin it so the object does not move in GC compaction. Objects in a compare-by-identity set is not currently pinned, causing the set to be broken if the object is moved.

For example:

set = Set.new.compare_by_identity

o = Object.new
set.add(o)

puts set.include?(o)

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

puts set.include?(o)

It should output true twice, but it outputs true and false.

[peterzhu2118 (Peter Zhu)]

• Status changed from Open to Closed

Applied in changeset git|baec5bbfffb38083b4180240a0319d20c9afc2a7.

---

Fix GC compaction for compare-by-identity sets

[Bug #22064]

Compare-by-identity sets use the address for hashing, so we must pin it
so the object does not move in GC compaction. Objects in a compare-by-identity
set is not currently pinned, causing the set to be broken if the object
is moved.

For example:

set = Set.new.compare_by_identity

o = Object.new
set.add(o)

puts set.include?(o)

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

puts set.include?(o)

It should output true twice, but it outputs true and false.

[k0kubun (Takashi Kokubun)]

• Backport changed from 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED to 3.3: DONTNEED, 3.4: DONTNEED, 4.0: DONE

ruby_4_0 1f3a2c5db2a45180980cdc6d2f283c077c8b3644.