Landing: 4b690722a058
Project / Subsystem
gcc / libstdc++
Date
2026-05-05
Author
Jonathan Wakely
Commit
4b690722a0585c50f033deec5637760a671c72f0
Source
github
Perf win
Yes
Breaking
No
All attributes
- project
- gcc
- subsystem
- libstdc++
- patch_id
- —
- commit_hash
- 4b690722a0585c50f033deec5637760a671c72f0
- source_type
- github
- headline
- libstdc++: Use proper hash function for atomic::wait state [PR115955]
- tldr
- Improves std::atomic::wait performance and correctness by using a better hash function for wait state lookups.
- author
- Jonathan Wakely
- outcome
- committed
- performance_win
- true
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • libstdc++
- • concurrency
- • performance
- • bugfix
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-05-05T00:00:00.000Z
The hash function used for managing wait states in std::atomic::wait has been improved to reduce collisions and pathological behavior. The previous hashing scheme led to frequent collisions, causing incorrect wakeups and performance degradation, especially under high thread contention. The new hash function provides better distribution and uses a per-process seed for increased uniqueness.