Locking

Pick a PostgreSQL backend lock primitive (atomic / spinlock / LWLock / heavyweight / predicate / buffer-pin-content) or debug a lock-ordering bug, silent LWLock hang, deadlock-detector report, or a multixact / tuple-lock interaction — the six-layer PG lock taxonomy in operational form. Covers `pg_atomic_u32 / u64` ordering + memory barriers, `SpinLockAcquire / SpinLockRelease` (with the "no calls / no ereport / no CHECK_FOR_INTERRUPTS" rules), `LWLockAcquire LW_SHARED / LW_EXCLUSIVE` and tranches (lwlocklist.h + wait_event_names.txt), heavyweight `LockAcquire` / `LockRelationOid` / `LOCKTAG_*`, predicate (SSI) locks, buffer pin / content locks, the `BufferMapping / LockManager / PredicateLockManager` partition rank rules, multi-XID `HEAP_XMAX_IS_MULTI` interaction with `FOR UPDATE / FOR KEY SHARE`, parallel-worker lock-group semantics, and the lldb-attach recipe for silent-LWLock-deadlock diagnosis. **Use this skill proactively whenever the user is writing or reviewing C in `src/backend` or `dev/src/backend` that touches shared memory (MainLWLockArray, PGPROC, ProcArray, BufferDesc, SLRU, any `*Shmem*` allocation), adds a new LWLock tranche (RequestNamedLWLockTranche / LWLockNewTrancheId / PG_LWLOCK / PG_LWLOCKTRANCHE), picks between spinlock / LWLock / atomic / heavyweight for new shmem state, asks about LWLock partition rank order, debugs an LWLock hang where `pg_stat_activity` shows `wait_event_type='LWLock'` but no `deadlock detected` ever fires, hits an assertion like `IsRelationExtensionLockHeld`, gets bitten by `HEAP_XMAX_IS_MULTI` and GetMultiXactIdMembers, asks about parallel-worker lock-group conflicts, or reviews a patch that adds shmem state / new wait events — even when the user doesn't use the literal word "lock".** Skip for pthread_mutex_t / std::mutex / Java synchronized / ReentrantLock / Go sync.Mutex / Rust std::sync::Mutex / parking_lot / tokio::sync::Mutex / C# lock(obj) / Monitor.Enter, Redis pessimistic / Redlock / ZooKeeper / etcd / Chubby distributed locks, ORM optimistic locking (version int column), user-level / application-side `SELECT FOR UPDATE` design questions (how to model inventory claim), application-level lock-manager design (key→holder hash with TTLs), and general "what's the right lock primitive" non-PG advice.

mkdir -p ~/.claude/skills/locking
curl -L https://claudskills.com/skills/locking/SKILL.md \
  -o ~/.claude/skills/locking/SKILL.md

@misc{locking-2026,
  author    = {matejformanek},
  title     = {Locking [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/locking/}
}