0-4-3-understand-mcs-lock-enqueue

name	0.4.3-understand-mcs_lock_enqueue
description	[0.4.3] Operation appending a thread-local qnode to the queue tail; atomically CASes qnode into tail; on CAS failure,

understand-mcs_lock_enqueue

CALL NUMBER: deep_spinlock.mcs_lock_enqueue DEFINITION: Operation appending a thread-local qnode to the queue tail; atomically CASes qnode into tail; on CAS failure, completes the predecessor's link and retries; ensures FIFO acquisition order.

Invoke this skill to understand mcs_lock_enqueue down to its primitives. The RELATIVE ROOT below is the least-fixed-point closure of everything it bundles from — the full import cone, grouped by the lib each prim comes from. Projected from a prover-typed KB (MAP/SWI-Prolog consistency gate): every reference below resolves.

THE RELATIVE ROOT (the import cone, by lib)

from ?

• atomic_cas (d1): Compare-and-swap operation atomically loading a value, comparing it to an expected value, and storing a new value only if they matched, returning whether the swap occurred.

from deep_spinlock

• mcs_lock_help_links (d1): Backoff resolution protocol during failed enqueue CAS; the thread that lost the CAS follows the discovered pointer chain to complete the linking work of the winner before retrying its own append; prevents starvation under high contention.

CONSUMERS (what needs this)

mcs_lock_acquire, mcs_lock_fifo_ordering

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Projected from the concurrency synchronization primitives and memory models KB (155 concepts / 137 relations) — consistency-typed by MAP; the facet list after the colon IS the cross-lib dependency web.

(leaf — this is an actual skill.)