0-1-4-understand-mcs-lock

name	0.1.4-understand-mcs_lock
description	[0.1.4] Queued lock where each waiting thread spins on a locally-owned node linked into a queue; cache-friendly with o

understand-mcs_lock

CALL NUMBER: concurrency_synchronization_primitives_and_memor.mcs_lock DEFINITION: Queued lock where each waiting thread spins on a locally-owned node linked into a queue; cache-friendly with only O(1) bus traffic per lock acquisition; named after Mellor-Crummey and Scott.

Invoke this skill to understand mcs_lock 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.
• atomic_exchange (d1): Atomic operation that reads the current value of a variable and writes a new value in a single indivisible step, returning the old value.
• memory_order_acquire (d1): Memory ordering barrier ensuring all loads and stores after the barrier in program order cannot be reordered before it, synchronizing with release stores.
• memory_order_release (d1): Memory ordering barrier ensuring all loads and stores before the barrier in program order cannot be reordered after it, making prior writes visible to acquiring threads.

CONSUMERS (what needs this)

clh_lock, spinlock

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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.)