Reciprocating Locks

TL;DR

Reciprocating Locks is a new mutual exclusion algorithm for shared memory systems that offers constant-time operations, low contention latency, and strong anti-starvation guarantees, suitable for real-world applications.

Contribution

It introduces a lock with constant-time doorway and release phases, local spinning, and strong anti-starvation properties, optimized for practical use in systems like Linux kernel and pthreads.

Findings

High throughput under contention

Low latency in uncontended scenarios

Competitive performance with state-of-the-art spin locks

Abstract

We present "Reciprocating Locks", a novel mutual exclusion locking algorithm, targeting cache-coherent shared memory (CC), that enjoys a number of desirable properties. The doorway arrival phase and the release operation both run in constant-time. Waiting threads use local spinning and only a single waiting element is required per thread, regardless of the number of locks a thread might hold at a given time. While our lock does not provide strict FIFO admission, it bounds bypass and has strong anti-starvation properties. The lock is compact, space efficient, and has been intentionally designed to be readily usable in real-world general purpose computing environments such as the linux kernel, pthreads, or C++. We show the lock exhibits high throughput under contention and low latency in the uncontended case. The performance of Reciprocating Locks is competitive with and often better than the best state-of-the-art scalable spin locks.