Concurrent Reference Counting and Resource Management in Wait-free Constant Time

TL;DR

This paper introduces a novel acquire-retire interface for concurrent resource management that ensures safe, lock-free access with constant time overhead, improving efficiency in memory reclamation, reference counting, and object management.

Contribution

It presents a new acquire-retire interface enabling lock-free, constant-time resource protection in concurrent programs, with applications to memory reclamation, reference counting, and object management.

Findings

Expected constant time overhead for all operations.

Significant improvements over previous methods in memory reclamation and reference counting.

Original application to object management with moves, copies, and destructs.

Abstract

A common problem when implementing concurrent programs is efficiently protecting against unsafe races between processes reading and then using a resource (e.g., memory blocks, file descriptors, or network connections) and other processes that are concurrently overwriting and then destructing the same resource. Such read-destruct races can be protected with locks, or with lock-free solutions such as hazard-pointers or read-copy-update (RCU). In this paper we describe a method for protecting read-destruct races with expected constant time overhead, $O(P^2)$ space and $O(P^2)$ delayed destructs, and with just single word atomic memory operations (reads, writes, and CAS). It is based on an interface with four primitives, an acquire-release pair to protect accesses, and a retire-eject pair to delay the destruct until it is safe. We refer to this as the acquire-retire interface. Using the acquire-retire interface, we develop simple implementations for three common use cases: (1) memory reclamation with applications to stacks and queues, (2) reference counted objects, and (3) objects manage by ownership with moves, copies, and destructs. The first two results significantly improve on previous results, and the third application is original. Importantly, all operations have expected constant time overhead.