Constant Amortized RMR Abortable Mutex for CC and DSM

Abstract

The Abortable mutual exclusion problem, proposed by Scott and Scherer in response to the needs in real time systems and databases, is a variant of mutual exclusion that allows processes to abort from their attempt to acquire the lock. Worst-case constant remote memory reference (RMR) algorithms for mutual exclusion using hardware instructions such as Fetch&Add or Fetch&Store have long existed for both Cache Coherent (CC) and Distributed Shared Memory (DSM) multiprocessors, but no such algorithms are known for abortable mutual exclusion. Even relaxing the worst-case requirement to amortized, algorithms are only known for the CC model. In this paper, we improve this state-of-the-art by designing a deterministic algorithm that uses Fetch&Store (FAS) to achieve amortized O(1) RMR in both the CC and DSM models. Our algorithm supports Fast Abort (a process aborts within six steps of receiving the abort signal), and has the following additional desirable properties: it supports an arbitrary number of processes of arbitrary names, requires only O(1) space per process, and satisfies a novel fairness condition that we call "Airline FCFS''. Our algorithm is short and practical with fewer than a dozen lines of code.