A Wait-free Multi-word Atomic (1,N) Register for Large-scale Data Sharing on Multi-core Machines

TL;DR

This paper introduces ARC, a wait-free multi-word atomic register for multi-core systems that supports over 4 billion concurrent readers, improves scalability, and maintains constant-time read/write operations, suitable for cloud environments.

Contribution

ARC is a novel wait-free multi-word register that significantly increases reader capacity and reduces memory copying, enhancing scalability and performance on multi-core machines.

Findings

Supports up to 2^{32}-2 readers on 64-bit systems

Achieves constant-time reads and amortized constant-time writes

Demonstrates resilience in virtualized cloud environments

Abstract

We present a multi-word atomic (1,N) register for multi-core machines exploiting Read-Modify-Write (RMW) instructions to coordinate the writer and the readers in a wait-free manner. Our proposal, called Anonymous Readers Counting (ARC), enables large-scale data sharing by admitting up to $2^{32}-2$ concurrent readers on off-the-shelf 64-bits machines, as opposed to the most advanced RMW-based approach which is limited to 58 readers. Further, ARC avoids multiple copies of the register content when accessing it---this affects classical register's algorithms based on atomic read/write operations on single words. Thus it allows for higher scalability with respect to the register size. Moreover, ARC explicitly reduces improves performance via a proper limitation of RMW instructions in case of read operations, and by supporting constant time for read operations and amortized constant time for write operations. A proof of correctness of our register algorithm is also provided, together with experimental data for a comparison with literature proposals. Beyond assessing ARC on physical platforms, we carry out as well an experimentation on virtualized infrastructures, which shows the resilience of wait-free synchronization as provided by ARC with respect to CPU-steal times, proper of more modern paradigms such as cloud computing.