SoK: Concurrency in Blockchain -- A Systematic Literature Review and the Unveiling of a Misconception

TL;DR

This paper systematically reviews concurrency in blockchain smart contracts, highlighting a major misconception, analyzing vulnerabilities, and proposing a taxonomy to guide future research for secure and efficient blockchain systems.

Contribution

It provides the first comprehensive survey of concurrency in blockchain, introduces a taxonomy, uncovers a widespread misconception, and outlines future research directions.

Findings

Revealed a flawed concurrency assumption in major research.

Identified key vulnerabilities and attack vectors.

Outlined solutions and future research gaps.

Abstract

Smart contracts, the cornerstone of blockchain technology, enable secure, automated distributed execution. Given their role in handling large transaction volumes across clients, miners, and validators, exploring concurrency is critical. This includes concurrent transaction execution or validation within blocks, block processing across shards, and miner competition to select and persist transactions. Concurrency and parallelism are a double-edged sword: while they improve throughput, they also introduce risks like race conditions, non-determinism, and vulnerabilities such as deadlock and livelock. This paper presents the first survey of concurrency in smart contracts, offering a systematic literature review organized into key dimensions. First, it establishes a taxonomy of concurrency levels in blockchain systems and discusses proposed solutions for future adoption. Second, it examines vulnerabilities, attacks, and countermeasures in concurrent operations, emphasizing the need for correctness and security. Crucially, we reveal a flawed concurrency assumption in a major research category, which has led to widespread misinterpretation. This work aims to correct that and guide future research toward more accurate models. Finally, we identify gaps in each category to outline future research directions and support blockchain's advancement.