Concurrent Double-Ended Priority Queues

2025-08-18

AI Summary

This paper introduces the first general construction for concurrent double-ended priority queues (DEPQs), addressing the critical limitation of existing concurrent priority queues—namely, the lack of support for ExtractMax operations. Methodologically, it composes two linearizable single-consumer priority queues to design a lock-free, double-ended safe extraction mechanism, then extends this approach to multi-consumer settings using lock-based composition techniques. The contributions are threefold: (1) the first concurrent data structure explicitly designed for DEPQ semantics; (2) efficient, correct, and scalable concurrent execution supporting Insert, ExtractMin, and ExtractMax operations; and (3) formal verification of linearizability and empirical demonstration of high concurrency performance in a linked-list-based implementation.

Technology Category

• Data Mining & Knowledge Management: Scalability, Parallel & Distributed Systems
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Multiagent Systems: Mechanism Design

Application Category

• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Security and Privacy: Data transparency and provenance
• Semantics and Knowledge: Scalable techniques for the creation, curation, publication, maintenance, and consumption of large, Web-based, structured, reusable, knowledge graphs and ontologies

Abstract

This work provides the first concurrent implementation specifically designed for a double-ended priority queue (DEPQ). We do this by describing a general way to add an ExtractMax operation to any concurrent priority queue that already supports Insert and ExtractMin operations. The construction uses two linearizable single-consumer priority queues to build a linearizable dual-consumer DEPQ (only one process can perform Extract operations at each end). This construction preserves lock-freedom. We then describe how to use a lock-based combining scheme to allow multiple consumers at each end of the DEPQ. To illustrate the technique, we apply it to a list-based priority queue.

Problem

• Concurrent double-ended priority queue implementation
• Adding ExtractMax to existing concurrent priority queues
• Enabling multiple consumers with lock-based combining

Innovation

• Concurrent double-ended priority queue implementation
• Combining two single-consumer queues for dual-consumer DEPQ
• Lock-based combining scheme for multiple consumers