Concurrent Double-Ended Priority Queues

TL;DR

This paper introduces the first concurrent double-ended priority queue implementation, combining existing priority queues with a novel approach to support concurrent max and min extractions while maintaining lock-freedom.

Contribution

It presents a general method to add ExtractMax to concurrent priority queues and demonstrates a lock-free, dual-consumer DEPQ construction using linearizable single-consumer queues.

Findings

First concurrent DEPQ implementation.

Supports concurrent ExtractMax and ExtractMin operations.

Maintains lock-freedom in the construction.

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.