JCTools
High-performance concurrent data structures for the JVM, supplementing the Java standard library.
What is JCTools?
JCTools is a Java library that provides high-performance concurrent data structures, specifically queues, which are not available in the standard JDK. It solves the need for efficient, lock-free multi-threaded communication in applications where the built-in Java collections fall short on performance or concurrency patterns.
Java developers building high-throughput, low-latency systems such as networking frameworks, data processing pipelines, or real-time applications that require optimized multi-producer/multi-consumer queues.
Developers choose JCTools for its proven performance, stability, and adoption by major projects like Netty and RxJava. It offers a free, open-source alternative with specialized queue implementations that outperform standard JDK options in concurrent scenarios.
Overview
JCTools provides a collection of concurrent data structures that are missing from the Java Development Kit (JDK). It offers high-performance, lock-free queues and utilities designed for demanding multi-threaded applications, used by major frameworks like Netty and RxJava.
Key Features
- SPSC/MPSC/SPMC/MPMC Queues — Wait-free or lock-less concurrent queues for various producer-consumer patterns (Single/Multi Producer, Single/Multi Consumer).
- Linked Array Queues — Bounded and unbounded queues balancing performance, memory allocation, and footprint.
- XAdd-Based Queues — Unbounded linked array queues using XADD to reduce producer contention and pooled chunks to minimize allocation.
- Expanded Queue Interface —
MessagePassingQueuewith relaxed offer/peek/poll for performance trade-offs and batch drain/fill methods for higher throughput. - Implementation Variations — Queues available in
Unsafe(default),Atomic(usingAtomicFieldUpdater), andUnpadded(reduced memory footprint) versions.
Philosophy
JCTools focuses on delivering excellent performance at zero cost (free under Apache 2.0 License) while maintaining stability and community-driven development.
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