Transactional Sapphire: Lessons in High-Performance, On-the-fly Garbage Collection

• Published in: ACM transactions on programming languages and systems 2018-12, Vol.40 (4), p.1-56, Article 15
• Main Authors: Ugawa, Tomoharu, Ritson, Carl G., Jones, Richard E.
• Format: Article
• Language: English
• Subjects: Compilers; General programming languages; Language types; Object oriented languages; Runtime environments; Software and its engineering; Software notations and tools
• ISSN: 0164-0925; 1558-4593
• DOI: 10.1145/3226225

Constructing a high-performance garbage collector is hard. Constructing a fully concurrent ‘on-the-fly’ compacting collector is much more so. We describe our experience of implementing the Sapphire algorithm as the first on-the-fly, parallel, replication copying, garbage collector for the Jikes RVM Java virtual machine (JVM). In part, we explain our innovations such as copying with hardware and software transactions, on-the-fly management of Java’s reference types, and simple, yet correct, lock-free management of volatile fields in a replicating collector. We fully evaluate, for the first time, and using realistic benchmarks, Sapphire’s performance and suitability as a low latency collector. An important contribution of this work is a detailed description of our experience of building an on-the-fly copying collector for a complete JVM with some assurance that it is correct. A key aspect of this is model checking of critical components of this complicated and highly concurrent system.