TRANSACTIONAL SAPPHIRE Tomoharu Ugawa, Kochi University of Technology, Japan Carl Ritson, University of Kent, UK Richard Jones, University of Kent, UK This is ahigh-performance implementation of the Sapphire GC algorithm [1,4]. It is the first on-the-fly, parallel, replication copying, garbage collector for the Jikes RVM Java virtual machine. The implementation provides innovations such as copying with hardware or 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. * The jikesrvm directory provides the source code for the Jikes RVM including the Sapphire GC. * The models directory above provides SPIN models  of critical components of this complicated and highly concurrent system. For convenience, copies of our relevant published papers are here too:  TOPLAS4004-15 final.pdf Tomoharu Ugawa, Carl Ritson and Richard Jones (2018). Transactional Sapphire: Lessons in High Performance, On-the-fly Garbage Collection. ACM Transactions on Programming Languages and Systems (TOPLAS), 40 (4). https://doi.org/10.1145/3226225  ismm021-ritson.pdf Carl G. Ritson, Tomoharu Ugawa and Richard Jones (2014). Exploring Garbage Collection with Haswell Hardware Transactional Memory. International Symposium on Memory management. https://doi.org/10.1145/2602988.2602992  ismm012-ugawa.pdf Tomoharu Ugawa, Richard Jones and Carl G. Ritson (2014). Reference Object Processing in On-The-Fly Garbage Collection. International Symposium on Memory Management. https://doi.org/10.1145/2602988.2602991 Other relevant publications:  Richard L. Hudson and J. Eliot B. Moss (2003). Sapphire: Copying Garbage Collection Without Stopping the World. Concurrency and Computation: Practice and Experience 15, 3–5 (2003), 223–261. https://doi.org/10.1002/cpe.712  G. J. Holzmann (2004). The SPIN Model Checker: Primer and Reference Manual. Addison-Wesley.