Thomas Enebo

Rubyists work from a command line, which makes JRuby startup time a critical concern. Traditionally, the JVM has not been optimized for startup, but that's changing. This talk will explore all available options for making a heavy runtime like JRuby start up quickly, from using class data caching services like Hotspot's CDS and OpenJ9's Quickstart to ahead-of-time compilation of JRuby using GraalVM's Native Image. We'll compare approaches and trade-offs.

JRuby has been compatible with various Ruby versions during its lifespan, ranging from the 1.6 series through today's 2.4. JRuby has supported Rails in some capacity since the 1.0 days. And at the same time, we've continued to improve performance. In this talk we'll explore JRuby's level of compatibility today and discuss the challenges of keeping up with an actively-developed language and ecosystem.

JRuby has for years routed around the JVM, to maximize compatibility with standard Ruby. We've implemented byte[]-based String and Regexp, native POSIX support, and our own mixed-mode interpreting/jitting runtime atop JVM bytecode.

With JRuby 9000, we're taking this even further. JRuby 9000 introduces a new IR-based optimizing compiler, with inlining, specialization, and other tricks applied to both interpreted and bytecode-compiled code. We've also gone fully native for much of IO and Process management. This talk will show the state of this work and how it affects JRuby and the wider JVM world.