No, we didn't cheat in the benchmark. At least I hope we didn't. Every optimization in this story was gated on bit identical output checksums against HotSpot, and the harness refuses to print a ratio when a checksum differs. If anything, this post is about how good HotSpot actually is. We tilted the table in our favor in every way we could, we hand tuned C code, and we still only beat it on some benchmarks. Getting there was a genuine struggle. If you want to understand the nuts and bolts of what your Java code costs, and the tradeoffs each runtime picks, I hope this is a good read.
What is Codename One? Codename One is an open-source framework for building native iOS, Android, desktop, and web apps from a single Java or Kotlin codebase. Learn more at codenameone.com.
The short version: PR #5327 takes ParparVM, the AOT VM that compiles your Java bytecode to C for iOS and other targets, from 4.21x slower than warmed Java 25 to geomean 1.00x parity across a ten benchmark suite, with six of the ten at or below HotSpot. Along the way you'll meet a new page based heap, a poor man's Project Valhalla, code generation that finally lets clang do its job, and two places where HotSpot beat our hand written C anyway. The memory story ends even better than the speed story.
