I thought it was worth mentioning that another stealth research project at Sun has been open-sourced (GPL v2.0), in this case, a new virtual machine written in Java called Maxine. There are presentation slides available from JavaOne 2008. Maxine came out of nowhere as far as I’m concerned; I’m glad that Sun is still investing in this kind of research, and that they’re making it available as free software.
The Maxine project owners note a set of limitations, but I think the idea itself is interesting regardless of current limitations, although they note it’s not a new idea to write a JVM in Java itself. What may be new is that they are taking advantage of Java 5 features including generics, annotations, etc. which they believe gives them a leg up.
What I’m wondering is if this will, or could, ever be a useful replacement for HotSpot. I’d be surprised, but OTOH my sense in following the HotSpot mailing lists, as well as blog postings about it, is that HotSpot is a pretty damn complex piece of software. Certainly the advantages of writing in a higher-level language than C++ seem to make it worth the effort–or at least, an area worthy of investigation.
If you’re interested in these sorts of things, it’s worth keeping an eye on the Da Vinci Machine project, which aims to explore enhancements to the JVM to make it a better/more comfortable target for languages other than Java. I also recommend Cliff Click’s blog; Cliff used to work at Sun on the HotSpot server compiler. He is following interesting research on JVM implementation techniques and provides a useful map and commentary on what he finds.