Why to implement a JVM in Java?

(Reading notes for Chapter 10 of "Beautiful Architecture" - The Strength of Metacircular Virtual Machine: Jikes RVM)

I heard about Jikes RVM before as popular in the Java runtime environment research community, but I didn't think through what exactly implementing a JVM in Java benefits research in particular, or in general. I still held this question before I read this chapter.

This chapter is pretty clear. I especially like the part talking about myths surrounding runtime environments. It would be better if the book can also compare Jikes with other metacircular architectures, not necessary JVMs. Combining this chapter and some other articles, I think the advantages to implement a JVM in Java are two folds. First of all, it offers an opportunity to have better understanding of the language, especially how applications talk with run time environment and performance-critical features. So we can implement them in a better way. Secondly, in terms of performance, this implementation moves the Java/non-Java boundary crossing overhead below JVM instead of above JVM, which opens doors to more efficient implementation ideas and dynamic optimization opportunities. However, the question is that whether it is desirable to build a production-class JVM in Java. I still doubt it.

As a big system fan, I'm interested on how Jikes bootstraps itself and communicates with hardware/OS. I went through some research literals and found this paper, Implementing Jalapeño in Java, is a must-read. Jalapeño is the predecessor of Jikes. This paper describes the original motivation of the Jalapeño project in IBM Research and the challenges they encountered at the early age. Very interesting. You can find answers for these questions:

• How do they implement the first few essence components of a JVM, a not-very-efficient baseline compiler, a dynamic class loader, a simple memory manager and a debugger?
• How do they generate a boot-strap image of these components and load it to start Jalapeño?
• How does Jalapeño interface the hardware - through a special class MAGIC.
• How does Jalapeño interface the operating system - via ~1000 line C code to invoke system calls through the standard C library.

One thing that would have made this paper even more interesting is to talk more about the trade-offs between different implementation alternatives.